Earthquake risk assessment method and system for medium-strong earthquake area

Abstract

The invention provides an earthquake risk assessment method and system for a medium-strong earthquake region, and belongs to the technical field of earthquake risk assessment, and the method comprises the steps: carrying out the partitioning construction of an earthquake region, and obtaining a plurality of structural regions; fitting data of historical earthquakes and modern small and medium earthquakes in each structural area to obtain an earthquake magnitude-frequency relational expression, and calculating to obtain an incidence rate, an earthquake generation probability and a recurrence interval of any level of earthquake in each structural area; and for each structural area, a spatial smoothing method is used to distribute weights such as the occurrence rate, the earthquake generation probability and the recurrence interval of any grade of earthquake in each earthquake grade, and the like, to each fault zone. According to the method, the seismic activity model is established by using the spatial smoothing method, after smoothing processing, the earthquake risk is generally improved and is close to the historical earthquake occurrence situation, and for the areas with unclear earthquake-generating structures and weak seismic activities, the earthquake with large energy release occupies a more important position in distribution, so that the seismic activity is improved. And the potential danger of the earthquake activity can be reflected more accurately.

Description

Technical Field

[0001] The present invention relates to the technical field of seismic hazard assessment, and more particularly to a method and system for seismic hazard assessment in moderately strong earthquake regions. Background Art

[0002] For moderately strong earthquake active regions, the largest historical earthquake is less than magnitude 7. Modern seismic activities are scarce and there is no obvious zonation. Earthquakes do not match well with existing faults. Due to the positioning errors of historical earthquakes, the position matching degree between historical earthquakes and faults is generally poor, resulting in a deviation between the spatial distribution of earthquakes and the actual situation, unclear seismogenic structures, inaccurate magnitude judgment, and thus affecting the calculation of seismic energy. For fault zones, the accumulated stress and released energy are important indicators for assessing hazards. If the conventional seismic activity statistical method is used to evaluate the fault hazard, due to the positioning error, the energy released by earthquakes near the fault is underestimated, and it will be wrongly considered that the stress accumulation and release level of this fault is relatively low, thus reducing the assessment of its hazard. Summary of the Invention

[0003] Therefore, an object of the present invention is to provide a method and system for seismic hazard assessment in moderately strong earthquake regions to solve the problems mentioned in the background art and overcome the deficiencies in the prior art.

[0004] To achieve the above object, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a method for seismic hazard assessment in moderately strong earthquake regions, including: Performing zonal tectonics on the earthquake region to obtain multiple tectonic regions; Fitting the historical earthquake and modern small and medium earthquake data in each tectonic region to obtain a magnitude-frequency relationship formula, and calculating the occurrence rate, seismogenic probability, and recurrence interval of any magnitude earthquake in each tectonic region; Using the spatial smoothing method in each tectonic region to distribute the weights of each magnitude bin, the occurrence rate, seismogenic probability, and recurrence interval of any magnitude earthquake in each tectonic region to each fault zone.

[0005] Preferably, the step of using the spatial smoothing method in each tectonic region to distribute the weights of each magnitude bin, the occurrence rate, seismogenic probability, and recurrence interval of any magnitude earthquake in each tectonic region to each fault zone includes: Statistically organize the historical destructive earthquake catalog and the regional network earthquake catalog of the tectonic area, determine the magnitude bins to be allocated for each tectonic area, calculate the annual occurrence rate of earthquakes at all levels in the tectonic area according to the magnitude-frequency relationship, divide the tectonic area into uniform grids, calculate the seismicity of each grid as the weight, use the moving average method to calculate the average value of the seismicity in adjacent grids to smooth the data, and then, based on the weight and without exceeding the maximum potential magnitude, allocate the occurrence rate, occurrence probability, recurrence interval, etc. of earthquakes at each magnitude bin and any level in each tectonic area to each fault zone.

[0006] Preferably, the division of the tectonic area into uniform grids includes: dividing the tectonic area into grids of 0.1°×0.1° in the longitude and latitude directions.

[0007] Preferably, the magnitude-frequency relationship is as follows: where is the annual occurrence rate of earthquakes of magnitude is the magnitude, is the seismic activity constant, is the relative proportion coefficient.

[0008] Preferably, the formula for calculating the seismicity is as follows:

[0009] where is the seismicity / seismic radiation energy, is the comprehensive magnitude of the tectonic area.

[0010] Preferably, the method further includes: determining the maximum potential magnitude of each tectonic area according to the historical seismic activity, current seismic activity and the nature of the faults in the tectonic area; including the maximum potential magnitude of the fault zone in the tectonic area with the activity era of early and middle Pleistocene, the maximum potential magnitude of the fault zone in the tectonic area with the activity era of late Pleistocene, and the maximum potential magnitude of the fault zone in the tectonic area with the activity era before Quaternary.

[0011] Preferably, the principle for determining the maximum potential magnitude of the fault zone in the tectonic area with the activity era of early and middle Pleistocene is as follows: If there is a fault intersection in the fault zone in the tectonic area, the activity nature of the fault is a strike-slip fault, the deep background of the fault is the edge of the depression and uplift, and the maximum magnitude of historical earthquakes is greater than or equal to 6, the maximum magnitude of current small earthquakes is greater than or equal to 4, and the length of the fault zone is greater than or equal to 30 km, then the maximum potential magnitude of the fault zone in the tectonic area with the activity era of early Pleistocene and the maximum potential magnitude of the fault zone in the tectonic area with the activity era of middle Pleistocene are 6.5; If the fault zone in the tectonic area belongs to non-fault intersection, the activity nature of the fault is normal fault or reverse fault, the deep background of the fault is the edge of non-sag uplift, the maximum magnitude of historical earthquakes is greater than or equal to 5, the maximum magnitude of current small earthquakes is greater than or equal to 3, and the length of the fault zone is less than 30 kilometers, then the maximum potential magnitude of the fault zone activity in the tectonic area in the early Pleistocene and the maximum potential magnitude of the fault zone activity in the tectonic area in the middle Pleistocene are 6.0.

[0012] Preferably, the principle for determining the maximum potential magnitude of the fault zone activity in the tectonic area in the late Pleistocene is as follows: Calculate and determine the maximum potential magnitude of the fault zone activity in the tectonic area in the late Pleistocene through the regression relationship formula.

[0013] Preferably, the principle for determining the maximum potential magnitude of the fault zone activity in the tectonic area before the Quaternary is as follows: Determine according to the background magnitude of the seismic zone.

[0014] In a second aspect, the present invention provides a medium-strong earthquake area seismic hazard assessment system, including: A zoning structure module: used for zoning the seismic area to obtain multiple tectonic areas; A fitting calculation module: used for fitting the historical earthquake and modern small and medium earthquake data in each tectonic area to obtain a magnitude-frequency relationship curve, and calculating the occurrence rate, seismogenic probability and recurrence interval of any magnitude earthquake in each tectonic area; An equal-weight distribution module: using the spatial smoothing method to equally distribute the weights of each magnitude range, the occurrence rate, seismogenic probability and recurrence interval of any magnitude earthquake in each tectonic area to each fault zone in each tectonic area.

[0015] In a third aspect, the present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the steps of a medium-strong earthquake area seismic hazard assessment method as described above are implemented.

[0016] In a fourth aspect, the present invention provides a readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of a medium-strong earthquake area seismic hazard assessment method as described above are implemented.

[0017] Therefore, the present invention has the following beneficial effects: A method and system for seismic hazard assessment in moderately strong earthquake regions of the present invention establish a seismic activity model using a spatial smoothing method. First, the seismic hazard of the tectonic region is statistically analyzed, and then it is smoothed according to the energy released by earthquakes. Using the energy released by historical earthquakes on the fault zone as weights, the seismic hazard data is distributed to each fault. After smoothing, the seismic hazard generally increases and is closer to the historical earthquake occurrence. For areas where the seismogenic structure is unclear and seismic activity is relatively weak, earthquakes with larger energy releases play a more important role in the distribution, and the potential seismic hazard can be more accurately reflected.

[0018] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, where: Figure 1 is the overall flowchart of the method of the present invention; Figure 2 is the seismic tectonic zoning map of the embodiment of the present invention; Figure 3 is the comprehensive assessment map of seismic hazard of the main faults in a certain province in the embodiment of the present invention; Figure 4 is the schematic diagram of the system structure connection relationship of the embodiment of the present invention; Figure 5 is the schematic diagram of the computer device structure of the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0021] The definition of seismic risk assessment for active faults in "Active Fault Detection (GB / T 36072 - 2018)" is: the process of judging the segments (locations), maximum possible earthquakes and risks of medium or stronger earthquakes occurring on active faults within a certain future time. A relatively detailed assessment method is given for active faults with surface-exposed traces, but no operational assessment method is given for buried faults. It only states that "Based on the geometric structure of active faults, the distribution of historical earthquake damage areas, the distribution of current earthquake epicenters, the geophysical field, the relationship between shallow and deep structures, etc., divide the fault rupture segments with the risk of medium or stronger earthquakes, and comprehensively evaluate the magnitude of the maximum possible earthquake." "The seismic risk of each active segment of the fault should be evaluated based on data such as the spatio-temporal migration of regional earthquakes, magnitude-time images, active and quiet stages, etc." In the seismic risk assessment of active faults, how to consider the complexity of earthquake recurrence behavior, especially for high-magnitude earthquakes, is a key issue. However, there is currently no unified understanding of the recurrence behavior of large earthquakes. The early characteristic earthquake model believed that: the small and medium earthquakes on the fault zone preferably follow the GR exponential model (Gutenberg and Richter, 1956); while the frequency of large earthquakes significantly deviates from the magnitude-frequency relationship curve obtained by fitting small and medium earthquake data, that is, large earthquakes are characteristic, and extrapolating the GR relationship obtained from small and medium earthquakes will underestimate the occurrence frequency of large earthquakes.

[0022] For late Pleistocene active faults and fault segments with historical strong earthquake activities or relatively frequent modern small and medium earthquake activities, seismic risk assessment should be carried out as much as possible using statistical methods based on geological data and earthquake activities in seismic tectonic sub-areas; while for the seismic risk assessment of active faults in the middle Pleistocene and pre-Quaternary activities that have been determined, it is mainly based on the statistical method of moderate and strong earthquake activities in seismic tectonic sub-areas for evaluation.

[0023] Due to the positioning error of historical earthquakes, the position matching degree between historical earthquakes and faults is generally poor. Directly using the statistical method of earthquake activities in seismic tectonic sub-areas will greatly reduce the risk degree of faults.

[0024] As Figure 1 shown, the present invention provides a method for seismic risk assessment in moderately strong earthquake areas, including: Conducting zonal tectonics on the earthquake area to obtain multiple tectonic areas; Fitting the historical earthquake and modern small and medium earthquake data in each tectonic area to obtain the magnitude-frequency relationship formula, and calculating the occurrence rate, seismogenic probability and recurrence interval of any magnitude earthquake in each tectonic area; Using the spatial smoothing method in each tectonic area to allocate the weights of the occurrence rate, seismogenic probability and recurrence interval of any magnitude earthquake in each magnitude range and each tectonic area to each fault zone.

[0025] The magnitude-frequency relationship curve obtained by fitting historical earthquakes and modern small and medium-sized earthquakes in the constructed area in the present invention, considering the inaccuracy of historical earthquake location and the insufficient time scale of modern earthquakes, distributes the average annual incidence rate of seismic activities to each fault by means of smooth weighting, obtaining the average annual incidence rate, average recurrence interval of each fault, and the probabilities of at least one earthquake occurring in the next 50 years, 100 years, and 200 years.

[0026] In order to better conduct seismic tectonic zoning in the study area, the present invention first studies the basic characteristics of Quaternary active faults in the region; analyzes the tectonic units to which they belong, the directions of the faults, and the main tectonic frameworks of the tectonic regions.

[0027] Secondly, in order to identify the activities of the main faults in the study area, collect the research results of the faults in the study area, the results of active fault mapping, urban active fault detection, seismic safety evaluation reports, and paper journal results, determine the geometric structure and distribution of the faults, and preliminarily judge the activity and the latest activity time of the faults.

[0028] Based on aspects such as seismic activities, seismic tectonics, deep geophysics, and tectonic stress fields, summarize and give the basis and principles for the division of seismic tectonic zoning: The tectonic zoning should include earthquakes above magnitude 6 to facilitate the statistics of the annual incidence rate of earthquakes of magnitude 6 and above; the extension directions of the seismic tectonics should be generally consistent; there should be no large geomagnetic and gravity gradient zones in the tectonic area in terms of deep geophysics; there should be a relatively unified tectonic stress field direction. In different seismic tectonic areas, a complete analysis of seismic data at different time periods should also be carried out to determine the time period and magnitude range of the statistical earthquakes.

[0029] The present invention discriminates the seismogenic structures of the main faults in the region again and determines the maximum potential earthquakes.

[0030] Specifically, according to the historical seismic activities, current seismic activities, and the nature of the faults in the tectonic area, determine the maximum potential magnitude of each tectonic area; including the maximum potential magnitude of the fault zone with an active time of early and middle Pleistocene in the tectonic area, the maximum potential magnitude of the fault zone with an active time of late Pleistocene in the tectonic area, and the maximum potential magnitude of the fault zone with an active time before the Quaternary in the tectonic area.

[0031] The determination principle of the maximum potential magnitude of the fault zone with an active time of early and middle Pleistocene in the tectonic area is as shown in Table 1 below.

[0032]

[0033] Specifically, if there is a fracture intersection in the fault zone within the tectonic area, the activity nature of the fault is a strike-slip fault, the deep background of the fracture is the edge of the depression uplift, and the maximum magnitude of historical earthquakes is greater than or equal to 6, the maximum magnitude of current small earthquakes is greater than or equal to 4, and the length of the fault zone is greater than or equal to 30 kilometers, then the maximum potential magnitude of the fault zone activity era in the tectonic area in the early Pleistocene and the maximum potential magnitude of the fault zone activity era in the middle Pleistocene are 6.5; if the fault zone in the tectonic area belongs to non-fracture intersection, the activity nature of the fault is a normal fault or reverse fault, the deep background of the fracture is not the edge of the depression uplift, and the maximum magnitude of historical earthquakes is greater than or equal to 5, the maximum magnitude of current small earthquakes is greater than or equal to 3, and the length of the fault zone is less than 30 kilometers, then the maximum potential magnitude of the fault zone activity era in the tectonic area in the early Pleistocene and the maximum potential magnitude of the fault zone activity era in the middle Pleistocene are 6.0.

[0034] The determination principle of the maximum potential magnitude of the fault zone activity era in the late Pleistocene in the tectonic area is as follows: Calculate and determine the maximum potential magnitude of the fault zone activity era in the late Pleistocene in the tectonic area through the regression relation.

[0035] The discriminant empirical relationship of active structures since the late Pleistocene comprehensively discriminates the maximum potential magnitude according to the empirical relationship between the scale of the fracture and the rupture length of the magnitude, and the empirical relationship between the magnitude - rupture length and rupture area of seismic active faults; the empirical relationship between the scale of the fracture and the rupture length of the magnitude is as follows: Ms = 3.821 + 1.860 * log10(L), Mw = 4.33 + 1.49lg(L), where L is the rupture length, Ms is the surface wave magnitude, and Mw is the moment magnitude.

[0036] The determination principle of the maximum potential magnitude of the fault zone activity era before the Quaternary in the tectonic area is as follows: Determine according to the background magnitude of the seismic zone.

[0037] For faults before the Quaternary, the maximum potential magnitude is no longer divided, and all are considered according to the background magnitude of the seismic zone (5.0 - 5.5 magnitude).

[0038] Fit the historical earthquake and modern small and medium earthquake data in each tectonic area to obtain the magnitude - frequency relation, and calculate the annual occurrence rate, seismogenic probability, and recurrence interval of any magnitude earthquake in each tectonic area.

[0039] The seismogenic probability and recurrence interval can be obtained through the statistics and calculation of historical earthquake and modern small and medium earthquake data in each tectonic area.

[0040] Use the magnitude - frequency relation and Poisson model method to calculate and obtain the annual average occurrence rate of each magnitude earthquake in each seismic tectonic sub - area. The magnitude - frequency relation, and then estimate the reliable constants and of the exponential function segment (i.e., the G - R relation) of this relation: and : 。

[0041] For each tectonic region, the space-smoothing method is used to distribute the weights such as the occurrence rate, the seismogenic probability, and the recurrence interval of earthquakes of each magnitude range and any magnitude within each tectonic region to each fault zone.

[0042] According to the empirical relationship between seismic radiation energy / seismic capacity and magnitude:

[0043] Calculate the seismic capacity of each sub-region where each fault is located. Both historical earthquakes and current earthquakes are uniformly weighted to 500 years. Considering the uncertainty of earthquake location, a smoothing and weighting method is used for each sub-region to calculate the weighted value, and then according to the upper magnitude limit of each fault, the occurrence rate is assigned to each fault.

[0044] Specifically, statistically analyze the historical destructive earthquake catalog and the regional network earthquake catalog of the tectonic region, determine the magnitude ranges to be distributed in each tectonic region, calculate the annual occurrence rate of earthquakes of each level in the tectonic region according to the magnitude-frequency relationship, divide the tectonic region into uniform grids, calculate the seismic activity of each grid as the weight, use the moving average method to calculate the average value of the seismic activity in adjacent grids to smooth the data, and then according to the weight, on the basis of not exceeding the maximum potential magnitude, distribute the weights such as the occurrence rate, the seismogenic probability, and the recurrence interval of earthquakes of each magnitude range and any magnitude within each tectonic region to each fault zone.

[0045] It should be noted that the space-smoothing method of the present invention is the post-space-smoothing method.

[0046] The prior art has proposed a method for establishing a seismicity model using the space-smoothing method, that is, seismicity models established using modern small and medium-sized earthquakes, destructive historical earthquakes, and uniform background earthquakes respectively, and then weighted to determine seismicity parameters. The biggest feature of this method is that it does not divide potential seismic source regions based on the seismic tectonic seismicity model, and can directly use earthquake catalogs to calculate seismic hazards, which is simple and easy to implement.

[0047] Based on the basic assumption that future earthquakes in the space-smoothing model highly concentrate in the regions where past earthquakes occurred, the smoothed seismic activity rate is concentrated in the areas where past earthquakes occurred, and it also basically reflects the activity pattern of future moderate and strong earthquakes. According to the research on the in-situ recurrence rate of moderate and strong earthquakes in South China, when the distance of in-situ recurrence of earthquakes is taken as 50 km, the recurrence rate of earthquakes above magnitude 5 in this region is as high as 61%, which is higher than the national in-situ recurrence rate of strong earthquakes of 53.3%, indicating that the seismic activity of moderate and strong earthquakes in South China has a relatively high in-situ recurrence rate. These results also verify the rationality of using the space-smoothing method to estimate the annual average occurrence rate of earthquakes in this study area.

[0048] The study area is divided into grids of 0.1°×0.1°, and the seismic frequency in each grid is counted. , and then the earthquakes within the grid are smoothed into other spatial grid points through a smoothing function, so as to obtain the seismic occurrence rate in each grid after smoothing:

[0049] In the formula is the smoothing function. The Gaussian smoothing function reflects the spatial inhomogeneity of earthquakes and is more in line with the randomness of earthquake occurrence. is the seismic frequency of each grid, refers to the seismic frequency after smoothing of the th grid, refers to the current th grid, refers to the th grid.

[0050] Using the above method, the annual occurrence rates of earthquakes with M≥4.7 and M≥2.0 in the study area can be calculated. Furthermore, the annual occurrence rates of earthquakes in different magnitude ranges can be derived using the magnitude-frequency relationship. The equal weights of each magnitude range statistically obtained in the study area are distributed to each fault.

[0051] The above-mentioned pre-spatial smoothing method first applies spatial smoothing technology before other analyses or processing of data. Therefore, the pre-spatial smoothing method is highly dependent on the original data, and its effect largely depends on the quality and distribution of the original data. However, modern seismic activities are scarce and there is no obvious zonation. Earthquakes do not match well with existing faults. Due to the historical earthquake location errors, the position matching degree between historical earthquakes and faults is generally poor, resulting in a deviation between the spatial distribution of earthquakes and the actual situation, making the seismogenic structure unclear, leading to inaccurate magnitude judgment, and further affecting the calculation of earthquake energy. The pre-spatial smoothing cannot correct these problems and may even introduce new biases, resulting in a reduction in the assessment of its hazard.

[0052] The difference between the post-spatial smoothing method of the present invention and the above method is that: the post-spatial smoothing method first statistically analyzes the historical destructive earthquake catalog (M≥4.7) and the regional network earthquake catalog (M≥2.0) in the study area (tectonic area), and jointly statistically analyzes the magnitude-frequency relationship formula: Calculate the annual occurrence rates of earthquakes at all levels in the study area , and then calculate the seismic activity degree of each grid as the weight. The formula for seismic activity degree (seismic energy) is: , use the moving average method to calculate the average value within adjacent grids to smooth the data, and then according to the weight, distribute the equal weights of each magnitude range statistically obtained in the study area to each fault. Obtain the recurrence period and seismogenic probability of large earthquakes for each fault.

[0053] Among them, the seismic activity of each grid is calculated as the weight. Assuming the energy of each earthquake is E, the frequency of earthquakes with different magnitudes can be weighted according to the energy size. For example, for a grid area, calculate the weighted earthquake frequency , the weight can be calculated first according to the earthquake energy (where is the total energy of all earthquakes in this area), and then the frequencies of earthquakes with different magnitudes are weighted and summed . This can make earthquakes with larger energy releases play a more important role in frequency statistics and more accurately reflect the potential danger of seismic activity.

[0054] The post-spatial smoothing method of the present invention can specifically handle specific spatial problems that occur in the previous analysis process. Since post-spatial smoothing is performed after other processing, and the previous processing steps have extracted or retained important data information, the post-spatial smoothing method can improve the spatial characteristics of the data on the premise of minimizing the impact on these key information. That is, the present invention first statistically analyzes the seismic hazard of the tectonic area, then smooths it according to the energy released by earthquakes, uses the energy released by historical earthquakes on the fault zone as the weight, distributes the seismic hazard data to each fault, and after the smoothing process, the seismic hazard generally improves and is relatively close to the historical earthquake occurrence situation. For areas where the seismogenic structure is unclear and seismic activity is relatively weak, earthquakes with larger energy releases play a more important role in the distribution and can more accurately reflect the potential danger of seismic activity.

[0055] The following takes the seismic structure exploration project of a certain province as an example to illustrate the method for evaluating the seismic hazard of the moderately strong earthquake area of the present invention.

[0056] The example area belongs to a moderately strong seismic activity area, and appropriate multiple methods need to be selected and compared for the seismic hazard evaluation of faults. For example, the method of estimating the upper magnitude limit using the fault scale or size may not be applicable to all faults, and it is necessary to classify the fault activity (activity era) before carrying out. In addition, the weights of the evaluation methods should be different in areas with sparse small earthquake activities and areas with relatively active seismic activities.

[0057] Most importantly, according to the segmented characteristics and bases of fault activity (including the deep part), combined with the precise location results of small earthquakes, the rupture area and the magnitude size, and combined with tectonic analogy, etc., comprehensively determine the maximum potential seismic capacity of the fault. The extrapolation of the maximum magnitude using the GR relationship is supplemented, and the method of determining the maximum magnitude of a certain structure or tectonic area using tectonic analogy or empirical statistical relationship is the main method.

[0058] ​The whole province is divided into six tectonic regions, among which there is 1 region with a maximum potential magnitude of 7.5, namely the northern Henan sub-region; there are 2 regions with a magnitude of 7.0, namely the northwest Henan and Sanmenxia respectively; and there are 3 regions with a magnitude of 6.5, namely central Henan, eastern Henan, and Qinling-Dabie. The sub-regions are shown in Table 2 below and Figure 2 。

[0059]

[0060] The magnitude interval is taken as 0.3. The starting time of the destructive earthquake catalog is 1484, and the cut-off time for using earthquake catalog data is December 2022. The current catalog of small and medium-sized earthquakes is mainly based on the observation catalog of the China Earthquake Networks Center. The starting time is 1970, and the cut-off time for using earthquake catalog data is December 2022.

[0061] From the fitted magnitude-frequency relationship, relevant parameters of each tectonic sub-region are summarized, and the relationship formula is shown in Table 3.

[0062]

[0063] According to the empirical relationship between seismic radiation energy and magnitude: Calculate the seismic capacity of each small area where the fault is located. Both historical earthquakes and current earthquakes are uniformly weighted to 500 years. Considering the uncertainty of earthquake location, the weight value is calculated for each tectonic region by the method of average smoothing and summation, and then according to the magnitude upper limit of each fault, it is distributed to the occurrence rate of each fault. The results are as Figure 3 shown.

[0064] The beneficial effects of the present invention are also reflected in the following aspects: Clear physical meaning: The calculation of seismic energy is usually carried out through magnitude. For each increase of one magnitude level, the energy approximately increases by 32 times. For example, the energy of a magnitude 5 earthquake is 32 times that of a magnitude 4 earthquake. It is reasonable to use the seismic energy as a smooth statistical parameter, rather than using the number of earthquake occurrences as the statistical parameter in the past.

[0065] Follow the principle of historical earthquake recurrence: Use the magnitudes of historical earthquakes that occurred on the fault zone as weights to intuitively predict the magnitudes of future earthquakes, that is, earthquakes of the same magnitude will occur in the places where historical earthquakes occurred in the past.

[0066] Simplification of quantitative calculation: Previously, it was necessary to first calculate the smoothed values of the number of earthquakes in each grid and each magnitude range, and then statistically calculate the fault hazard, with a large amount of calculation. Now, it is to first statistically calculate the seismic hazard of the tectonic region, and then smooth it according to the seismic energy. The smoothed result is used as a weight to distribute the seismic hazard to each fault, greatly reducing the amount of calculation.

[0067] Improved calculation accuracy: The seismic risk degree of each fracture obtained by the previous calculation methods was generally low. After the smoothing process of the present invention, the seismic risk has generally increased, which is closer to people's subjective understanding and the historical earthquake occurrence situation.

[0068] The existing research methods for earthquake recurrence intervals include the fault-slip method and the seismic moment rate method.

[0069] For the fault-slip method, given the long-term average slip rate of the Holocene fracture segment and the coseismic average displacement of the latest event, the large earthquake recurrence interval can usually be estimated using the formula: , where u is the average coseismic dislocation, which is calculated from the statistical relationship between coseismic dislocation and fault rupture scale; v is the average slip rate of the fault zone, , is the average slip rate of the fracture during a longer period obtained by geological methods, is the average aseismic long-term creep rate on the fracture.

[0070] For the seismic moment rate method, the method of calculating the earthquake recurrence interval using the seismic moment rate has the calculation formula: , where is the characteristic seismic moment, which can be obtained from the quantitative research results of active faults; is the seismic moment rate, which can be obtained from the Brune formula: , where is the shear modulus of the crustal elastic layer, is the fault area, is the fault slip rate.

[0071] Both the fault-slip method and the seismic moment rate method, when applied to active faults since the late Pleistocene, require knowing the average slip rate of the fault zone .

[0072] For the earthquake occurrence probability model of large earthquakes, since an earthquake can be regarded as the result of the accumulation of strain energy over time at a certain rate, in the case of in-situ recurrence, the possibility of earthquake recurrence is related to the time elapsed since the last earthquake in the local area, i.e., the waiting time. If the earthquake has not occurred after time, then on the condition of this, within the time period from to +Δt, the possibility of earthquake recurrence is expressed by the conditional probability:

[0073] where is the recurrence interval probability density function, is the cumulative probability distribution function, is the recurrence interval, is the waiting time, is the prediction time period.

[0074] Currently, the probability models available for seismic hazard analysis mainly include: Poisson distribution, Lognormal distribution, and BPT model (Brownian Passage Time model).

[0075] The Poisson model is based on the following assumptions: On a fault zone, earthquakes occur randomly in time and space, and the number of earthquakes and magnitudes conform to the Gutenberg-Richter relationship, that is, an exponential relationship. Its main feature is that it is considered that the probability of future earthquakes is independent of the elapsed time since the last earthquake. This model is more suitable when little is known about the laws and genetic mechanisms of earthquake gestation and occurrence. Moreover, since it requires fewer constraint parameters, even now, in areas lacking geological and seismic data, the Poisson model still plays an important role. The probability density function and conditional probability of the Poisson model are respectively:

[0076] Among them, is the average annual occurrence rate of earthquakes in the fault segment, .

[0077] The probability density function of the lognormal model is:

[0078] In the formula, is the earthquake recurrence interval, is the elapsed time; is the average earthquake recurrence interval; is the mean value, is the standard deviation (uncertainty), which includes aleatory uncertainty and epistemic uncertainty.

[0079] The BPT model is a strong earthquake recurrence and renewal model with an inherent physical basis proposed based on the elastic rebound theory. According to the elastic rebound theory, strong earthquakes occur when the stress accumulation on an active fault reaches a fixed upper limit, and then the stress of the fault drops to a fixed extremely low level and starts the next cycle. With the in-depth research and actual earthquake case observations, it is found that the upper and lower limits of stress are not fixed values but fluctuate (this fluctuation can be represented by the coefficient of variation), that is, the tectonic loading process will be interfered by some random events, showing a random loading process of stable loading with additional Brownian perturbations, and the recurrence intervals between earthquake events follow the Brownian process time distribution. Its probability density function is as follows: In the formula, is the probability density function of the BPT model; is the average recurrence interval of earthquakes; is the coefficient of variation, also known as the aperiodic factor, which is equal to the ratio of the standard deviation to the average recurrence interval of earthquakes.

[0080] The Poisson model assumes that the occurrence probability of earthquakes remains constant; these two results of the BPT model and the Lognormal model imply two different interpretations of the internal tectonic movement: the Lognormal model believes that the fault has become an inactive fault; while the BPT model believes that the fault itself is still accumulating or receiving strain energy transferred from adjacent faults, but its own stress state remains stable, and the strain energy it accumulates or receives is released through other means (such as creep or small earthquakes, etc.).

[0081] In another embodiment, as Figure 4 shown, the present invention provides a seismic hazard assessment system for moderately strong earthquake regions, including: Zoning tectonic module: used to perform zoning tectonics on the earthquake region to obtain multiple tectonic regions; Fitting calculation module: used to fit the historical earthquake and modern small and medium earthquake data in each tectonic region to obtain the magnitude-frequency relationship curve, and calculate the occurrence rate, occurrence probability, and recurrence interval of any magnitude earthquake in each tectonic region; Equal weight distribution module: using the spatial smoothing method to distribute the equal weights of each magnitude bin, the occurrence rate, occurrence probability, and recurrence interval of any magnitude earthquake in each tectonic region to each fault zone.

[0082] Further, using the spatial smoothing method to distribute the equal weights of each magnitude bin, the occurrence rate, occurrence probability, and recurrence interval of any magnitude earthquake in each tectonic region to each fault zone includes: Statistically analyze the historical destructive earthquake catalog and regional network earthquake catalog of the tectonic region, determine the magnitude bins to be distributed in each tectonic region, calculate the annual occurrence rate of earthquakes at all levels in the tectonic region according to the magnitude-frequency relationship formula, divide the tectonic region into uniform grids, calculate the seismic activity of each grid as the weight, use the moving average method to calculate the average value of the seismic activity in adjacent grids to smooth the data, and then, based on the weight and without exceeding the maximum potential magnitude, distribute the statistically obtained equal weights of each magnitude bin, the occurrence rate, occurrence probability, and recurrence interval of any magnitude earthquake in each tectonic region to each fault zone.

[0083] Further, dividing the tectonic region into uniform grids includes: dividing the tectonic region into grids with a size of 0.1°×0.1° in the longitude and latitude directions.

[0084] Further, the magnitude-frequency relationship formula is as follows: Among them, is the annual incidence rate of earthquakes of magnitude is the magnitude, is the seismic activity constant, and is the relative proportion coefficient.

[0085] Furthermore, the calculation formula for seismic activity degree is as follows:

[0086] Among them, is the seismic activity degree / seismic radiation energy, is the comprehensive magnitude of the tectonic area.

[0087] Furthermore, the method also includes: determining the maximum potential magnitude of each tectonic area according to the historical seismic activity, current seismic activity and the nature of the faults in the tectonic area; including the maximum potential magnitude of the fault zone in the tectonic area with the activity age of early to middle Pleistocene, the maximum potential magnitude of the fault zone in the tectonic area with the activity age of late Pleistocene, and the maximum potential magnitude of the fault zone in the tectonic area with the activity age before Quaternary.

[0088] Furthermore, the determination principle of the maximum potential magnitude of the fault zone in the tectonic area with the activity age of early to middle Pleistocene is as follows: If there is a fault intersection in the fault zone in the tectonic area, the activity nature of the fault is a strike-slip fault, the deep background of the fault is the edge of the depression and uplift, and the maximum historical earthquake magnitude is greater than or equal to 6, the maximum current small earthquake magnitude is greater than or equal to 4, and the length of the fault zone is greater than or equal to 30 km, then the maximum potential magnitude of the fault zone in the tectonic area with the activity age of early Pleistocene and the maximum potential magnitude of the fault zone in the tectonic area with the activity age of middle Pleistocene are 6.5; If the fault zone in the tectonic area belongs to non-fault intersection, the activity nature of the fault is a normal or reverse fault, the deep background of the fault is not the edge of the depression and uplift, and the maximum historical earthquake magnitude is greater than or equal to 5, the maximum current small earthquake magnitude is greater than or equal to 3, and the length of the fault zone is less than 30 km, then the maximum potential magnitude of the fault zone in the tectonic area with the activity age of early Pleistocene and the maximum potential magnitude of the fault zone in the tectonic area with the activity age of middle Pleistocene are 6.0.

[0089] Furthermore, the determination principle of the maximum potential magnitude of the fault zone in the tectonic area with the activity age of late Pleistocene is as follows: The maximum potential magnitude of the fault zone in the tectonic area with the activity age of late Pleistocene is calculated and determined through the regression relation formula.

[0090] Furthermore, the determination principle of the maximum potential magnitude of the fault zone in the tectonic area with the activity age before Quaternary is as follows: It is determined according to the background magnitude of the seismic zone.

[0091] Furthermore, it should be understood that since the settings of the respective modules are only for illustrating the functional units of the system of the present disclosure, the physical devices corresponding to these modules can be the processor itself, or a part of the software in the processor, a part of the hardware, or a part of the combination of software and hardware. Therefore, the number of each module in the figure is only illustrative.

[0092] The various embodiments of the systems and techniques described above in this document can be implemented in digital electronic circuit systems, integrated circuit systems, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems on a chip (SOCs), complex programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments can include: implemented in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which can be a dedicated or general-purpose programmable processor, and can receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit the data and instructions to the storage system, the at least one input device, and the at least one output device.

[0093] To solve the above technical problems, an embodiment of the present invention further provides a computer device / electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, it implements the steps of a method for seismic hazard assessment in a strong earthquake area as described above.

[0094] As Figure 5 shown, the computer / electronic device includes a memory, a processor, and a network interface that are communicatively connected to each other through a system bus. It should be noted that only a computer device having components such as a memory, a processor, a network interface, and an operating system is shown in the figure, but it should be understood that it is not required to implement all the shown components, and more or fewer components can be alternatively implemented. Among them, those skilled in the art of the present technology can understand that a computer / electronic device here is a device that can automatically perform numerical calculations and / or information processing according to pre-set or stored instructions, and its hardware includes but is not limited to microprocessors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), embedded devices, etc.

[0095] The computer / electronic device can be a computing device such as a desktop computer, a notebook, a handheld computer, and a cloud server. The computer / electronic device can interact with the user through a keyboard, a mouse, a remote control, a touchpad, or a voice control device.

[0096] There can be one or more memories, and at least one type of readable storage medium is included. The readable storage medium includes flash memory, a hard disk, a multimedia card, a card-type memory (such as an SD or DX memory, etc.), a random access memory (RAM), a static random access memory (SRAM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a programmable read-only memory (PROM), a magnetic memory, a magnetic disk, an optical disk, etc. In some embodiments, the memory can be an internal storage unit of the computer device, such as the hard disk or memory of the computer device. In other embodiments, the memory can also be an external storage device of the computer device, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) card, a FlashCard, etc., equipped on the computer device. Of course, the memory can also include both the internal storage unit and the external storage device of the computer device. In this embodiment, the memory is generally used to store the operating system and various application software installed on the computer device, such as the program code of a method for seismic hazard assessment in moderately strong earthquake regions. In addition, the memory can also be used to temporarily store various data that have been output or will be output.

[0097] In some embodiments, the processor can be a central processing unit (CPU), a controller, a microcontroller, a microprocessor, or other data processing chips. The processor is generally used to control the overall operation of the computer device. In this embodiment, the processor is used to run the program code stored in the memory or process data, such as running the program code of a method for seismic hazard assessment in moderately strong earthquake regions.

[0098] The network interface can include a wireless network interface and / or a wired network interface, and this network interface is generally used to establish a communication connection between the computer device and other electronic devices.

[0099] The present invention also provides another implementation manner, that is, to provide a readable storage medium on which a computer program is stored, and when the computer program is executed by a processor, the steps of a method for seismic hazard assessment in moderately strong earthquake regions as described above are implemented.

[0100] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0101] It is not difficult for those skilled in the art to understand that the present invention includes any combination of the above-mentioned invention content and specific implementation parts of the specification and each part shown in the drawings. Due to space limitations and to make the specification concise, the various solutions formed by these combinations are not described one by one. Any modification, equivalent replacement, improvement, etc., made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0102] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, replacements, and variations to the above embodiments within the scope of the present invention without departing from the principle and purpose of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for assessing earthquake hazard in moderate to strong earthquake zones, characterized in that: include: The earthquake zone is divided into several structural zones by structural division; The magnitude-frequency relationship was obtained by fitting the historical earthquake and modern small and medium earthquake data in each tectonic zone, and the annual occurrence rate, probability of occurrence and recurrence interval of any magnitude earthquake in each tectonic zone were calculated. For each tectonic zone, the spatial smoothing method is used to allocate the weights of each magnitude level, the annual occurrence rate of any magnitude earthquake in each tectonic zone, the probability of earthquake occurrence and the recurrence interval to each fault zone.

2. A method for assessing earthquake risk in a moderate to strong earthquake zone according to claim 1, characterized in that: The method of using the spatial smoothing method to distribute the weights of each magnitude level, the annual occurrence rate of any magnitude earthquake in each structural zone, the probability of earthquake occurrence and the recurrence interval to each fault zone includes: The historical destructive earthquake catalogs and regional network earthquake catalogs in the tectonic zone are statistically analyzed to determine the magnitude grades that need to be allocated to each tectonic zone. The annual incidence rates of earthquakes at all levels in the tectonic zone are calculated based on the magnitude-frequency relationship. The tectonic zone is divided into uniform grids, and the seismic activity of each grid is calculated as a weight. The moving average method is used to calculate the average value of seismic activity in similar grids to smooth the data. Based on the weights, the statistically obtained weights of each magnitude grade, the annual incidence rate of earthquakes of any level in each tectonic zone, the probability of earthquake occurrence and the recurrence interval are allocated to each fault zone without exceeding the maximum potential magnitude.

3. A method for assessing earthquake risk in a moderate to strong earthquake zone according to claim 2, characterized in that: The dividing the structural area into uniform grids includes: dividing the structural area into grids of 0.1°×0.1° in the longitude and latitude directions.

4. A method for assessing earthquake risk in a moderate to strong earthquake zone according to claim 2, characterized in that: The magnitude-frequency relationship is as follows: in, for The annual occurrence rate of earthquakes is the magnitude, is the seismic activity constant, Relative scale factor.

5. A method for assessing earthquake risk in a moderate to strong earthquake zone according to claim 2, characterized in that: The calculation formula of seismic activity is as follows: in, is the seismic activity, For magnitude.

6. A method for assessing earthquake risk in a moderate to strong earthquake zone according to claim 2, characterized in that: Also includes: The maximum potential magnitude of each tectonic zone is determined based on the historical seismic activity, current seismic activity and the nature of the faults in the tectonic zone, including the maximum potential magnitude when the fault zones in the tectonic zone were active in the Early and Middle Pleistocene, the maximum potential magnitude when the fault zones in the tectonic zone were active in the Late Pleistocene, and the maximum potential magnitude when the fault zones in the tectonic zone were active before the Quaternary.

7. A method for assessing earthquake risk in a moderate to strong earthquake zone according to claim 5, characterized in that: The principles for determining the maximum potential magnitude of the fault zone in the tectonic area in the early and middle Pleistocene are as follows: If there is a fault intersection in the fault zone in the tectonic zone, the active nature of the fault is a strike-slip fault, the deep background of the fault is the edge of a depression and uplift, and the maximum magnitude of the historical earthquake is greater than or equal to 6, the maximum magnitude of the current small earthquake is greater than or equal to 4, and the length of the fault zone is greater than or equal to 30 kilometers, then the maximum potential magnitude of the fault zone in the tectonic zone is 6.5 when the active age of the fault zone is the Early Pleistocene, and the maximum potential magnitude of the fault zone in the tectonic zone is 6.5 when the active age of the fault zone is the Middle Pleistocene; If the fault zone in the tectonic area is a non-fault intersection, the active nature of the fault is a normal fault or a reverse fault, the deep background of the fault is the edge of a non-depression uplift, and the maximum magnitude of the historical earthquake is greater than or equal to 5, the maximum magnitude of the current small earthquake is greater than or equal to 3, and the length of the fault zone is less than 30 kilometers, then the maximum potential magnitude of the fault zone in the tectonic area is 6.0 when the activity era of the fault zone is the Early Pleistocene, and the maximum potential magnitude of the fault zone in the tectonic area is 6.0 when the activity era of the fault zone is the Middle Pleistocene.

8. A method for assessing earthquake risk in a moderate to strong earthquake zone according to claim 5, characterized in that: The principle for determining the maximum potential magnitude of an earthquake in which the fault zone in the tectonic area is active in the late Pleistocene is as follows: The maximum potential magnitude of an earthquake in which the fault zone in the tectonic area is active in the late Pleistocene is determined by calculating the regression relationship.

9. A method for assessing earthquake risk in a moderate to strong earthquake zone according to claim 5, characterized in that: The principle for determining the maximum potential magnitude of the fault zone in the tectonic area before the Quaternary period is as follows: it is determined according to the background magnitude of the seismic zone.

10. A seismic risk assessment system for moderate to strong earthquake areas, characterized in that: include: Partition construction module: used to partition the earthquake zone to obtain multiple structural zones; Fitting calculation module: used to fit the historical earthquake and modern small and medium earthquake data in each tectonic zone to obtain the magnitude-frequency relationship curve, and calculate the occurrence rate, probability of occurrence and recurrence interval of any magnitude earthquake in each tectonic zone; Equal weight distribution module: For each tectonic zone, the spatial smoothing method is used to distribute the weights of each magnitude level, the occurrence rate of any magnitude earthquake in each tectonic zone, the probability of earthquake occurrence and the recurrence interval to each fault zone.

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