Stratum structure scanning method based on single-station six-component seismograph

Abstract

The invention discloses a stratigraphic structure scanning method based on a single-station six-component seismograph. The stratigraphic structure scanning method comprises the following steps: S1, selecting one or more measuring points in a target area; a single-station six-component seismograph is installed at each measuring point to acquire a passive source signal; s2, calculating horizontal components of translation and rotation according to passive source signal six-component data of the measuring point; s3, according to component data characteristics in the six-component data of the passive source signal of the measuring point and relation characteristics among the component data, extracting a phase velocity frequency dispersion curve at the measuring point, and obtaining a quantitative relation between the phase velocity and the frequency; s4, according to the phase velocity frequency dispersion curve and the quantitative relation, calculating relative velocities at different frequency points of the corresponding measuring points; s5, establishing a mapping relation between the relative speed and the depth according to the quantitative relation, and obtaining an underground structure of the corresponding measuring point; and S6, according to the underground structure of each measuring point of the target area, completing stratigraphic profile information drawing or underground three-dimensional structure inversion of the target area.

Description

Technical Field

[0001] The invention belongs to the technical field of stratum structure inversion, and in particular relates to a stratum structure scanning method based on a six-component seismograph at a single station. Background Art

[0002] Stratigraphic 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 ground or underground observation data, and infer the distribution, physical properties and geometric structure of underground structures. This technology not only helps to study earthquake activity and crustal movement, understand the structure of the earth's interior, but also assists in finding groundwater, mineral resources and oil and gas reservoirs. In addition, it also has important applications in monitoring geological disasters such as landslides and collapses.

[0003] The current application scope of stratigraphic structure inversion technology is very wide. The most common method is to use the reflection, refraction and scattering of seismic waves in underground media. Through the detailed analysis of these seismic waves, the velocity structure, density distribution and elastic parameters of the underground medium 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 speed of seismic waves, thus affecting the recording of seismic waveforms.

[0004] There are many methods for stratigraphic structure inversion technology, including arrival time inversion, waveform inversion, full waveform inversion, etc. Arrival time inversion mainly uses the propagation time of seismic waves from the source to the receiving point to infer the underground velocity structure. Waveform inversion pays more attention to the details of the seismic waveform. It inverts the physical parameters of the underground medium by matching the actual observed seismic waveform with the theoretically calculated seismic waveform. Full waveform inversion is one of the more advanced methods. It not only considers the arrival time of the seismic wave, but also comprehensively considers the amplitude, frequency and phase of the seismic wave, so as to provide more accurate underground structure information.

[0005] In order to achieve stratigraphic structure inversion, a large number of seismic station arrays are usually required. These stations can be ground stations, seabed stations or underground stations. The number and distribution of stations have a direct impact on the accuracy of the inversion results. Generally speaking, the more stations there are and the wider the coverage, the more detailed the underground structure information obtained by inversion. However, the layout of stations is also limited by the geographical environment and economic costs. Therefore, in actual operation, it is necessary to find a balance between the number of stations and the inversion accuracy.

[0006] In addition, due to the deployment of a large number of seismograph stations, the amount of data has also increased rapidly, which often means higher computing power requirements and longer processing time in the later computer processing process. Considering the high cost of deploying a large number of station arrays and the fact that the experimental site often has varying degrees of restrictions, there are certain limitations and deficiencies in practical applications. Summary of the invention

[0007] In view of the fact that the traditional stratigraphic structure inversion method does not fully utilize the characteristics of each signal component and the relationship characteristics between each component, and at least two seismic stations are required for positioning both in theory and in practical applications, the present invention provides a stratigraphic structure inversion method in the vertical direction of the measuring point by fully utilizing the relationship characteristics between each component of the six-component data. The present invention effectively utilizes the relationship between each component of the collected signal, conducts a more in-depth analysis of the information carried by the data, and can realize the inversion of the underground structure of the corresponding measuring point using a single seismic station. Under the premise of using a single-station six-component seismograph, by combining the underground structure information obtained from multiple measuring points on a given survey line, the corresponding stratigraphic structure profile information under the survey line can be obtained. By combining the information of multiple survey lines, the underground three-dimensional structure information can be obtained.

[0008] The stratigraphic structure inversion method of the present invention only uses a single-station six-component seismograph. Compared with the inversion method based on the sensor array, the present invention only needs a single-station six-component seismograph to measure each measuring point in time sequence, so as to obtain stratigraphic structure profile information on the corresponding survey line, or obtain underground three-dimensional structure information by integrating the data results of multiple survey lines, so as to achieve the stratigraphic structure scanning effect. In addition, the present invention only uses data from a single station, which is faster when performing post-processing, and the algorithm complexity is significantly reduced. The traditional method requires a large number of sensors to be arranged at a single measuring point to form an array to realize data collection at a single measuring point. The array method requires that the sound source must be unified (such as the active source at the same time), and the present method does not have this requirement.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] In the traditional method of stratum structure inversion, the instrument deployment method based on the arrival time and other methods is as follows: Figure 1As shown, the present invention improves the method by using a single-station six-component seismograph to collect data at each measuring point in time sequence, thereby realizing the inversion of the stratigraphic structure of the single-station six-component seismograph. The technical solution is mainly based on the fact that seismic waves generated by reasons such as rock fracture contain both body waves and surface waves, which will be affected by stratigraphic structures of different depths during propagation. When different types of waves reach the measuring point, interference occurs, and stratigraphic information of different depths is reflected in the six-component data at the measuring point, thereby realizing the inversion of the stratigraphic structure. Since earthquakes, plate movements, volcanic activities, or artificial underground blasting and mineral excavation will generate certain seismic waves, and different seismic wave hybrids can be used as passive source signals as a whole, the technical solution can also be applied to fields such as mineral mining.

[0011] The flow chart of the stratum structure inversion technology based on the six-component seismograph at a single station of the present invention is as follows: Figure 2 As shown in the figure, the surface soil is removed before installation, and a single station is tightly coupled to the ground to effectively collect passive source signals and process them. The specific steps include:

[0012] S1: Align the six components of the six-component seismograph with the corresponding ones in reality. During the installation process, ensure that the positive direction of the z component of the six-component seismograph points to the direction opposite to the gravity acceleration at the measuring point. The single seismograph tightly coupled to the ground collects passive source signals at a fixed sampling rate, and saves the data after a certain period of sampling.

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

[0014] S3: Comprehensively analyze 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 the phase velocity and the frequency, the relative velocity at different frequency points is calculated, and the relative velocity and the corresponding frequency point information are saved;

[0016] S5: Using the basic principle of interference at a single point on the ground during the propagation of seismic waves, combined with the aforementioned quantitative relationship between relative velocity and frequency, a mapping relationship between relative velocity and depth is established to obtain structural information at different depths of the formation at the measuring point, thus completing the underground structure detection at a single measuring point;

[0017] S6: Based on the underground structure detection of a single measuring point, by rationally planning the measuring points into a measuring line or a measuring point array and repeating the above steps at each point, stratigraphic profile information drawing or underground three-dimensional structure inversion can be achieved.

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

[0019] Preferably, in step S3, the characteristics of each component data after preprocessing and the relationship characteristics between the component data are comprehensively analyzed to extract the phase velocity dispersion curve at the measuring point, mainly using the relationship characteristics between the six component data caused by single-point interference at the measuring point during the propagation of different types of waves of the same passive source signal. Therefore, it is necessary to use the data of each component in the same time window.

[0020] Preferably, the passive source signals between different measuring points in step S6 do not require time synchronization, so a single station six-component seismograph can collect data point by point, or multiple instruments can be used to collect data simultaneously. When multiple instruments are deployed simultaneously, the experimental time can be shortened without increasing the complexity of the algorithm, and no additional computing power is required for later data processing. At the same time, when multiple instruments are deployed simultaneously, the sensor array method is also combined to verify the results of the stratigraphic structure inversion from two aspects.

[0021] The present invention utilizes the relationship characteristics between six-component data caused by single-point interference at the measuring point during the propagation of different types of waves of the same passive source signal. The six-component data of a single station and the relationship characteristics between the component data can be used to extract the phase velocity dispersion curve at the measuring point. Only a single station is used to collect signals to achieve inversion of stratigraphic profile information or underground three-dimensional structure inversion.

[0022] Compared with the prior art, the present invention has the following positive effects:

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

[0024] Figure 1 This is an example diagram of the instrument deployment method for traditional stratigraphic structure inversion based on methods such as arrival time.

[0025] Figure 2 It is a flow chart of the stratum structure inversion technology based on a six-component seismograph at a single station proposed by the present invention.

[0026] Figure 3 It is a specific implementation effect diagram of the present invention applied to the inversion of stratigraphic profile structure under a geological survey line in Sichuan, China. DETAILED DESCRIPTION

[0027] The flow chart of the stratigraphic structure inversion technology based on a six-component seismometer at a single station is as follows: Figure 2 As shown, a 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 measuring point selected in the target area, the three components of the six-component seismograph's translation and rotation, the x component, the y component, and the z component, are aligned with the north-south, east-west, and up-down directions respectively. During the installation process, ensure that the positive direction of the z component points to the direction opposite to the gravity acceleration at the measuring point. A single seismograph tightly coupled to the ground collects the passive source signal at the measuring point at a fixed sampling rate. After a certain period of sampling, the data is saved and 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 the passive source translation data, a z (t) is the vertical component of the passive source translation data, r x (t), r y (t) is the horizontal component of the passive source rotation data, r z (t) is the vertical component of the passive source rotation data;

[0029] S2: Preprocess the signal collected at the i-th measuring point, align the data time step, remove the singular value points and obvious human factors in the measurement experiment, remove the data trend, and obtain the six-component data a′ of the passive source signal at the measuring point x (t), a′ y (t),a′ z (t),r′ x (t), r′ y (t),r′ z (t), and further calculate the horizontal component a′ of translation and rotation based on the six-component data T (t) and r′ T (t), and save the position information s of the measuring pointi ;

[0030] S3: Comprehensive analysis of the six-component data a′ after preprocessing x (t), a′ y (t),a′ z (t),r′ x (t), r′ y (t),r′ z (t) and the relationship characteristics between the component data, extract the phase velocity dispersion curve v(f) at the measuring point, and obtain the quantitative relationship between the phase velocity v and the frequency f;

[0031] S4: On the basis of obtaining the phase velocity dispersion curve v(f), according to the quantitative relationship between the phase velocity v and the frequency f, the relative velocity v'(f0) at different frequency points f0 is calculated, and the relative velocity v'(f0) and the corresponding frequency point f0 information are saved;

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

[0033] S6: Based on the underground structure detection of a single measuring point, the measuring points are combined into a measuring line through reasonable planning i , i = 1, 2, 3 ... N, N is the total number of measuring points; or the measuring points are combined into a measuring point matrix (s p ,s q ), where p = 1, 2, 3 ..., P, q = 1, 2, 3 ... Q, P is the total number of points in each row of the measuring point matrix, and Q is the total number of points in each column of the measuring point matrix; repeating steps S1 to S5 at each side point position 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 method for removing singular value points in step S2 includes but is not limited to methods such as Grubbs criterion, outlier detection, normalization, clustering, 3-σ principle, etc. Taking the 3-σ principle as an example, the specific formula for detecting outliers in the sequence a(n) is:

[0035]

[0036] where a mean is the average value of a(n), a var is the variance of a(n), a ′(n) is a replacement value for a singular value, and methods for obtaining the replacement value include but are not limited to mean interpolation, median interpolation, majority interpolation, Lagrange interpolation, random forest method, etc.

[0037] Preferably, in step S2, the horizontal component a′ of the translation and rotation is calculated according to the six-component data. T (t) and r′ T The specific formula for (t) is:

[0038] a ′ T (t) = a ′ x (t)sinθ+a ′ y (t)cosθ

[0039] r ′ T (t) = r ′ x (t)sinθ+r ′ y (t)cosθ

[0040] Wherein θ is the rear azimuth angle of the incoming wave. Methods for calculating the rear azimuth angle θ of the incoming wave include but are not limited to actual measurement method, correlation method, filtering method, etc.

[0041] Preferably, the method for extracting the phase velocity dispersion curve v(f) at the measuring point in step S3 is to use the principle that different types of waves of the same passive source signal will cause single-point interference at the measuring point during propagation, and to analyze the six-component data a′ x (t), a′ y (t),a′ z (t),r′ x (t), r′ y (t),r′ z (t) is used to obtain the surface wave phase velocity dispersion curve v(f) at the measuring point. The methods for obtaining the surface wave phase velocity dispersion curve include but are not limited to the damped least squares method, genetic algorithm, Bayesian algorithm and single-point interferometry. Taking the single-point interferometry as an example, the calculation formula of the dispersion curve v(f) is:

[0042]

[0043] Where α is the translational component and r is the rotational component.

[0044] Preferably, in step S4, 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 is an improved step for different scale environments, and the specific implementation method is:

[0045]

[0046] in Where v(f k ) is the kth frequency point f k The phase velocity, to the fourth power, 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 is established in step S5 based on the basic principle that interference occurs at a single point on the ground during the propagation of seismic waves. The mapping relationship v'(d) between the relative velocity v' and the depth d is obtained based on the half-wavelength theory or the skin effect to achieve the inversion of the stratigraphic 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] Where 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 700-meter range is mapped on the survey line s i , i=1,2,3…N is a schematic diagram of the longitudinal section inversion results of the corresponding stratigraphic structure. The high-velocity layer at a depth of 200 meters and the rock basement below a depth of 800 meters can be clearly seen in the figure.

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

Claims

1. A method for scanning stratum structure based on a six-component seismograph at a single station, the steps comprising: S1: Select one or more measuring points in the target area; Single-station six-component seismographs are installed at each measuring point to collect passive source signals; Alternatively, a single-station six-component seismograph can be installed at each measuring point to collect passive source signals; S2: pre-process the passive source signal collected from each measuring point to obtain the six-component data of the passive source signal of the corresponding measuring point; calculate the horizontal components of translation and rotation according to the six-component data of the passive source signal, and save the position information of the measuring point; S3: According to the component data characteristics of the six-component data of the passive source signal of the measuring point and the relationship characteristics between the component data, the phase velocity dispersion curve at the measuring point is extracted to obtain the quantitative relationship between the phase velocity and the frequency; S4: Calculating the relative velocity at different frequency points of the corresponding measuring point according to the phase velocity dispersion curve and the quantitative relationship; S5: establishing a mapping relationship between relative velocity and depth according to the quantitative relationship, and obtaining the underground structure of the corresponding measuring point; S6: According to the underground structure of each measuring point in the target area, the stratigraphic profile information drawing or underground three-dimensional structure inversion of the target area is completed.

2. The method according to claim 1, characterized in that The collected passive source signal is recorded as 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) is the horizontal component of the passive source translation data, a z (t) is the vertical component of the passive source translation data, r x (t), r y (t) is the horizontal component of the passive source rotation data, r z (t) is the vertical component of the passive source rotation data; according to the six-component data a′ of the passive source signal after preprocessing x (t), a′ y (t), a′ z (t), r′ x (t), r′ y (t), r′ z (t) Calculate the horizontal component a′ of the translation T (t) and the horizontal component of rotation r′ T (t).

3. The method according to claim 2, characterized in that The horizontal component of translation a ′ T (t) = a ′ x (t)sinθ+a ′ y (t)cosθ, horizontal component of rotation r ′ T (t) = r ′ x (t)sinθ+r ′ y (t)cosθ; where θ is the back azimuth of the incoming wave.

4. The method according to claim 2, characterized in that: The method for preprocessing the passive source signal is: aligning the data time step of the passive source signal in sequence, removing singular value points and human factors in the measurement, and removing the data trend; in Methods for removing singular value points include but are not limited to Grubbs criterion, outlier detection, normalization, clustering, and 3-σ principle methods.

5. The method according to claim 2 or 3, characterized in that: The phase velocity dispersion curve v(f) at the measuring point is obtained using damped least squares method, genetic algorithm, Bayesian algorithm or single-point interferometry.

6. The method according to claim 1, 2 or 3, characterized in that: According to the formula Calculate the corresponding measurement point at different frequencies f k The relative velocity v ′ (f k );in, Where v(f k ) is the kth frequency point f k The corresponding phase velocity is k=1~K, where K is the total number of frequency points.

7. The method according to claim 1, 2 or 3, characterized in that: The mapping relationship v'(d) between the relative velocity v' and the depth d is obtained based on the half-wavelength theory or the skin effect.

8. The method according to claim 1, characterized in that The method for installing the single-station six-component seismograph at the measuring points is as follows: align the directions of the x-component, y-component and z-component of the translation and rotation of the single-station six-component seismograph with the north-south, east-west and up-down directions respectively, and the positive direction of the z-component points to the direction opposite to the gravity acceleration at the measuring point.

9. The method according to claim 1, characterized in that: The multiple measuring points selected in the target area form a measuring line or a measuring point array. When collecting data for multiple measuring points, only a six-component seismograph at a single station is required to perform measurements in sequence.

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