Earthquake motion analysis system

Abstract

To provide an earthquake motion analysis system for mesh dividing a stratum model in a proper element size in estimating an earthquake motion by finite element method analysis, to achieve a certain or higher analysis accuracy.SOLUTION: An earthquake motion analysis system 1 estimating an earthquake motion comprises: a stratum model creation part 2; a mesh division part 3 for mesh dividing the stratum model by each of a basic element size and a minute element size smaller than the basic element size, to create a basic mesh model and a minute mesh model; an earthquake motion analysis part 5 for estimating an earthquake motion by finite element method analysis to the mesh models, to derive a basic analysis result and a minute analysis result; and an accuracy determination part 6 for determining whether the accuracy of the basic analysis result is sufficient, and if it is determined that the accuracy is not sufficient, re-setting the basic element size to a smaller size. When the basic element size is reset, the mesh division part 3 creates the basic mesh model again, and the earthquake motion analysis part 5 derives the basic analysis result again.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a seismic motion analysis system for estimating seismic motion. [Background technology]

[0002] The finite element method is widely used to estimate earthquake motion. In finite element method analysis, a three-dimensional geological model is created based on the complex shape of the ground structure, this model is divided into meshes to create a mesh model as a collection of elements (meshes) with simple shapes that can be expressed mathematically, and earthquake motion is estimated by performing numerical analysis on each element in the mesh model.

[0003] In this regard, Patent Document 1 discloses a meshing program that divides a geological model to be meshed into a plurality of blocks and sequentially meshes each of these blocks from one end of the geological model to the other. In Patent Document 1, the size of the mesh elements is specified by input from outside. Patent Document 2 discloses a program that divides a geological model to be meshed into a plurality of blocks, meshes each block so that the nodes and connections at the boundary surface with an adjacent block match those of the adjacent block, and generates a mesh model corresponding to each block, thereby storing the mesh models corresponding to the geological model in a database as mesh models in block units. In this program, when a group of blocks to be combined is designated through a user interface, the program reads out the mesh models corresponding to the designated group of blocks from a storage device and combines them to generate a mesh model for a partial region of the geological model corresponding to the group of blocks to be combined. In Patent Document 2, the size of the mesh elements is specified by input from outside. Furthermore, Patent Document 3 discloses a geological wave propagation simulation system which, in a geological wave propagation simulation of a geological model, creates a geological model of the target of geological wave propagation, defines geological property values ​​in an area of ​​the geological model, creates an earthquake source model to be input, automatically creates a uniform mesh in the area where the geological property values ​​are defined, executes a geological wave propagation simulation by finite element method analysis according to the earthquake source model and analysis conditions, and displays the analysis results.

[0004] In the case of estimating earthquake motion by the finite element method as described above, if the size of the elements in the mesh division, i.e., the element size, is too large, the accuracy of the analysis results may be low. In this regard, in Patent Documents 1 and 2, the element size is input and specified from outside, and no judgment is made as to whether the input element size is appropriate or not. Therefore, even if a finite element method analysis is performed using the generated mesh model, the analysis accuracy may be low depending on the element size value used. Patent Document 3 also does not mention the setting of the element size, and therefore the analysis accuracy may be low depending on the element size value used. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5637956 [Patent Document 2] Patent No. 5762094 [Patent Document 3] JP 2002-122675 A Summary of the Invention [Problem to be solved by the invention]

[0006] The problem that the present invention aims to solve is to provide an earthquake motion analysis system that can achieve a certain level of analytical accuracy by dividing a geological model into meshes of appropriate element sizes when estimating earthquake motion using finite element analysis. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention employs the following means. That is, the earthquake motion analysis system of the present invention is an earthquake motion analysis system for estimating earthquake motion, and includes a geological layer model creation unit that creates a geological layer model based on the ground structure of an area to be analyzed, a mesh division unit that divides the geological layer model into meshes using a basic element size whose initial value is determined based on the period of the earthquake to be analyzed and a detailed element size that is smaller than the basic element size to create a basic mesh model and a detailed mesh model, a seismic source model creation unit that creates a seismic source model based on seismic source characteristics, and a basic analysis result that applies the seismic source model to each of the basic mesh model and the detailed mesh model to estimate the earthquake motion by finite element method analysis and and derives a detailed analysis result; and an accuracy determination unit that calculates a Fourier spectrum ratio of the basic analysis result to the detailed analysis result, determines whether or not the accuracy of the basic analysis result is sufficient based on the Fourier spectrum ratio, and resets the basic element size to a smaller value if it is determined that the accuracy is insufficient, and when the basic element size is reset, the mesh division unit mesh-divides the stratum model based on the reset basic element size to re-create the basic mesh model, and the earthquake motion analysis unit estimates the earthquake motion for the re-created basic mesh model, and re-derives the basic analysis result. According to the above-mentioned configuration, the geological model creation unit creates a geological model based on the ground structure of the area to be analyzed. This geological model is meshed by the mesh division unit with a basic element size whose initial value is determined based on the period of the earthquake to be analyzed, and a basic mesh model is generated. In the earthquake motion analysis unit, a seismic source model created by the seismic source model creation unit based on the seismic source characteristics is applied to the basic mesh model, earthquake motion is estimated by finite element method analysis, and a basic analysis result is derived. In this configuration, considering the processing time required for the analysis, it is desirable to make the basic element size as large as possible and reduce the number of elements that make up the basic mesh model, but on the other hand, if the basic element size is made too large, the analysis accuracy may be reduced. Here, when creating the basic mesh model, the mesh division unit simultaneously divides the stratum model into meshes using a detailed element size smaller than the basic element size to create a detailed mesh model, and the earthquake motion analysis unit also applies the earthquake source model to the detailed mesh model to estimate earthquake motion and derive a detailed analysis result. Since the detailed mesh model is divided into meshes using a detailed element size smaller than the basic element size, it has a smaller element size and a larger number of elements than the basic mesh model divided into meshes using the basic element size. Therefore, the detailed analysis result, which is the analysis result for this detailed mesh model, has a higher analysis accuracy than the basic analysis result. Therefore, if the basic analysis result is compared with the detailed analysis result having a higher analysis accuracy as described above, it is possible to efficiently determine whether the accuracy of the basic analysis result is insufficient. In the above configuration, the accuracy determination unit calculates the Fourier spectrum ratio of the basic analysis result to the detailed analysis result, and based on this, determines whether the accuracy of the basic analysis result is sufficient. Therefore, it is possible to efficiently determine whether the accuracy of the basic analysis result is sufficient. If the accuracy determination unit determines that the accuracy is insufficient, the basic element size is reset to a smaller value. The mesh division unit then divides the stratum model into meshes using the basic element size reset to a smaller value to create a basic mesh model again, and the earthquake motion analysis unit applies a seismic source model to the re-created basic mesh model to estimate earthquake motion and derive a basic analysis result again. Since the re-created basic mesh model is divided into meshes using the basic element size reset to a smaller value, it has a smaller element size and a larger number of elements than the previous basic mesh model before it is re-created. Therefore, the basic analysis result of this re-created basic mesh model has higher analysis accuracy than the basic analysis result of the previous basic mesh model that was previously analyzed and determined to have insufficient accuracy. Furthermore, while reducing the basic element size as described above, if it is determined that the accuracy of the basic analysis results is sufficient, the basic element size can be configured not to be reset to a smaller value, thereby preventing the basic element size from becoming excessively small and the basic mesh model from being divided into excessively fine meshes. In this way, the geological model is divided into meshes with more appropriate element sizes, and as a result, the analysis accuracy can be increased to a certain level or higher.

[0008] In one aspect of the present invention, the earthquake source model creation unit creates a plurality of the earthquake source models based on statistical values ​​of earthquake source characteristics, the earthquake motion analysis unit estimates the earthquake motion a plurality of times by sequentially applying each of the plurality of earthquake source models, the earthquake motion analysis unit estimates the earthquake motion for both the basic mesh model and the detailed mesh model and derives the basic analysis result and the detailed analysis result only when the first earthquake source model among the plurality of earthquake source models is applied to estimate the earthquake motion for the first time, and in other cases, estimates the earthquake motion only for the latest basic mesh model and derives the basic analysis result, and the accuracy determination unit determines the accuracy of the basic analysis result and resets the basic element size only when the first earthquake source model is applied to estimate the earthquake motion. In general, source characteristics are created by performing inversion based on observation records of past earthquakes to estimate source characteristics equivalent to these. If statistical values ​​such as average values ​​and variations (standard deviations) are known or estimated for each characteristic, multiple values ​​can be set for each characteristic according to the range of variation. Therefore, multiple source models can be created based on the statistical values ​​of source characteristics. According to the above configuration, the earthquake source model creation unit creates multiple earthquake source models based on the statistics of the earthquake source characteristics, and the earthquake motion analysis unit estimates earthquake motion multiple times by sequentially applying each of the multiple earthquake source models. This makes it possible to estimate earthquake motion taking into account the statistics of the earthquake source characteristics. Here, the earthquake motion analysis unit estimates earthquake motion multiple times by sequentially applying each of the multiple earthquake source models, so if earthquake motion for both the basic mesh model and the detailed mesh model were to be estimated for each of the multiple earthquake source models as described above, a significant amount of analysis time would be required. However, in estimating earthquake motion using a detailed mesh model, the purpose is to compare the detailed analysis results with the basic analysis results of the basic mesh model to determine whether the accuracy of the basic analysis results is sufficient, and to adjust the basic element size to be smaller when meshing the basic mesh model as necessary. Therefore, once the basic element size is set appropriately small enough to determine that the accuracy of the basic analysis results is sufficient in an analysis applying the first of multiple earthquake source models, and the basic mesh model is appropriately meshed, in subsequent analyses applying the second and subsequent earthquake source models, if the same basic mesh model meshed with the same basic element size is used to estimate earthquake motion, it can be generally guaranteed that the accuracy of the basic analysis results will be sufficient in the subsequent analyses. Furthermore, when it is determined in an analysis applying the first of multiple seismic source models that the accuracy of the basic analysis results is insufficient, the basic mesh model is re-created to estimate seismic motion, the basic analysis results are re-derived and compared with the detailed analysis results, and this process is repeated until it is determined that the accuracy of the basic analysis results is sufficient. Even if this is repeated, the detailed analysis results should basically have high analytical accuracy when they are created for the first time, so there is little need to re-create the detailed mesh model and estimate seismic motion. Based on this idea, in the above configuration, the earthquake motion analysis unit estimates earthquake motion for both the basic mesh model and the detailed mesh model only when the first earthquake motion is estimated by applying the first earthquake motion model among the multiple earthquake motion models, and derives the basic analysis result and the detailed analysis result. In other words, when the earthquake motion analysis unit estimates earthquake motion for the second or subsequent times by applying the first earthquake motion model, the earthquake motion analysis unit does not estimate earthquake motion for the detailed mesh model. Also, even when estimating earthquake motion by applying an earthquake motion model other than the first earthquake motion model, the earthquake motion analysis unit does not estimate earthquake motion for the detailed mesh model, but estimates earthquake motion only for the latest basic mesh model that was generated last and was determined to have sufficient accuracy of the basic analysis result as a result of estimating earthquake motion by applying the first earthquake motion model, and derives the basic analysis result. In this way, it is possible to reduce the number of times earthquake motion is estimated for the detailed mesh model, thereby reducing the analysis time, while maintaining a certain level of analysis accuracy when all earthquake motion models are applied.

[0009] In another aspect of the present invention, the initial value of the basic element size is a value obtained by dividing the wavelength of the earthquake to be analyzed by a value greater than or equal to 5 and less than 10, and the detailed element size is half of that value. It is generally known that mesh division using a value obtained by dividing the wavelength of an earthquake by 5 as the element size improves the accuracy of analysis. According to the above-mentioned configuration, the upper limit of the initial value of the basic element size before being reset in the subsequent processing is the value obtained by dividing the wavelength of the earthquake to be analyzed by 5, so that the accuracy judgment unit is more likely to judge that the accuracy is sufficient in the initial judgment of whether the accuracy of the basic analysis result is sufficient. Therefore, the number of times that a series of processes is executed, which includes resetting the basic element size to a smaller value, mesh-dividing the stratum model with this reset basic element size, recreating the basic mesh model, estimating the earthquake motion for the re-created basic mesh model, and re-deriving the basic analysis result, is reduced. Furthermore, by setting the detailed element size to half the initial value of the basic element size, the detailed element size can be made sufficiently small to ensure sufficiently high accuracy of the detailed analysis results for the detailed mesh model, which are used as a comparison target to ensure the accuracy of the basic analysis results for the basic mesh model. Here, the basic element size for dividing the basic mesh model into meshes should be larger than the detailed element size for dividing the detailed mesh model into meshes. In the above case, since the upper limit of the initial value of the basic element size is the value obtained by dividing the wavelength of the earthquake by 5, the detailed element size at its maximum will be 1 / 2 of that value, i.e., the value obtained by dividing the wavelength of the earthquake by 10. In other words, by setting the lower limit of the initial value of the basic element size to the value obtained when the detailed element size is at its maximum, the initial value of the basic element size will be smaller than the value that can be adopted as the detailed element size, and the basic mesh model will be prevented from being divided into excessively small meshes.

[0010] The earthquake motion analysis system of the present invention is an earthquake motion analysis system for estimating earthquake motion, and includes a geological layer model creation unit that creates a geological layer model based on the ground structure of an area to be analyzed, a mesh division unit that divides the geological layer model into meshes using a basic element size whose initial value is determined based on the period of the earthquake to be analyzed and a detailed element size that is smaller than the basic element size to create a basic mesh model and a detailed mesh model, a seismic source model creation unit that creates a seismic source model based on seismic source characteristics, a seismic source model that applies the seismic source model to each of the basic mesh model and the detailed mesh model to estimate the earthquake motion by finite element method analysis, and derives a basic analysis result and a detailed analysis result, and and an accuracy determination unit that calculates a Fourier spectral ratio, determines whether or not the accuracy of the basic analysis result is sufficient based on the Fourier spectral ratio, and resets the basic element size to a smaller value if it is determined that the accuracy is insufficient, and when the basic element size is reset, the accuracy determination unit resets the basic element size to the value of the detailed element size, changes the detailed mesh model to the basic mesh model, and resets the detailed element size to a smaller value, the mesh division unit mesh-divides the stratum model based on the reset detailed element size to re-create the detailed mesh model, and the earthquake motion analysis unit estimates the earthquake motion for the re-created detailed mesh model, and re-derives the detailed analysis result. According to the above-mentioned configuration, the geological model creation unit creates a geological model based on the ground structure of the area to be analyzed. This geological model is meshed by the mesh division unit with a basic element size whose initial value is determined based on the period of the earthquake to be analyzed, and a basic mesh model is generated. In the earthquake motion analysis unit, a seismic source model created by the seismic source model creation unit based on the seismic source characteristics is applied to the basic mesh model, earthquake motion is estimated by finite element method analysis, and a basic analysis result is derived. In this configuration, considering the processing time required for the analysis, it is desirable to make the basic element size as large as possible and reduce the number of elements that make up the basic mesh model, but on the other hand, if the basic element size is made too large, the analysis accuracy may be reduced. Here, when creating the basic mesh model, the mesh division unit simultaneously divides the stratum model into meshes using a detailed element size smaller than the basic element size to create a detailed mesh model, and the earthquake motion analysis unit also applies the earthquake source model to the detailed mesh model to estimate earthquake motion and derive a detailed analysis result. Since the detailed mesh model is divided into meshes using a detailed element size smaller than the basic element size, it has a smaller element size and a larger number of elements than the basic mesh model divided into meshes using the basic element size. Therefore, the detailed analysis result, which is the analysis result for this detailed mesh model, has a higher analysis accuracy than the basic analysis result. Therefore, if the basic analysis result is compared with the detailed analysis result having a higher analysis accuracy as described above, it is possible to efficiently determine whether the accuracy of the basic analysis result is insufficient. In the above configuration, the accuracy determination unit calculates the Fourier spectrum ratio of the basic analysis result to the detailed analysis result, and based on this, determines whether the accuracy of the basic analysis result is sufficient. Therefore, it is possible to efficiently determine whether the accuracy of the basic analysis result is sufficient. If the accuracy determination unit determines that the accuracy is insufficient, the basic element size is reset to a smaller value, such as the value of the detailed element size at the current stage. Then, the detailed mesh model is changed to the basic mesh model. Since this basic mesh model is the same as the detailed mesh model, the basic analysis result can be the same as the detailed analysis result at this point in time. The accuracy determination unit resets the detailed element size to a smaller value, the mesh division unit mesh-divides the stratum model with the reset detailed element size to create a detailed mesh model again, and the earthquake motion analysis unit estimates earthquake motion for the detailed mesh model created again to derive the detailed analysis result again. In this way, both the basic mesh model and the detailed mesh model are mesh-divided finer than the basic mesh model and the detailed mesh model at the time when the accuracy determination unit determined that the accuracy was insufficient. Therefore, the accuracy of the basic analysis result and the detailed analysis result corresponding to each of them is improved, and the possibility of determining that the accuracy of the basic analysis result is sufficient is increased. Furthermore, while reducing the basic element size as described above, if it is determined that the accuracy of the basic analysis results is sufficient, the basic element size can be configured not to be reset to a smaller value, thereby preventing the basic element size from becoming excessively small and the basic mesh model from being divided into excessively fine meshes. In this way, the geological model is divided into meshes with an appropriate element size, and as a result, the analysis accuracy can be increased to a certain level or higher. Effect of the Invention

[0011] According to the present invention, it is possible to provide an earthquake motion analysis system that can achieve a certain level of analytical accuracy by dividing a geological model into meshes of appropriate element sizes when estimating earthquake motion using finite element analysis. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a block diagram of a seismic motion analysis system. [Diagram 2] FIG. 1 is an explanatory diagram of an analysis area in which public data exists. [Diagram 3] FIG. 13 is an explanatory diagram regarding extrapolation of a range where no public data exists. [Figure 4] FIG. 1 is an explanatory diagram of a seismic source model. [Diagram 5] FIG. 13 is an explanatory diagram of a Fourier spectrum ratio of a basic analysis result to a detailed analysis result. [Figure 6] 4 is a flowchart of a seismic motion analysis method using the above-mentioned seismic motion analysis system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention is a seismic motion analysis system that estimates ground shaking during an earthquake by finite element analysis. In the seismic motion analysis system, the ground structure close to the ground surface is meshed into two types of layer models using a basic element size determined based on the earthquake period and a detailed element size smaller than the basic element size, and the validity of the calculation accuracy is verified for the analytical value in the periodic band to be analyzed, thereby obtaining highly reliable seismic motion. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. [First embodiment] FIG. 1 is a block diagram of a seismic motion analysis system according to this embodiment. The earthquake motion analysis system 1 in this embodiment estimates earthquake motion by the finite element method. The earthquake motion analysis system 1 creates a mesh model for an area including a target point for which earthquake motion is to be estimated, for example, where a building is planned to be constructed or a building has already been constructed, and analyzes and estimates earthquake motion for the mesh model by the finite element method. The earthquake motion analysis system 1 includes a layer model creation unit 2, a mesh division unit 3, a source model creation unit 4, an earthquake motion analysis unit 5, an accuracy determination unit 6, and a post-processing unit .

[0014] The geological layer model creation unit 2 creates a geological layer model based on the ground structure of an analysis area, which is an area to be analyzed. FIG. 2 is an explanatory diagram of the analysis domain within which public data exists. The geological layer model creation unit 2 creates a geological layer model for an analysis area R that is input and set in advance. The analysis area R may be set as, for example, a rectangular parallelepiped shape. When viewed in a plan view as in FIG. 2, the analysis area R may be set as a certain area surrounded by a rectangular shape on the map. In this case, the analysis area R may be set by the latitude and longitude of the lower left vertex O of the rectangular shape, the lengths E1 and E2 of the two mutually perpendicular sides of the rectangular shape, and the rotation angle θ. The analysis area R is set so as to have a certain area in the depth direction in FIG. 2, i.e., in the depth direction on the map. That is, the analysis area R is set using the depth from the earth's surface in addition to the above parameters.

[0015] The stratum model creation unit 2 divides the analysis domain R set as described above into grids in two directions perpendicular to each other on a horizontal plane. Next, the stratum model creation unit 2 divides each of the divided grids on the stratum surface. More specifically, at each intersection of the grids obtained by dividing the analysis region R in the horizontal plane, layer boundary data of the ground structure at the location of the intersection is obtained, and based on this layer boundary data, a plane including the same stratum at each grid intersection is formed as a stratum surface, thereby dividing each grid in the depth direction. Layer boundary data indicates the depth from the ground surface to each layer surface. For layer boundary data, public data such as the deep ground structure of the J-SHIS earthquake hazard station, the first nationwide underground structure model of the Headquarters for Earthquake Research Promotion, and the integrated shallow and deep ground structure model can be used. When using the above-mentioned public data, there are cases where data cannot be obtained at the intersection of the grid divided by the geological model creation unit 2. In such a case, it is sufficient to obtain multiple public data in the vicinity of the intersection, and based on this, to obtain the position of the geological surface at the intersection by spatially interpolating.

[0016] FIG. 3 is an explanatory diagram regarding extrapolation of a range where no public data exists. When it is desired to include an area not included in the public data as described above in the analysis area R, the range R1 of the public data may be extended to set the analysis area R, as shown in Fig. 3. Specifically, for example, in a case where the epicenter region RE, which is the area where the epicenter is located, is not included in the range R1 of the public data, the range R1 of the public data may be extended in the direction in which the contour line L extends to create an extrapolation area R2, thereby adding the extrapolation area R2 to the range R1 of the public data to create the analysis area R. In this case, data at each point in the extrapolation area R2 may be generated by copying data at the boundary part of the range R1 of the public data with the extrapolation area R2 to the extrapolation area R2. In this manner, the geological layer model creation unit 2 creates a geological layer model, which is data on the depth from the ground surface to each layer surface within the analysis region R.

[0017] Next, the mesh division unit 3 divides the stratum model created by the stratum model creation unit 2 into meshes to create a mesh model. The mesh division unit 3 first divides the geological layer model into meshes to create a basic mesh model. The basic mesh model is a mesh model that is mainly used for the analysis and estimation of earthquake motion in the subsequent processes. The earthquake motion analysis system 1 receives an input of an analysis period. The analysis period can be determined based on the natural period of a building that is to be constructed or has already been constructed at a target location where earthquake motion is to be estimated, so as to include the period of an earthquake to be analyzed that may affect the building. In addition, the velocity of S-waves on the ground surface, Vs, can be roughly determined depending on the ground conditions at the target point where seismic motion is to be estimated. The wavelength of the earthquake to be analyzed is determined based on the analysis period and the S-wave velocity. It is generally known that analysis accuracy is improved by dividing the mesh into elements with the element size calculated by dividing the wavelength of an earthquake by 5. Therefore, the initial value of the basic element size, which is the element size used when dividing the basic mesh model into meshes, is determined by dividing the wavelength of an earthquake determined as described above by, for example, 5. More specifically, it is desirable to determine the initial value of the basic element size as a value obtained by dividing the wavelength of the earthquake to be analyzed by a value equal to or greater than 5 and less than 10.

[0018] The mesh division unit 3 divides each grid into cubes with the basic element size determined as above as the length of one side for each division by the strata surface. The mesh division unit 3 further divides each cube into a plurality of tetrahedrons. Since the strata surface may be inclined, for example, the mesh division unit 3 may divide the grid into tetrahedrons near the strata surface without first dividing the grid into cubes. In this way, the mesh division unit 3 divides the stratum model into meshes based on the basic element size whose initial value is determined based on the period of the earthquake to be analyzed, to create a basic mesh model. Each of the meshes constituting the basic mesh model is assigned an identification number.

[0019] Next, the mesh division unit 3 divides the stratum model into meshes to create a detailed mesh model. The detailed mesh model is used as a comparison target in the subsequent processing when determining whether the accuracy of the result of estimating seismic motion is sufficient for the basic mesh model. The detailed element size, which is the element size when dividing the detailed mesh model into meshes, is determined to be smaller than the basic element size. In this embodiment, the detailed element size is half the initial value of the basic element size. The mesh division unit 3 divides the stratum model into meshes according to the detailed element size in the same manner as in the basic mesh model, to create a detailed mesh model. Each of the meshes constituting the detailed mesh model is assigned an identification number.

[0020] The earthquake source model creation unit 4 creates an earthquake source model based on the earthquake source characteristics. Figure 4 is an explanatory diagram of the earthquake source model. As shown in Figure 4, the seismic region RE is a certain, widespread area when viewed in a plan view. Point seismic sources P are placed at appropriate intervals within this seismic region RE. Point seismic sources P are also placed within the asperity region RA, which is a region of asperities located within the seismic region RE.

[0021] Each of the point seismic sources P is located inside a rectangular parallelepiped that forms the outer periphery of the geological layer model. Therefore, each of the point seismic sources P is located inside one of the meshes that constitute the basic mesh model in which the geological layer model is divided according to the basic element size. For each of the point seismic sources P, the seismic source model creation unit 4 obtains the identification number of the mesh of the basic mesh model in which the point seismic source P is located and corresponds to the point seismic source P. Similarly, each point seismic source P is located inside one of the meshes constituting the detailed mesh model in which the stratum model is divided by the detailed element size. For each point seismic source P, the seismic source model creation unit 4 obtains the identification number of the mesh of the detailed mesh model in which the point seismic source P is located and corresponds to the point seismic source P.

[0022] The source properties include the strike angle, dip angle, slip angle, seismic moment, and slip velocity time function of the fault. The values ​​of these source properties are set individually for each point source P. In general, source characteristics are created by performing inversion so as to estimate source characteristics equivalent to past earthquake observation records. Here, if statistical values ​​such as the average value and variation (standard deviation) for each characteristic are known or estimated, multiple values ​​can be set for each characteristic according to the range of variation. Therefore, multiple values ​​can be set for each point source P based on the statistical values ​​of the source characteristics. For this reason, the source model creation unit 4 creates multiple different source models in which different values ​​of the source characteristics are set for the point source P. In these multiple source models, the position of the point source P is common, but the values ​​of the source characteristics set for the point source P are different. The number of earthquake source models may be around 1,000 if one tries to create earthquake source models within the 3σ range of normal distribution, for example. In this manner, the earthquake source model creation unit creates a plurality of earthquake source models based on the statistical values ​​of earthquake source characteristics.

[0023] The earthquake motion analysis unit 5 applies the earthquake source model to the basic mesh model, analyzes and estimates earthquake motion by finite element method analysis, and derives basic analysis results. First, the earthquake motion analysis unit 5 acquires a first earthquake source model from among a plurality of earthquake source models. Next, the seismic motion analysis unit 5 obtains, for each point seismic source P in the first seismic source model, the identification number of the mesh of the basic mesh model corresponding to that point seismic source P, and sets the value of the seismic source characteristics set for that point seismic source P in the first seismic source model to each of the nodes that constitute the mesh of that identification number. For the basic mesh model to which the first seismic source model is applied in this way, the earthquake motion analysis unit 5 estimates earthquake motion by finite element analysis and derives a basic analysis result. The basic analysis result may include an acceleration time history waveform, a velocity time history waveform, and a displacement time history waveform in three directions, namely, north-south, east-west, and up-down (depth), at each node of the basic mesh model. The analysis of the basic mesh model using the second and subsequent seismic source models will be explained later.

[0024] The earthquake motion analysis unit 5 applies the earthquake source model to the detailed mesh model, analyzes and estimates earthquake motion by finite element method analysis, and derives detailed analysis results. The seismic motion analysis unit 5 first obtains, for each point seismic source P in the first seismic source model obtained by analyzing the basic mesh model, an identification number of the mesh in the detailed mesh model that corresponds to the point seismic source P, and sets the value of the seismic source characteristics that were set for the point seismic source P in the first seismic source model to each of the nodes that constitute the mesh of the identification number. For the detailed mesh model to which the first seismic source model has been applied in this way, the earthquake motion analysis unit 5 estimates earthquake motion by finite element analysis and derives detailed analysis results. The detailed analysis results may include, like the basic analysis results, acceleration time history waveforms, velocity time history waveforms, and displacement time history waveforms in three directions, north-south, east-west, and up-down (depth), at each node of the basic mesh model. In this way, the earthquake motion analysis unit 5 applies the first earthquake source model among multiple earthquake source models to each of the basic mesh model and the detailed mesh model, estimates earthquake motion using finite element method analysis, and derives basic analysis results and detailed analysis results.

[0025] FIG. 5 is an explanatory diagram of the Fourier spectrum ratio of the basic analysis result to the detailed analysis result. Since the detailed mesh model is divided into meshes with a detailed element size smaller than the basic element size, the element size is smaller and the number of elements is larger than that of the basic mesh model divided into meshes with the basic element size. Therefore, the detailed analysis result, which is the analysis result for this detailed mesh model, has higher analysis accuracy than the basic analysis result. Therefore, by comparing the basic analysis result with the detailed analysis result having higher analysis accuracy, it is possible to efficiently determine if the accuracy of the basic analysis result is insufficient. Based on this idea, the accuracy determination unit 6 determines whether the accuracy of the basic analysis result is sufficient or not based on the calculated Fourier spectrum ratio. Specifically, the accuracy determination unit 6 uses the Fourier spectrum ratio to compare how close the basic analysis result is to the detailed analysis result, and determines that the calculation accuracy of the basic analysis result is sufficient if the Fourier spectrum ratio is between the lower threshold and the upper threshold. In this way, the reliability of the analysis accuracy is confirmed.

[0026] 5 shows a case where the analysis cycle F is, for example, 3 or more. In this embodiment, for example, in a cycle equal to or more than this analysis cycle F, it is calculated whether or not the Fourier spectrum ratio is between a lower threshold and an upper threshold, and if it is equal to or more than the lower threshold LB and equal to or less than the upper threshold UB, it is determined that the accuracy of the basic analysis result is sufficient. In general, if the Fourier spectrum ratio of two earthquake motions is within a range of 1 / 2, they tend to be considered to be almost equal. Therefore, in this embodiment, the lower threshold LB and upper threshold UB are set to 0.5 and 2, respectively, and if the Fourier spectrum ratio is within a range of 1 / 2, the accuracy of the basic analysis result is determined to be sufficient. In a case where a more strict determination is required, the lower threshold LB and the upper threshold UB may be set to, for example, 0.8 and 1.2, respectively.

[0027] In FIG. 5, in analysis cycles F of 3 or more, the Fourier spectrum ratio is equal to or greater than the lower threshold LB and equal to or less than the upper threshold UB, so that the accuracy determining unit 6 determines that the accuracy of the basic analysis result is sufficient. In this case, the basic mesh model is considered to be appropriately divided into meshes with an appropriately sized basic element to obtain analysis results with sufficient accuracy. Therefore, even if an analysis is performed on a basic mesh model that has already been analyzed using the first seismic source model by applying a seismic source model other than the first seismic source model among multiple seismic source models, the accuracy of the resulting basic analysis results is considered to be sufficient. Based on this idea, in this embodiment, when other earthquake source models after the second earthquake source model are applied to analyze and estimate seismic motion, the accuracy assessment unit 6 does not calculate the Fourier spectral ratio or assess the accuracy.

[0028] More specifically, the earthquake motion analysis unit 5 first acquires the next earthquake source model, i.e., the second earthquake source model, from among the multiple earthquake source models. As in the case of the first earthquake source model, the earthquake motion analysis unit 5 uses the same basic mesh model as that already analyzed by applying the first earthquake source model, and sets the values ​​of the earthquake source characteristics set for the point earthquake source P in the second earthquake source model to each of the nodes constituting the mesh of the basic mesh model. After that, the earthquake motion analysis unit 5 estimates earthquake motion by finite element analysis for the basic mesh model to which the second earthquake source model is applied, and derives the basic analysis result. In this way, the earthquake motion analysis unit 5 applies each of the earthquake source models to the basic mesh model to derive a basic analysis result for each of the earthquake source models. The earthquake motion analysis unit 5 estimates earthquake motion multiple times by sequentially applying each of the earthquake source models. As described above, when estimating seismic motion by applying other seismic source models after the second seismic source model, seismic motion is not estimated for the detailed mesh model, but is estimated only for the basic mesh model to derive basic analysis results.

[0029] In the above judgment by the accuracy judgment unit 6, if the Fourier spectral ratio, for example, partially or entirely, is below the lower threshold LB or is above the upper threshold UB, the accuracy judgment unit 6 judges that the accuracy of the basic analysis result is insufficient. The reason why the accuracy of the basic analysis result is insufficient is believed to be that the basic element size, which is the element size when dividing the geological layer model into the basic mesh model, is not small enough, and the basic mesh model is not divided into meshes of a sufficiently small size. Therefore, when it is determined that the accuracy of the basic analysis result is insufficient, the accuracy determination unit 6 resets the basic element size to a value smaller than the value currently set as the basic element size. Basically, in this embodiment, the detailed mesh model is divided into meshes with a sufficiently fine detailed element size so that the accuracy of the detailed analysis results is sufficiently high. In addition, considering that all earthquake source models are applied to the basic mesh model to repeatedly estimate earthquake motion, it is desirable to set the basic element size for dividing the basic mesh model into meshes as large as possible to reduce the time required for analysis. From this perspective, it is desirable to set the value for resetting the basic element size to a value larger than the detailed element size. For example, it is conceivable to multiply the basic element size by a value between 0.7 and 0.9 and reset the value as a new basic element size.

[0030] Next, the mesh division unit 3 divides the geological layer model created by the geological layer model creation unit 2 into meshes using the basic element size reset to a smaller value by the accuracy determination unit 6, and recreates the basic mesh model. In this case, in this embodiment, the mesh division unit 3 does not create a detailed mesh model again. Furthermore, the earthquake source model creation unit 4 does not create the earthquake source model again. However, by creating the basic mesh model again with the basic element size reset to a smaller value, the correspondence between the point earthquake source P and the mesh in the basic mesh model also changes. For this reason, the earthquake source model creation unit 4 obtains, for each point earthquake source P, the identification number of the mesh of the basic mesh model in which the point earthquake source P is located and corresponds to the point earthquake source P, and associates it with the point earthquake source P again.

[0031] Then, the earthquake motion analysis unit 5 estimates earthquake motion for the re-created basic mesh model and derives the basic analysis result again. More specifically, the earthquake motion analysis unit 5 applies the first earthquake source model to the re-created basic mesh model by setting the values ​​of the earthquake source characteristics of each point earthquake source P of the first earthquake source model used in the analysis when it was determined that the accuracy of the basic analysis result was insufficient to the nodes of the mesh corresponding to the point earthquake source P of the re-created basic mesh model, and derives the basic analysis result again. In this embodiment, the basic mesh model is re-created and updated, but the detailed mesh model is not created, and the one created initially is maintained. Therefore, when estimating earthquake motions for the second or subsequent times by applying the first earthquake source model, the earthquake motion analysis unit 5 does not estimate earthquake motions for the detailed mesh model.

[0032] When the estimation of earthquake motion for the re-created basic mesh model is completed, the accuracy evaluation unit 6 compares the basic analysis result, which is the result of the initial estimation of earthquake motion by applying the first earthquake source model among the multiple earthquake source models, with the detailed analysis result previously derived together with the basic analysis result. Specifically, the accuracy evaluation unit 6 compares the new basic analysis result with the detailed analysis result by calculating the Fourier spectrum ratio of the acceleration time history waveform newly output as the basic analysis result to the acceleration time history waveform previously output as the detailed analysis result. The accuracy determination unit 6 determines whether the accuracy of the new basic analysis result is sufficient based on the calculated Fourier spectrum ratio. If the accuracy determination unit 6 determines that the accuracy of the basic analysis result is not sufficient, the basic element size is reset to a smaller value and the mesh division unit 3 creates a basic mesh model again. Furthermore, the seismic source model creation unit 4 applies the first seismic source model to the recreated basic mesh model by setting the values ​​of the seismic source characteristics set for the point seismic source P to the nodes of the recreated basic mesh model, thereby deriving the basic analysis result again.

[0033] The above-mentioned reconfiguration of the basic element size, creation of the basic mesh model, and analysis of the basic mesh model using the first seismic source model are repeatedly performed until the accuracy assessment unit 6 determines that the accuracy of the basic analysis results is sufficient. As a result of this repetition, the final basic mesh model is divided into meshes fine enough to obtain sufficient analytical accuracy. In this way, when the accuracy assessment unit 6 determines that the accuracy of the basic analysis results is sufficient, the seismic motion analysis unit 5 uses the last created basic mesh model to set the values ​​of the seismic source characteristics set for the point source P of all seismic source models other than the first seismic source model among the multiple seismic source models to the nodes of the last created basic mesh model, and then performs an estimation of seismic motion for the last created basic mesh model to derive the basic analysis results.

[0034] In this way, the earthquake motion analysis unit 5 estimates earthquake motion for both the basic mesh model and the detailed mesh model and derives basic analysis results and detailed analysis results only when the first earthquake motion is estimated by applying the first earthquake motion model among multiple earthquake motion models for the first time. In addition, in other cases, i.e., when the first seismic source model is applied to estimate seismic motion for the second or subsequent times, or when another seismic source model other than the first seismic source model is applied to estimate seismic motion, the seismic motion analysis unit 5 estimates seismic motion only for the latest basic mesh model that was last generated, and derives the basic analysis results. In the case where the accuracy determination unit 6 determines in the initial determination that the accuracy of the basic analysis result of the basic mesh model is sufficient and, as a result, the basic mesh model is created only once the initial time, the latest basic mesh model is the basic mesh model created in the initial time. In the case where the accuracy determination unit 6 determines that the accuracy of the basic analysis result of the basic mesh model is not sufficient and, as a result, the basic mesh model is created multiple times, the latest basic mesh model is the one created last among the multiple basic mesh models created. Moreover, the accuracy determining unit 6 determines the accuracy of the basic analysis results and resets the basic element size only when the first earthquake source model is applied to estimate earthquake motion.

[0035] The post-processing unit 7 performs post-processing on the multiple basic analysis results generated by applying each of the multiple earthquake source models to the basic mesh model and performing analysis as described above. The post-processing includes waveform processing such as calculation of Fourier spectrum and response spectrum for the basic analysis results, and calculation of statistics such as average value per period and natural logarithm standard deviation.

[0036] Next, a method of earthquake motion analysis using the earthquake motion analysis system 1 will be described with reference to Figures 1 to 5 and 6. Figure 6 is a flowchart of the earthquake motion analysis method. First, the geological layer model creating unit 2 creates a geological layer model, which is data on the depth from the ground surface to each layer surface within the analysis region R (step S1). Next, the mesh division unit 3 divides the geological layer model into meshes according to the basic element size to create a basic mesh model. The mesh division unit 3 also divides the geological layer model into meshes according to the detailed element size to create a detailed mesh model (step S2). The earthquake source model creation unit 4 creates an earthquake source model based on the earthquake source characteristics (step S3). For each point earthquake source P, the earthquake source model creation unit 4 obtains an identification number of a mesh of the basic mesh model where the point earthquake source P is located and corresponds to the point earthquake source P. In addition, for each point earthquake source P, the earthquake source model creation unit 4 obtains an identification number of a mesh of the detailed mesh model where the point earthquake source P is located and corresponds to the point earthquake source P. The earthquake motion analysis unit 5 then applies a first earthquake source model among the multiple earthquake source models to the basic mesh model, estimates earthquake motion by finite element method analysis, and derives a basic analysis result.Furthermore, the earthquake motion analysis unit 5 applies a first earthquake source model to the detailed mesh model, estimates earthquake motion by finite element method analysis, and derives a detailed analysis result (step S4).

[0037] Thereafter, the accuracy determining unit 6 determines whether or not the analysis performed by the earthquake motion analyzing unit 5 was performed by applying the first earthquake source model among the multiple earthquake source models (step S5). If the analysis was performed using the first seismic source model (Yes in step S5), the accuracy assessment unit 6 calculates the Fourier spectral ratio of the acceleration time history waveform output as the basic analysis result to the acceleration time history waveform output as the detailed analysis result when the first seismic source model was applied (step S6). Then, the accuracy determining unit 6 determines whether or not the accuracy of the basic analysis result is sufficient based on the calculated Fourier spectrum ratio (step S7).

[0038] If it is determined that the accuracy of the basic analysis result is not sufficient (No in step S7), the accuracy determination unit 6 resets the basic element size to a value smaller than the value currently set as the basic element size (step S9). Then, the process proceeds to step S2, where the mesh division unit 3 divides the geological layer model created by the geological layer model creation unit 2 into meshes using the basic element size that has been reset to a smaller value by the accuracy determination unit 6, to recreate a basic mesh model. In this case, in this embodiment, the mesh division unit 3 does not create a detailed mesh model again. In addition, the earthquake source model creation unit 4 does not create the earthquake source model again. However, for each point earthquake source P, the earthquake source model creation unit 4 obtains the identification number of the mesh of the basic mesh model in which the point earthquake source P is located and corresponds to the point earthquake source P, and associates it with the point earthquake source P again (step S3). Then, the earthquake motion analysis unit 5 applies a first earthquake source model among the multiple earthquake source models to the re-created basic mesh model, estimates earthquake motion by finite element method analysis, and derives basic analysis results (step S4). In this embodiment, the basic mesh model is re-created and updated, but the detailed mesh model is not created, and the one created initially is maintained. Therefore, when estimating earthquake motions for the second or subsequent times by applying the first earthquake source model, the earthquake motion analysis unit 5 does not estimate earthquake motions for the detailed mesh model.

[0039] Thereafter, the accuracy determination unit 6 determines whether the analysis performed by the earthquake motion analysis unit 5 is performed by applying the first earthquake source model among the multiple earthquake source models (step S5). In this case, since the analysis is performed for the second time by applying the first earthquake source model, the process proceeds to step S6. The accuracy determination unit 6 calculates the Fourier spectrum ratio of the acceleration time history waveform output again as the basic analysis result to the acceleration time history waveform output as the detailed analysis result when the first earthquake source model is applied (step S6). Then, the accuracy determining unit 6 determines whether or not the accuracy of the re-derived basic analysis result is sufficient based on the calculated Fourier spectrum ratio (step S7). In this manner, the series of processes from step S9 to step S6, including setting the basic element size to a small value, creating a basic mesh model using the small basic element size, estimating seismic motion for the basic mesh model using the first seismic source model, and calculating the Fourier spectral ratio, are repeated until it is determined in step S7 that the accuracy is sufficient.

[0040] If it is determined that the accuracy of the basic analysis result is sufficient (Yes in step S7), the earthquake motion analysis unit 5 acquires the next earthquake source model, for example the second earthquake source model, from among the multiple earthquake source models (step S8). Then, the process proceeds to step S4, where the seismic motion is analyzed and estimated by finite element analysis for the finally created basic mesh model to which the second seismic source model has been applied, and basic analysis results are derived. When estimating earthquake motion by applying other earthquake source models after the second earthquake source model, the earthquake motion analysis unit 5 does not estimate earthquake motion for the detailed mesh model. In the next step S5, since the analysis does not apply the first earthquake source model in this case, the process proceeds to step S10. Therefore, the calculation of the Fourier spectrum ratio in step S6 and the accuracy determination process in step S7 are not performed.

[0041] In step S10, it is determined whether or not analysis has been performed by applying all the earthquake source models to the basic mesh model. If the analysis using all earthquake source models has not been completed and there are earthquake source models that have not been applied (No in step S10), the next earthquake source model, for example the third earthquake source model, is selected from the multiple earthquake source models (step S8). Then, the process proceeds to step S4, where seismic motion is estimated by finite element analysis for the basic mesh model to which the third seismic source model has been applied, and basic analysis results are derived. In this manner, the selection of a new earthquake source model and the analysis using that new earthquake source model in steps S4 and S8 are repeated until it is determined in step S10 that analysis has been performed using all earthquake source models. If it is determined that the analysis applying all the earthquake source models has been completed (Yes in step S10), the post-processing unit 7 performs post-processing on the multiple basic analysis results generated by applying each of the multiple earthquake source models to the last created basic mesh model and analyzing them as described above (step S11), and then terminates the processing.

[0042] Next, the effects of the above earthquake motion analysis system will be described. The earthquake motion analysis system 1 as described above is an earthquake motion analysis system 1 that estimates earthquake motion, and includes a geological layer model creation unit 2 that creates a geological layer model based on the ground structure of the area to be analyzed, a mesh division unit 3 that divides the geological layer model into meshes using a basic element size whose initial value is determined based on the period of the earthquake to be analyzed and a detailed element size that is smaller than the basic element size to create a basic mesh model and a detailed mesh model, a seismic source model creation unit 4 that creates a seismic source model based on seismic source characteristics, and a seismic source model that applies the seismic source model to each of the basic mesh model and the detailed mesh model to estimate earthquake motion by finite element method analysis. The system is equipped with an earthquake motion analysis unit 5 that derives basic analysis results and detailed analysis results, and an accuracy determination unit 6 that calculates the Fourier spectral ratio of the basic analysis results to the detailed analysis results, determines whether or not the accuracy of the basic analysis results is sufficient based on the Fourier spectral ratio, and resets the basic element size to a smaller value if it is determined that the accuracy is insufficient.When the basic element size is reset, the mesh division unit 3 mesh-divides the stratum model using the reset basic element size to re-create the basic mesh model, and the earthquake motion analysis unit 5 estimates earthquake motion for the re-created basic mesh model to re-derive the basic analysis results. According to the above-mentioned configuration, the geological layer model creation unit 2 creates a geological layer model based on the ground structure of the area to be analyzed. This geological layer model is meshed by the mesh division unit 3 with a basic element size whose initial value is determined based on the period of the earthquake to be analyzed, and a basic mesh model is generated. In the earthquake motion analysis unit 5, the earthquake source model created by the earthquake source model creation unit 4 based on the earthquake source characteristics is applied to the basic mesh model, earthquake motion is estimated by finite element method analysis, and a basic analysis result is derived. In this configuration, considering the processing time required for the analysis, it is desirable to make the basic element size as large as possible and reduce the number of elements that make up the basic mesh model, but on the other hand, if the basic element size is made too large, the analysis accuracy may be reduced. Here, when creating the basic mesh model, the mesh division unit 3 simultaneously divides the stratum model into meshes with a detailed element size smaller than the basic element size to create a detailed mesh model, and the earthquake motion analysis unit 5 applies the earthquake source model to the detailed mesh model to estimate earthquake motion and derive a detailed analysis result. Since the detailed mesh model is divided into meshes with a detailed element size smaller than the basic element size, it has a smaller element size and a larger number of elements than the basic mesh model divided into meshes with the basic element size. Therefore, the detailed analysis result, which is the analysis result for this detailed mesh model, has a higher analysis accuracy than the basic analysis result. Therefore, if the basic analysis result is compared with the detailed analysis result having a higher analysis accuracy as described above, it is possible to efficiently determine whether the accuracy of the basic analysis result is insufficient. In the above configuration, the accuracy determination unit 6 calculates the Fourier spectrum ratio of the basic analysis result to the detailed analysis result, and based on this, determines whether the accuracy of the basic analysis result is sufficient. Therefore, it is possible to efficiently determine whether the accuracy of the basic analysis result is sufficient. If the accuracy determination unit 6 determines that the accuracy is insufficient, the basic element size is reset to a smaller value. Then, the mesh division unit 3 divides the stratum model into meshes using the basic element size reset to a smaller value to create a basic mesh model again, and the earthquake motion analysis unit 5 applies the earthquake source model to the re-created basic mesh model to estimate earthquake motion and derive the basic analysis result again. Since the re-created basic mesh model is divided into meshes using the basic element size reset to a smaller value, it has a smaller element size and a larger number of elements than the previous basic mesh model before it was re-created. Therefore, the basic analysis result of this re-created basic mesh model has higher analysis accuracy than the basic analysis result of the previous basic mesh model that was previously analyzed and determined to be insufficient in accuracy. Furthermore, while reducing the basic element size as described above, if it is determined that the accuracy of the basic analysis results is sufficient, the basic element size can be configured not to be reset to a smaller value, thereby preventing the basic element size from becoming excessively small and the basic mesh model from being divided into excessively fine meshes. In this way, the geological model is divided into meshes with more appropriate element sizes, and as a result, the analysis accuracy can be increased to a certain level or higher.

[0043] In addition, the earthquake source model creation unit 4 creates multiple earthquake source models based on statistical values ​​of the earthquake source characteristics, and the earthquake motion analysis unit 5 estimates earthquake motion multiple times by sequentially applying each of the multiple earthquake source models, and the earthquake motion analysis unit 5 estimates earthquake motion for both the basic mesh model and the detailed mesh model and derives basic analysis results and detailed analysis results only when the first earthquake source model among the multiple earthquake source models is applied to estimate earthquake motion for the first time, and in other cases, estimates earthquake motion only for the latest basic mesh model and derives basic analysis results, and the accuracy assessment unit 6 assesses the accuracy of the basic analysis results and resets the basic element size only when the first earthquake source model is applied to estimate earthquake motion. In general, source characteristics are created by performing inversion based on observation records of past earthquakes to estimate source characteristics equivalent to these. If statistical values ​​such as average values ​​and variations (standard deviations) are known or estimated for each characteristic, multiple values ​​can be set for each characteristic according to the range of variation. Therefore, multiple source models can be created based on the statistical values ​​of source characteristics. According to the above configuration, the earthquake source model creation unit 4 creates multiple earthquake source models based on the statistics of the earthquake source characteristics, and the earthquake motion analysis unit 5 estimates earthquake motion multiple times by sequentially applying each of the multiple earthquake source models. Therefore, it is possible to estimate earthquake motion taking into account the statistics of the earthquake source characteristics. Here, the earthquake motion analysis unit 5 estimates earthquake motion multiple times by sequentially applying each of the multiple earthquake source models. Therefore, if earthquake motions of both the basic mesh model and the detailed mesh model are estimated for each of the multiple earthquake source models as described above, a significant amount of analysis time will be required. However, in estimating earthquake motion using a detailed mesh model, the purpose is to compare the detailed analysis results with the basic analysis results of the basic mesh model to determine whether the accuracy of the basic analysis results is sufficient, and to adjust the basic element size to be smaller when meshing the basic mesh model as necessary. Therefore, once the basic element size is set appropriately small enough to determine that the accuracy of the basic analysis results is sufficient in an analysis applying the first of multiple earthquake source models, and the basic mesh model is appropriately meshed, in subsequent analyses applying the second and subsequent earthquake source models, if the same basic mesh model meshed with the same basic element size is used to estimate earthquake motion, it can be generally guaranteed that the accuracy of the basic analysis results will be sufficient in the subsequent analyses. Furthermore, when it is determined in an analysis applying the first of multiple seismic source models that the accuracy of the basic analysis results is insufficient, the basic mesh model is re-created to estimate seismic motion, the basic analysis results are re-derived and compared with the detailed analysis results, and this process is repeated until it is determined that the accuracy of the basic analysis results is sufficient. Even if this is repeated, the detailed analysis results should basically have high analytical accuracy when they are created for the first time, so there is little need to re-create the detailed mesh model and estimate seismic motion. Based on this idea, in the above configuration, the earthquake motion analysis unit 5 estimates earthquake motion for both the basic mesh model and the detailed mesh model only when the first earthquake motion is estimated by applying the first earthquake motion model among the multiple earthquake motion models, and derives the basic analysis result and the detailed analysis result. That is, when the first earthquake motion model is applied to estimate earthquake motion for the second or subsequent times, the earthquake motion analysis unit 5 does not estimate earthquake motion for the detailed mesh model. Also, when estimating earthquake motion by applying an earthquake motion model other than the first earthquake motion model, the earthquake motion analysis unit 5 does not estimate earthquake motion for the detailed mesh model, but estimates earthquake motion only for the latest basic mesh model that was generated last and was determined to have sufficient accuracy of the basic analysis result as a result of estimating earthquake motion by applying the first earthquake motion model, and derives the basic analysis result. In this way, it is possible to reduce the number of times earthquake motion is estimated for the detailed mesh model, thereby reducing the analysis time, while maintaining a certain level of analysis accuracy when all earthquake motion models are applied.

[0044] The initial value of the basic element size is the wavelength of the earthquake to be analyzed divided by a value between 5 and 10, and the detailed element size is half that value. It is generally known that mesh division using an element size obtained by dividing the wavelength of an earthquake by 5 improves the accuracy of analysis. According to the above-mentioned configuration, the upper limit of the initial value of the basic element size before being reset in the subsequent processing is the wavelength of the earthquake to be analyzed divided by 5, so that the accuracy judgment unit 6 is more likely to judge that the accuracy is sufficient in the initial judgment of whether the accuracy of the basic analysis result is sufficient. Therefore, the number of times that a series of processes is executed, which includes resetting the basic element size to a smaller value, mesh-dividing the stratum model with this reset basic element size, recreating the basic mesh model, estimating the earthquake motion for the re-created basic mesh model, and re-deriving the basic analysis result, is reduced. Furthermore, by setting the detailed element size to half the initial value of the basic element size, the detailed element size can be made sufficiently small to ensure sufficiently high accuracy of the detailed analysis results for the detailed mesh model, which are used as a comparison target to ensure the accuracy of the basic analysis results for the basic mesh model. Here, the basic element size for dividing the basic mesh model into meshes should be larger than the detailed element size for dividing the detailed mesh model into meshes. In the above case, since the upper limit of the initial value of the basic element size is the value obtained by dividing the wavelength of the earthquake by 5, the detailed element size at its maximum will be 1 / 2 of that value, i.e., the value obtained by dividing the wavelength of the earthquake by 10. In other words, by setting the lower limit of the initial value of the basic element size to the value obtained when the detailed element size is at its maximum, the initial value of the basic element size will be smaller than the value that can be adopted as the detailed element size, and the basic mesh model will be prevented from being divided into excessively small meshes.

[0045] [Modification of the first embodiment] The earthquake motion analysis system 1 of the present invention is not limited to the above-mentioned first embodiment explained with reference to the drawings, and various other modified examples are conceivable within the technical scope of the system. For example, in the first embodiment, the first earthquake source model is applied to estimate earthquake motion, and if the accuracy of the basic analysis result is not judged to be sufficient, only the basic element size is reset to a smaller value and only the basic mesh model is created again. That is, in the first embodiment, the detailed mesh model is fixed to the one created initially, and the basic mesh model is continuously updated so that the basic element size becomes finer, but this is not limited to the above.

[0046] For example, when the accuracy determination unit 6 determines that the accuracy is insufficient when applying the first earthquake source model to estimate seismic motion, the accuracy determination unit 6 may change the basic element size to a value smaller than the currently set value and also change the detailed element size to a value smaller than the currently set value. Then, the mesh division unit 3 performs mesh division based on the reset basic element size and detailed element size to create a new basic mesh model and a new detailed mesh model, respectively.

[0047] Then, the earthquake motion analysis unit 5 applies the first earthquake source model to estimate earthquake motion for both the newly created basic mesh model and the newly created detailed mesh model. Then, the accuracy determination unit 6 compares the newly obtained basic analysis result with the newly obtained detailed analysis result to determine the accuracy of the basic analysis result. Specifically, for example, when applying a first seismic source model to estimate seismic motion, an analysis is performed on a basic mesh model with a basic element size of 500 and a detailed mesh model with a detailed element size of 250. If it is determined that the accuracy of the basic analysis results is insufficient, the next analysis may be performed on a basic mesh model with a basic element size of 450 and a detailed mesh model with a detailed element size of 200. When applying the first source model to estimate seismic motion, the above process can be repeated until it is determined that the accuracy is sufficient, allowing the basic mesh model to be meshed with an appropriate element size.

[0048] According to the above-mentioned configuration, the earthquake source model creation unit creates a plurality of earthquake source models based on the statistical values ​​of the earthquake source characteristics, the earthquake motion analysis unit estimates earthquake motion a plurality of times by sequentially applying each of the plurality of earthquake source models, the earthquake motion analysis unit estimates earthquake motion for both the basic mesh model and the detailed mesh model and derives basic analysis results and detailed analysis results only when estimating earthquake motion by applying a first earthquake source model among the plurality of earthquake source models, and when estimating earthquake motion by applying an earthquake source model other than the first earthquake source model, the earthquake motion analysis unit estimates earthquake motion only for the latest basic mesh model and derives basic analysis results, and the accuracy determination unit determines that the accuracy is insufficient. If so, the basic element size is reset to a smaller value and the detailed element size is reset to a smaller value, and only when the first seismic source model is applied to estimate seismic motion, is the accuracy of the basic analysis results judged and the basic element size and detailed element size reset; if the basic element size and detailed element size are reset, the mesh division unit meshes the stratum model using the reset basic element size and detailed element size to recreate the basic mesh model and detailed mesh model, respectively, and the seismic motion analysis unit estimates seismic motion for the recreated basic mesh model and detailed mesh model to re-derive the detailed analysis results. It goes without saying that this modified example provides the same effects as the first embodiment already described.

[0049] [Second embodiment] Next, a second embodiment will be described. Here, only the parts of the second embodiment that are different from the first embodiment will be described. In the second embodiment, when the accuracy is determined to be insufficient in estimating earthquake motion by applying the first earthquake source model, the accuracy determination unit 6 resets the basic element size to the value of the detailed element size at that time, and changes the detailed mesh model to the basic mesh model. Furthermore, the accuracy determination unit 6 changes the detailed element size to a value smaller than the currently set value. Then, the mesh division unit 3 performs mesh division based on the reset detailed element size to create a new detailed mesh model.

[0050] Then, the earthquake motion analysis unit 5 applies the first earthquake source model to estimate earthquake motion only for the newly created detailed mesh model. Since the basic mesh model at this stage is the same as the detailed mesh model in the previous analysis, it is not necessary to estimate earthquake motion again for this basic mesh model, and the detailed analysis result in the previous analysis can be used as the analysis result of the basic mesh model. Then, the accuracy determining unit 6 compares the basic analysis result, that is, the detailed analysis result in the previous analysis, with the newly obtained detailed analysis result to determine the accuracy of the basic analysis result. Specifically, for example, when estimating seismic motion by applying the first seismic source model, an analysis is performed on a basic mesh model with a basic element size of 500 and a detailed mesh model with a detailed element size of 250, and if it is determined that the accuracy of the basic analysis results is insufficient, the next analysis is performed on a detailed mesh model with a detailed element size smaller than 250, for example, 200. In this case, the basic element size of the basic mesh model will be 250, which is the detailed element size in the previous analysis, but since the analysis corresponding to this has been performed as the detailed mesh model in the previous analysis, it is not necessary to perform it again. When applying the first source model to estimate seismic motion, the above process can be repeated until it is determined that the accuracy is sufficient, allowing the basic mesh model to be meshed with an appropriate element size.

[0051] The earthquake motion analysis system 1 as described above is an earthquake motion analysis system 1 for estimating earthquake motion, and includes a geological layer model creation unit 2 for creating a geological layer model based on the ground structure of an area to be analyzed, a mesh division unit 3 for dividing the geological layer model into meshes using a basic element size whose initial value is determined based on the period of the earthquake to be analyzed and a detailed element size smaller than the basic element size to create a basic mesh model and a detailed mesh model, a seismic source model creation unit 4 for creating a seismic source model based on seismic source characteristics, a seismic source model application unit 5 for applying the seismic source model to each of the basic mesh model and the detailed mesh model to estimate earthquake motion by finite element method analysis and derive a basic analysis result and a detailed analysis result, and and an accuracy determination unit 6 that calculates a Fourier spectral ratio of the analysis result, determines whether or not the accuracy of the basic analysis result is sufficient based on the Fourier spectral ratio, and if it is determined that the accuracy is insufficient, resets the basic element size to a smaller value. If the basic element size is reset, the accuracy determination unit 6 resets the basic element size to the value of the detailed element size, changes the detailed mesh model to a basic mesh model, and resets the detailed element size to a smaller value. The mesh division unit 3 mesh-divides the stratum model based on the reset detailed element size to re-create a detailed mesh model. The earthquake motion analysis unit 5 estimates earthquake motion for the re-created detailed mesh model, and re-derives the detailed analysis results. According to the above-mentioned configuration, the geological layer model creation unit 2 creates a geological layer model based on the ground structure of the area to be analyzed. This geological layer model is meshed by the mesh division unit 3 with a basic element size whose initial value is determined based on the period of the earthquake to be analyzed, and a basic mesh model is generated. In the earthquake motion analysis unit 5, the earthquake source model created by the earthquake source model creation unit 4 based on the earthquake source characteristics is applied to the basic mesh model, earthquake motion is estimated by finite element method analysis, and a basic analysis result is derived. In this configuration, considering the processing time required for the analysis, it is desirable to make the basic element size as large as possible and reduce the number of elements that make up the basic mesh model, but on the other hand, if the basic element size is made too large, the analysis accuracy may be reduced. Here, when creating the basic mesh model, the mesh division unit 3 simultaneously divides the stratum model into meshes with a detailed element size smaller than the basic element size to create a detailed mesh model, and the earthquake motion analysis unit 5 applies the earthquake source model to the detailed mesh model to estimate earthquake motion and derive a detailed analysis result. Since the detailed mesh model is divided into meshes with a detailed element size smaller than the basic element size, it has a smaller element size and a larger number of elements than the basic mesh model divided into meshes with the basic element size. Therefore, the detailed analysis result, which is the analysis result for this detailed mesh model, has a higher analysis accuracy than the basic analysis result. Therefore, if the basic analysis result is compared with the detailed analysis result having a higher analysis accuracy as described above, it is possible to efficiently determine whether the accuracy of the basic analysis result is insufficient. In the above configuration, the accuracy determination unit 6 calculates the Fourier spectrum ratio of the basic analysis result to the detailed analysis result, and based on this, determines whether the accuracy of the basic analysis result is sufficient. Therefore, it is possible to efficiently determine whether the accuracy of the basic analysis result is sufficient. If the accuracy determination unit 6 determines that the accuracy is insufficient, the basic element size is reset to a smaller value, such as the value of the detailed element size at the current stage. Then, the detailed mesh model is changed to the basic mesh model. Since this basic mesh model is the same as the detailed mesh model, the basic analysis result can be the same as the detailed analysis result at this point in time. The accuracy determination unit 6 also resets the detailed element size to a smaller value, and the mesh division unit 3 mesh-divides the stratum model with the reset detailed element size to create a detailed mesh model again, and the earthquake motion analysis unit 5 estimates earthquake motion for the detailed mesh model created again to derive the detailed analysis result again. In this way, both the basic mesh model and the detailed mesh model are mesh-divided finer than the basic mesh model and the detailed mesh model at the time when the accuracy determination unit 6 determined that the accuracy was insufficient. Therefore, the accuracy of the basic analysis result and the detailed analysis result corresponding to each of them is improved, and the possibility of determining that the accuracy of the basic analysis result is sufficient increases. Furthermore, while reducing the basic element size as described above, if it is determined that the accuracy of the basic analysis results is sufficient, the basic element size can be configured not to be reset to a smaller value, thereby preventing the basic element size from becoming excessively small and the basic mesh model from being divided into excessively fine meshes. In this way, the geological model is divided into meshes with an appropriate element size, and as a result, the analysis accuracy can be increased to a certain level or higher.

[0052] Further, the seismic source model creation unit creates a plurality of seismic source models based on the statistical values ​​of the seismic source characteristics, and the earthquake motion analysis unit estimates earthquake motion a plurality of times by sequentially applying each of the plurality of seismic source models, and the earthquake motion analysis unit estimates earthquake motion for both the basic mesh model and the detailed mesh model and derives basic analysis results and detailed analysis results only when applying a first seismic source model among the plurality of seismic source models to estimate earthquake motion for the first time, estimates earthquake motion only for the detailed mesh model and derives detailed analysis results when applying the first seismic source model to estimate earthquake motion for the second or subsequent times, and estimates earthquake motion for only the detailed mesh model and derives detailed analysis results when applying a seismic source model other than the first seismic source model to estimate earthquake motion. The accuracy determination unit estimates seismic motion only for the model and derives basic analysis results, and the accuracy determination unit determines the accuracy of the basic analysis results only when the first seismic source model is applied to estimate seismic motion, and if it is determined that the accuracy is insufficient, the basic element size is reset to the value of the detailed element size, the detailed mesh model is changed to the latest basic mesh model, and the detailed element size is reset to a smaller value, and if the detailed element size is reset, the mesh division unit meshes the stratum model using the reset detailed element size to re-create the detailed mesh model, and the seismic motion analysis unit estimates seismic motion for the re-created detailed mesh model and re-derives the detailed analysis results. With this configuration, the analysis precision can be increased to a certain level or higher.

[0053] Note that the first embodiment, the modified example of the first embodiment, and the second embodiment differ in that when the accuracy is determined to be insufficient when applying the first seismic source model to estimate seismic motion, the basic mesh model and detailed mesh model to be used in the next analysis are different. For example, in the second embodiment, the basic element size is the detailed element size in the previous analysis, so that the mesh division of the basic mesh model is significantly finer. Therefore, it is possible to determine the basic element size quickly and proceed to the analysis of the second and subsequent earthquake source models at an early stage. However, the mesh division of the basic mesh model is significantly finer, which means that, in other words, even if mesh division is performed with a larger basic element size, there is a possibility that a sufficiently accurate analysis result can be achieved, but this possibility is not considered. Therefore, the basic element size becomes smaller than necessary, and the basic mesh model is meshed excessively finely, so that it may take a long time to analyze the second and subsequent earthquake source models. Therefore, it is desirable to appropriately determine whether to adopt the first embodiment, the modified example of the first embodiment, or the second embodiment, depending on circumstances such as the total number of earthquake source models and the extent to which the Fourier spectrum ratio in the accuracy determination unit 6 deviates from the lower threshold LB or the upper threshold UB.

[0054] In addition to the above-described first embodiment, the modified example of the first embodiment, and the second embodiment, it is possible to select from the configurations given in these, or to change to other configurations as appropriate. [Explanation of symbols]

[0055] 1 Earthquake motion analysis system 5 Earthquake motion analysis section 2 Strata model creation section 6 Accuracy assessment section 3 Mesh division section 7 Post-processing section 4. Earthquake source model creation section

Claims

1. A seismic motion analysis system for estimating seismic motion, comprising: a geological model creation unit that creates a geological model based on the ground structure of an area to be analyzed; a mesh division unit that divides the stratum model into meshes using a basic element size, the initial value of which is determined based on the period of an earthquake to be analyzed, and a detailed element size smaller than the basic element size, to create a basic mesh model and a detailed mesh model; a source model creation unit that creates a source model based on the source characteristics; a seismic motion analysis unit that applies the seismic source model to each of the basic mesh model and the detailed mesh model, estimates the seismic motion by a finite element method analysis, and derives a basic analysis result and a detailed analysis result; an accuracy determination unit that calculates a Fourier spectrum ratio of the basic analysis result to the detailed analysis result, determines whether or not the accuracy of the basic analysis result is sufficient based on the Fourier spectrum ratio, and resets the basic element size to a smaller value when it is determined that the accuracy is insufficient; Equipped with When the basic element size is reset, the mesh division unit divides the stratum model into meshes using the reset basic element size to create the basic mesh model again, and the earthquake motion analysis unit estimates the earthquake motion for the re-created basic mesh model to again derive the basic analysis result. The earthquake motion analysis system is characterized by the above.

2. the earthquake source model creation unit creates a plurality of the earthquake source models based on statistics of earthquake source characteristics, and the earthquake motion analysis unit estimates the earthquake motion a plurality of times by sequentially applying each of the plurality of the earthquake source models; the earthquake motion analysis unit estimates the earthquake motion for both the basic mesh model and the detailed mesh model and derives the basic analysis result and the detailed analysis result only when the first earthquake motion is estimated by applying the first earthquake motion model among the plurality of earthquake motion models, and in other cases, estimates the earthquake motion only for the latest basic mesh model and derives the basic analysis result; The accuracy determination unit determines the accuracy of the basic analysis result and resets the basic element size only when the first seismic source model is applied to estimate the seismic motion.

2. The earthquake motion analysis system according to claim 1 .

3. The initial value of the basic element size is a value obtained by dividing the wavelength of the earthquake to be analyzed by a value equal to or greater than 5 and less than 10, and the detailed element size is a value half the value.

3. The earthquake motion analysis system according to claim 1 or 2.

4. A seismic motion analysis system for estimating seismic motion, comprising: a geological model creation unit that creates a geological model based on the ground structure of an area to be analyzed; a mesh division unit that divides the stratum model into meshes using a basic element size, the initial value of which is determined based on the period of an earthquake to be analyzed, and a detailed element size smaller than the basic element size, to create a basic mesh model and a detailed mesh model; a source model creation unit that creates a source model based on the source characteristics; a seismic motion analysis unit that applies the seismic source model to each of the basic mesh model and the detailed mesh model, estimates the seismic motion by a finite element method analysis, and derives a basic analysis result and a detailed analysis result; an accuracy determination unit that calculates a Fourier spectrum ratio of the basic analysis result to the detailed analysis result, determines whether or not the accuracy of the basic analysis result is sufficient based on the Fourier spectrum ratio, and resets the basic element size to a smaller value when it is determined that the accuracy is insufficient; Equipped with When the basic element size is reset, the accuracy determination unit resets the basic element size to the value of the detailed element size, changes the detailed mesh model to the basic mesh model, and resets the detailed element size to a smaller value, the mesh division unit mesh-divides the stratum model using the reset detailed element size to create the detailed mesh model again, and the earthquake motion analysis unit estimates the earthquake motion for the re-created detailed mesh model, and derives the detailed analysis result again. The earthquake motion analysis system is characterized by the above.

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