A stratum structure scanning method based on a single-station six-component seismograph

Abstract

The application discloses a stratum structure scanning method based on a single-station six-component seismograph, and steps of the method comprise the following steps: S1: selecting one or more measuring points in a target area; installing a single-station six-component seismograph to each measuring point to collect passive source signals; S2: calculating horizontal components of translation and rotation according to six-component data of passive source signals of the measuring points; S3: extracting phase velocity dispersion curves at the measuring points according to component data characteristics in the six-component data of passive source signals of the measuring points and relationship characteristics among the component data, and obtaining quantitative relationships between phase velocities and frequencies; S4: calculating relative velocities at different frequency points of the corresponding measuring points according to the phase velocity dispersion curves and the quantitative relationships; S5: establishing a mapping relationship between the relative velocities and depths according to the quantitative relationships, and obtaining underground structures of the corresponding measuring points; and S6: completing stratum profile information drawing or underground three-dimensional structure inversion of the target area according to the underground structures of the measuring points in the target area.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of stratum structure inversion, and particularly relates to a stratum structure scanning method based on a single-station six-component seismograph. BACKGROUND

[0002] Stratum structure inversion technology is a key technology widely used in the field of geological exploration. It can analyze the propagation characteristics of seismic waves in underground media based on data observed on the ground or downhole, and infer the distribution, physical properties and geometric structure of underground structures. This technology not only helps to study seismic activity and crustal movement, understand the internal structure of the Earth, but also assists in finding underground water, mineral resources and oil and gas reservoirs. In addition, it also has important applications in monitoring geological disasters such as landslides, collapses, etc.

[0003] The current application range of stratum structure inversion technology is very wide. The most common method at present is to use the reflection, refraction and scattering of seismic waves in underground media. Through detailed analysis of these seismic waves, information such as velocity structure, density distribution and elastic parameters of underground media can be inferred. Among them, the velocity structure is the most critical parameter in the inversion process, because it is directly related to the propagation velocity of seismic waves, thereby affecting the recording of seismic waveforms.

[0004] There are many methods for stratum structure inversion, including arrival time inversion, waveform inversion, full waveform inversion, etc. Arrival time inversion mainly uses the travel time of seismic waves from the source to the receiver to infer the underground velocity structure. Waveform inversion pays more attention to the details of seismic waveforms. It matches the actual observed seismic waveforms with the theoretically calculated seismic waveforms to invert the physical parameters of the underground medium. Full waveform inversion is one of the more advanced methods. It not only considers the arrival time of seismic waves, but also considers the amplitude, frequency and phase information of seismic waves, thereby providing more accurate underground structure information.

[0005] In order to realize stratum structure inversion, a large number of seismograph station arrays need to be laid out. These stations can be ground stations, submarine stations or downhole stations. The number and distribution of stations have a direct impact on the accuracy of the inversion results. Generally speaking, the more stations, the wider the coverage, the more detailed the underground structure information obtained by inversion. However, the layout of stations is also limited by geographical environment and economic cost, so in actual operation, a balance needs to be found between the number of stations and the accuracy of inversion.

[0006] In addition, due to the deployment of a large number of seismic station, the corresponding data volume also grows rapidly, which often means higher computing power requirements and longer processing time in the later computer processing. Considering the high cost required by deploying a large number of station arrays, and the different degrees of limitations of the experimental site, there are certain limitations and deficiencies in practical application. SUMMARY

[0007] In view of the fact that the conventional stratum structure inversion method does not sufficiently utilize the characteristics of each component of the signal and the relationship between each component, at least two or more seismic stations are required for positioning in theory and practical application, the present application provides a stratum structure inversion method in the vertical direction of the measuring point, which fully utilizes the relationship between each component of the six-component data. The present application effectively utilizes the relationship between each component of the collected signal, and makes a more in-depth analysis of the information carried by the data, so that the inversion of the underground structure of the corresponding measuring point can be realized by using a single seismic station. Under the premise of using a single station six-component seismometer, the underground structure information obtained by jointly giving multiple measuring points on the measuring line can obtain the corresponding stratum structure profile information under the measuring line. By combining the information of multiple measuring lines, the underground three-dimensional structure information can be further obtained.

[0008] The stratum structure inversion method of the present application only uses a single station six-component seismometer, compared with the inversion method based on the sensor array, the present application only needs a single station six-component seismometer to measure each measuring point in time sequence, so that the stratum structure profile information on the corresponding measuring line can be obtained, or the underground three-dimensional structure information can be obtained by integrating the data results of multiple measuring lines, and the stratum structure scanning effect can be realized. Moreover, the present application only uses single station data, and the speed of later processing is faster, and the algorithm complexity is significantly reduced. The traditional method needs to arrange a large number of sensors to form an array at a single measuring point to realize data acquisition of a single measuring point, and the array method requires that the sound source must be uniform (such as a passive seismic source at the same time), and the present method does not have this requirement.

[0009] The technical scheme adopted by the present application to solve the technical problems is:

[0010] The traditional instrument deployment method for stratum structure inversion in the stratum structure inversion technology is as follows: Figure 1As shown, the present application improves the method by using a single station six-component seismograph to collect data at each measuring point in time, thereby realizing the stratum structure inversion of the single station six-component seismograph. The technical scheme is mainly based on the fact that the seismic waves generated by reasons such as rock rupture contain body waves and surface waves, and are affected by the stratum structure at different depths during propagation. When different types of waves reach the measuring point, interference occurs, and the stratum information at different depths is reflected on the six-component data at the measuring point, so that the stratum structure inversion can be realized. Since earthquakes, plate movement, volcanic activity, or human underground blasting and mineral excavation will generate certain seismic waves, and different seismic wave mixtures can be used as passive source signals as a whole, the technical scheme can also be applied to the field of mineral exploitation.

[0011] The flowchart of the stratum structure inversion technology based on the single station six-component seismograph is as shown in the figure. Figure 2 Before installation, remove the surface soil, and tightly couple a single station on the ground to effectively collect and process passive source signals, which specifically includes the following steps:

[0012] S1: Align the six components of the six-component seismograph with the corresponding reality, ensure that the z component of the six-component seismograph points in the direction opposite to the gravitational acceleration at the measuring point during installation, and tightly couple a single seismograph on the ground to collect passive source signals at a fixed sampling rate. After a certain time sampling, save the data;

[0013] S2: Preprocess the collected signals, align the data steps, remove singular points and obvious human factors in the measurement experiment, remove data trends, obtain the passive source signal six-component data of the measuring point, and further calculate the horizontal components of translation and rotation according to the six-component data, while saving the position information of the measuring point;

[0014] S3: Comprehensive analysis of the characteristics of each component data after preprocessing and the relationship characteristics between the component data, extract the phase velocity dispersion curve at the measuring point, and obtain the quantitative relationship between phase velocity and frequency;

[0015] S4: On the basis of obtaining the phase velocity dispersion curve, according to the quantitative relationship between phase velocity and frequency, calculate the relative velocity at different frequency points, and save the relative velocity and the corresponding frequency point information;

[0016] S5: Using the basic principle of interference at a single point on the ground during seismic wave propagation, combining the quantitative relationship between the foregoing relative velocity and frequency, and further establishing the mapping relationship between the relative velocity and the depth, obtaining the structure information of the stratum at different depths at the measuring point, and completing the underground structure detection of a single measuring point;

[0017] S6: On the basis of single-point underground structure detection, the measuring points are combined into measuring lines or measuring point arrays through reasonable planning, and the aforementioned steps are repeated at each point, so that stratum profile information drawing or underground three-dimensional structure inversion can be realized.

[0018] Preferably, in step S1, the six components of the six-component seismograph are aligned with the corresponding directions in reality, including the three components of translation and rotation, i.e., the x component, the y component, and the z component, which are directed to the north-south direction, the east-west direction, and the up-down direction, respectively, wherein the positive direction of the z component is directed to the direction opposite to the gravitational acceleration.

[0019] Preferably, in step S3, the phase velocity dispersion curve at the measuring point is extracted by analyzing the characteristics of each component data and the relationship between the component data after preprocessing, mainly by utilizing the relationship characteristics between the six-component data caused by single-point interference of different types of waves of the same passive source signal at the measuring point during propagation, so that the data of each component in the same time window needs to be used.

[0020] Preferably, the passive source signals between different measuring points in step S6 do not require time synchronization, so that the data can be collected by the single-station six-component seismograph at each measuring point or by multiple instruments simultaneously. When multiple instruments are used for simultaneous deployment, the experimental duration can be shortened without increasing the algorithm complexity, and additional computing power is not required for data processing in the later stage. At the same time, when multiple instruments are used for simultaneous deployment, the method of sensor array is also combined to verify the results of stratum structure inversion from two aspects.

[0021] The present application utilizes the relationship characteristics between the six-component data caused by single-point interference of different types of waves of the same passive source signal at the measuring point during propagation, and the phase velocity dispersion curve at the measuring point can be extracted by using the six-component data of a single station and the relationship characteristics between the component data, so that the stratum profile information inversion or underground three-dimensional structure inversion can be realized by using signals collected by a single station.

[0022] Compared with the prior art, the positive effects of the present application are as follows:

[0023] The stratum structure scanning technology based on a single-station six-component seismograph proposed in the present application only needs a single-station six-component seismograph in the actual application process, which significantly reduces the requirements for instrument deployment and experimental environment in the experiment compared with the multi-station array method, and the data processing method proposed is significantly faster than the common station array inversion method. In addition, compared with the active source method, the present application uses a passive source as a signal source, which effectively increases flexibility and can realize stratum structure scanning at a lower cost. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is an example diagram of a conventional instrument deployment method for stratum structure inversion based on time-of-flight and the like.

[0025] Figure 2 is the flow chart of stratum structure inversion technology based on single station six-component seismograph of the present application.

[0026] Figure 3 is the specific implementation effect diagram of stratum profile structure inversion of a certain domestic Sichuan survey line. DETAILED DESCRIPTION

[0027] The flow chart of stratum structure inversion technology based on single station six-component seismograph is shown in Figure 2 The single station is tightly coupled on the ground to collect passive source signals and process them, which specifically includes the following steps:

[0028] S1: For each survey point selected in the target area, the three components x component, y component and z component of the six-component seismograph are aligned with the north-south direction, east-west direction and up-down direction respectively, and in the installation process, the positive direction of the z component is ensured to point to the direction opposite to the gravitational acceleration at the survey point. The single seismograph tightly coupled on the ground collects passive source signals at the survey point at a fixed sampling rate, saves the data after a certain time sampling, and is recorded as a x (t), a y (t), a z (t), r x (t), r y (t), r z (t), where a x (t), a y (t) is the horizontal component of passive source translational data, a z (t) is the vertical component of passive source translational data, r x (t), r y (t) is the horizontal component of passive source rotational data, r z (t) is the vertical component of passive source rotational data;

[0029] S2: The signals collected at the i-th survey point are preprocessed, the data steps are aligned, the singular points and obvious artificial factors in the measurement experiment are removed, the data trend is removed, and the six-component data of passive source signals at the survey point a′ x (t), a′ y (t), a′ z (t), r′ x (t), r′ y (t), r′ z (t) are obtained, and further, the horizontal components a′ T (t) and r′ T (t) of translation and rotation are calculated according to the six-component data, and the position information s of the survey point is saved.i ;

[0030] S3: Comprehensive analysis of the preprocessed six-component data a′ x (t), a′ y (t),a′ z (t),r′ x (t), r′ y (t),r′ z Based on the characteristics of (t) and the relationship between the data of each component, the phase velocity dispersion curve v(f) at the measuring point is extracted to obtain the quantitative relationship between phase velocity v and frequency f.

[0031] S4: Based on the obtained phase velocity dispersion curve v(f), calculate the relative velocity v'(f0) at different frequency points f0 according to the quantitative relationship between phase velocity v and frequency f, and save the relative velocity v'(f0) and the corresponding frequency point f0 information;

[0032] S5: Utilizing the basic principle of interference occurring at a single point on the ground during the propagation of seismic waves, and combining the aforementioned quantitative relationship between relative velocity v' and frequency f, a mapping relationship v'(d) between relative velocity v' and depth d is established to obtain structural information of the strata at different depths at the measuring point, thus completing the underground structure detection of a single measuring point;

[0033] S6: Based on the underground structure detection of a single measuring point, a measuring line s is formed by rationally planning the combination of measuring points. i ,i=1,2,3…N, where N is the total number of measuring points; or the measuring points can be combined into a measuring point array (s p ,s q ), where p = 1, 2, 3…, P, q = 1, 2, 3… Q, P is the total number of measuring points in each row of the measuring point array, and Q is the total number of measuring points in each column of the measuring point array; repeating steps S1 to S5 at each side point location can realize the drawing of stratigraphic profile information v'(s i ,d) or underground three-dimensional structure inversion v'(s p ,s q ,d).

[0034] Preferably, the outlier removal methods used in step S2 include, but are not limited to, Grubbs' criterion, outlier detection, normalization, clustering, and the 3-σ principle. Taking the 3-σ principle as an example, the specific formula for outlier detection in sequence a(n) is as follows:

[0035]

[0036] Where a mean Let a(n) be the average value, a var Let a(n) be the variance, a ′(n) is a replacement value of the singular value, and the replacement value is obtained by using a method selected from the group consisting of mean imputation, median imputation, mode imputation, Lagrange interpolation, random forest, and the like.

[0037] Preferably, the horizontal components a′ T (t) and r′ T The specific formula of a′

[0038] a ′ T (t) = a ′ x (t) sin θ + a ′ y (t) cos θ

[0039] r ′ T (t) = r ′ x (t) sin θ + r ′ y (t) cos θ

[0040] where θ is the back azimuth of the incoming wave, and the back azimuth θ of the incoming wave is obtained by using a method selected from the group consisting of measurement, correlation, filtering, and the like.

[0041] Preferably, the method for extracting the phase velocity dispersion curve v(f) at the measuring point in step S3 is based on the principle that different types of waves of the same passive source signal will interfere at the measuring point during propagation. The phase velocity dispersion curve v(f) at the measuring point is obtained by analyzing the relationship between a′ x (t), a′ y (t), a′ z (t), r′ x (t), r′ y (t), r′ z (t). The method for obtaining the phase velocity dispersion curve v(f) includes, but is not limited to, the methods of damped least squares, genetic algorithm, Bayesian algorithm, and single-point interference, etc. Taking the single-point interference method as an example, the calculation formula of the dispersion curve v(f) is as follows:

[0042]

[0043] where α is the horizontal component, and r is the rotational component.

[0044] Preferably, the method for calculating the relative velocity v′(f) at different frequency points according to the quantitative relationship v(f) between the phase velocity v and the frequency f in step S4 is an improved method for different scale environments, and the specific implementation method is as follows:

[0045]

[0046] wherein wherein v(f k ) is the phase velocity of the kth frequency f k , and the fourth power of v 4 (f k ) is v 4 (f k ), k = 1 ~ K, K is the total number of frequency points.

[0047] Preferably, the mapping relationship v'(d) between the relative velocity v' and the depth d in step S5 is obtained based on the half-wavelength theory or the skin effect according to the basic principle of interference at a single point on the ground surface in the seismic wave propagation process, and the mapping relationship v'(d) between the relative velocity v' and the depth d is achieved by inverting the stratum structure at a single measuring point. Taking the half-wavelength theory as an example, the depth d can be calculated from the frequency f:

[0048]

[0049] wherein c is the wave number, f is the frequency, and the depth d is exactly half of the wavelength λ, so it is called the half-wavelength theory.

[0050] Figure 3 The schematic diagram of the longitudinal section inversion result of the stratum structure in the range of 700 meters along the measuring line s i , i = 1, 2, 3…N is drawn, and the high-speed layer at a depth of 200 meters and the rock base below a depth of 800 meters can be clearly seen in the diagram.

[0051] The above has described the present application in detail, but apparently the specific implementation form of the present application is not limited to this. For those skilled in the art, various obvious changes made to it without departing from the spirit of the method described in the present application and the scope of the claims are within the protection scope of the present application.

Claims

1. A method for scanning stratum structure based on single-station six-component seismometer, comprising the steps of: S1: selecting one or more measuring points in a target area; installing a single-station six-component seismometer at each measuring point to collect passive source signals; or installing a single-station six-component seismometer at each measuring point to collect passive source signals simultaneously; S2: pre-processing the passive source signals collected from each measuring point to obtain six-component data of passive source signals corresponding to the measuring point, calculating the horizontal components of translation and rotation according to the six-component data of passive source signals, and saving the position information of the measuring point; S3: extracting the phase velocity dispersion curve at the measuring point according to the component data characteristics and the relationship characteristics between the component data in the six-component data of passive source signals corresponding to the measuring point, and obtaining the quantitative relationship between phase velocity and frequency; S4: calculating the phase velocity of the corresponding measuring point at different frequencies according to the phase velocity dispersion curve and the quantitative relationship; wherein, according to the formula The phase velocity v ′ (f k ) of the corresponding measuring point at different frequencies f k is calculated. k ′ k Wherein v(f k ) is the phase velocity of the kth frequency f k , k = 1 ~ K, K is the total number of frequencies; S5: establishing the mapping relationship between relative velocity and depth according to the quantitative relationship, and obtaining the underground structure of the corresponding measuring point; S6: completing the stratum profile information drawing or underground three-dimensional structure inversion of the target area according to the underground structures of the measuring points in the target area.

2. The method of claim 1, wherein, The passive source signal collected is denoted a x (t), a y (t), a z (t), r x (t), r y (t), r z (t); Among them, a x (t), a y (t) represents the horizontal component of the passive source translational data, a z (t) represents the vertical component of the passive source translational data, r x (t), r y (t) represents the horizontal component of the passive source rotation data, r z (t) represents the vertical component of the passive source rotation data; based on the preprocessed six-component data a′ of the passive source signal. x (t), a′ y (t), a′ z (t), r′ x (t), r′ y (t), r′ z (t) Calculate the horizontal component of the translation a′ T (t) and the horizontal component of rotation r′ T (t).

3. The method of claim 2, wherein, Horizontal component of translation a ′ T (t) = a ′ x (t) sin θ + a ′ y (t) cos θ, horizontal component of rotation r ′ T (t) = r ′ x (t) sin θ + r ′ y (t) cos θ; where θ is the back azimuth of the incoming wave.

4. The method of claim 2, wherein, The method for pre-processing the passive source signals comprises sequentially aligning the data steps, removing singular points and human factors in the measurement, and removing data trends. The method for removing singular points comprises Grubbs criterion, outlier detection, normalization, clustering, and 3-σ principle. The phase velocity dispersion curve v(f) at the measuring point is obtained by using the damped least squares method, genetic algorithm, Bayesian algorithm or single-point interference method.

5. The method according to claim 2 or 3, characterized in that, The mapping relationship v'(d) between relative velocity v' and depth d is obtained based on the half-wavelength theory or skin effect.

6. The method according to claim 1 or 2 or 3, characterized in that, The method for installing a single-station six-component seismometer at each measuring point comprises aligning the directions of the x, y and z components of translation and rotation of the single-station six-component seismometer with the north-south direction, east-west direction and up-down direction, respectively, and pointing the positive direction of the z component to the direction opposite to the gravitational acceleration at the measuring point.

7. The method of claim 1, wherein, The multiple measuring points selected in the target area form a measuring line or a measuring point array, and when collecting data for multiple measuring points, only the single-station six-component seismometer needs to be measured sequentially.

8. The method of claim 1, wherein, ​

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