Passive source and active source rayleigh wave combined exploration method and system

Abstract

The present application is suitable for the field of seismic surface wave exploration technology, and provides a passive source and active source Rayleigh wave combined exploration method and system, comprising the following steps: collecting data, the data including passive source data and active source data, uniformly using 200-300Hz sampling rate; processing data, processing the passive source data and active source data, and separately storing the active source data of each excitation point; calculating cross-correlation function and cylindrical wave dispersion. According to the present application, the passive source data and the active source data of each excitation point outside the array grouping are flexibly combined according to the array grouping, the array grouping cross-correlation function is jointly calculated, the dispersion energy graph is calculated using the cylindrical wave algorithm, the construction method is improved, the data processing is efficient, the signal-to-noise ratio of the data and the accuracy of the dispersion curve measurement are greatly improved, a feasible construction scheme and data processing algorithm are provided, and prospective research is carried out for the development of passive source and active source Rayleigh wave combined detection technology and the introduction of related regulations.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of seismic surface wave exploration, and particularly relates to a passive source and active source Rayleigh wave combined exploration method and system. BACKGROUND

[0002] Seismic surface waves include Rayleigh waves and Love waves. The trajectory of the Rayleigh wave particle motion is a retrograde ellipse, and it contains both vertical and horizontal components. The Rayleigh wave is more sensitive to the shallow low-velocity layer and heterogeneity, and the vertical component is also easier to excite and observe. Therefore, the Rayleigh wave is more widely used in exploration applications, such as engineering investigation, geological disaster investigation, geological investigation, resource exploration, urban underground space geophysical exploration, etc.

[0003] According to the different properties of the source, Rayleigh wave exploration can be divided into microtremor detection (passive source) and transient surface wave detection (active source). Different technical procedures are performed. The microtremor detection observes the background noise data in the natural environment for several minutes to several hours, and uses non-interference method (beamforming algorithm) or interference method (cross-correlation algorithm) to obtain the Rayleigh wave dispersion curve. The transient surface wave detection excites a pulse sub-wave by artificial excitation (hammering or mechanical ramming), and obtains the Rayleigh wave seismic record for a short time of several seconds. The non-interference method (refraction method of superimposed amplitude) or interference method (cross-correlation algorithm) is used to obtain the Rayleigh wave dispersion curve. The passive source microtremor detection and the active source transient surface wave detection are both for obtaining the Rayleigh wave dispersion curve corresponding to the geological structure of the detection area, but there are also the following obvious differences:

[0004] (1) The passive source observation array can be a linear array or an arbitrary type of array. The active source observation array is usually a linear array.

[0005] (2) The passive source observation array has a long observation time, which depends on the detection depth and the size of the designed array. Usually, the background noise data for tens of minutes to tens of hours is observed. The active source observation array has a short observation time. After the array is laid out, only a few seconds of data after excitation needs to be observed.

[0006] (3) The sampling rates are different. Because the passive source observation time is long and the data volume is large, the Rayleigh wave dispersion energy obtained is usually <35Hz. Therefore, the passive source observation sampling rate is set to 100~200Hz. The active source observation time is only a few seconds, and the high frequency of the Rayleigh wave dispersion energy obtained can reach about 100Hz. Therefore, the active source observation sampling rate is usually set to 2000Hz, 4000Hz or even higher.

[0007] The passive source detection and the active source detection of the Rayleigh wave can respectively obtain a part of the theoretical dispersion curve of the underground structure (such as Figure 1 , Figure 2As shown in the figure, the dispersion curves obtained by passive source detection are relatively lower frequency and have the advantage of greater detection depth, while the dispersion curves obtained by active source detection are biased towards the higher frequency band and have higher detection resolution for shallow structures. However, there is a risk of overgeneralization when inverting geological structures from local dispersion curves, which may increase the uncertainty of the inversion results. In addition, if passive source detection and active source detection are carried out separately, the instrument sampling rate needs to be changed, which increases the working time cost. Without changing the sampling rate, it is necessary to set up a high sampling rate scheme to observe passive and active sources at the same time, which greatly increases the amount of passive source observation data, such as from hundreds of Mb data to several Gb data, which is unnecessary. For linear arrays, passive source detection is also affected by non-stable phase region noise sources that deviate from the line, causing the phase velocity of the dispersion curve to be overestimated, resulting in inaccurate subsurface structure.

[0008] Currently, the combined use of passive and active source Rayleigh surface waves in existing technologies involves: separately processing passive source observation data (typically tens of minutes to several hours) to calculate the cross-correlation function and dispersion curve, and processing active source primary excitation data (typically a few seconds) to calculate the dispersion curve, and then using... Figure 3 As shown, the dispersion curves of the passive and active sources are weighted, spliced, and smoothed to obtain the dispersion curve for the combined use of Rayleigh surface waves (e.g., Figure 4 As shown in the figure, the above scheme has significant drawbacks, including issues with the sampling rate settings of the observation instruments, overestimation of the phase velocity of the passive source data dispersion curve of the linear array, and inversion errors caused by the fact that the splicing of the passive and active source dispersion curves does not always match. Summary of the Invention

[0009] The purpose of this invention is to provide a method for joint exploration of passive and active Rayleigh surface waves, aiming to solve the problems existing in the background art.

[0010] The present invention is implemented as follows: a method for joint exploration of passive and active source Rayleigh surface waves includes the following steps:

[0011] Data is collected, including passive source data and active source data, all using a sampling rate of 200-300Hz.

[0012] The data is processed by combining passive and active source data, with the active source data from each excitation point stored separately.

[0013] Calculate the cross-correlation function and the cylindrical wave dispersion.

[0014] Preferably, the data acquisition step, which includes passive source data and active source data, and uses a sampling rate of 200-300Hz, specifically includes:

[0015] Several instruments are arranged in an observation array, which is linear or approximately linear, and the sampling rate of the instruments is set to 200-300Hz;

[0016] First, passive source data is observed for tens of minutes to hours, then a main active source is excited from one side of the observation array as a collection point, then a main active source is excited every several instruments inside the array, and finally a main active source is excited from the other side of the observation array.

[0017] Preferably, the collection point continuously excites the main active source for 10-16 times, and the time interval of each excitation is 10-12s.

[0018] Preferably, the step of processing data and processing passive source data and main active source data to obtain the cross-correlation function specifically includes:

[0019] The main active source data is cut into a group of data according to each collection point, and the excited main active source signal and the passive source signal in the previous and subsequent time are continuously cut and saved into a data file;

[0020] The observed passive source data and the main active source data of each collection point are saved into separate data files;

[0021] After the array is grouped according to the detection depth, the data is adjusted and calculated according to the grouping condition.

[0022] Preferably, the step of adjusting and calculating the data according to the grouping condition after the array is grouped according to the detection depth specifically includes: adjusting the passive source data and the main active source data outside the group after the array is grouped, merging the passive source data and the adjusted multiple main active source data according to the arrangement order, and then performing conventional preprocessing, data grouping according to time length, cross-correlation calculation and stacking to obtain the cross-correlation function.

[0023] Preferably, the step of calculating the cross-correlation function and the cylindrical wave dispersion specifically includes:

[0024] The cross-correlation function is as follows:

[0025] (1);

[0026] In formula (1), is the cross-correlation function between A and B, is the signal recorded by station A, is the signal recorded at station B, t is time, τ is the integration variable, the positive branch of the cross-correlation of the seismic signal recorded at point A with the seismic signal recorded at point B is the empirical Green's function from point A to point B, after obtaining the empirical Green's function, the phase velocity or group velocity of the surface wave is measured therefrom, the discrete expression of formula (1) in the time domain is obtained, so as to realize the cross-correlation calculation in the time domain through programming, or the cross-correlation result is obtained through the conjugate calculation of the signal and the inverse Fourier transform in the frequency domain;

[0027] The dispersion energy is calculated by using the cylindrical wave phase shift method.

[0028] Preferably, the step of calculating the dispersion energy by using the cylindrical wave phase shift method specifically comprises:

[0029] The particle vibration displacement record of the point source excitation in the time domain is the convolution of the point source wavelet and the Green's function, and in the frequency domain, it is the multiplication of the two, and the frequency domain particle vibration displacement record of the point source with a distance of r from the point source is is expressed as:

[0030] (2)

[0031] In formula (2), is the spectrum of the wavelet, is the Green's function; is the circular wave number at the circular frequency of the surface wave, and its mathematical form is , is the phase velocity of the surface wave at the circular frequency ; is the imaginary unit, is the phase angle related to and ; is the initial phase of the point source at the circular frequency ;

[0032] Considering two recording points A and B with a distance of and from the point source respectively and being collinear, taking A as the reference, the cross-correlation function spectrum between the two at the circular frequency is:

[0033] (3)

[0034] In formula (3), is the spectrum of the cross-correlation function, and the symbol represents the conjugate operation;

[0035] The cross-correlation removes the initial phase of the point source, so the real part and the imaginary part of the cross-correlation function spectrum are used to calculate the dispersion spectrum , and the expression is:

[0036] (4)

[0037] In formula (4), is the touch phase, and the distance of the recording point to the virtual source and the touch circular wave number ; symbols and respectively represent the real part and the imaginary part of the cross-correlation function spectrum;

[0038] Touch phase based on cylindrical wave dispersion mechanism The expression is:

[0039] (5)

[0040] When the touch phase is completely equal to , the integral function in formula (4) reaches the maximum value, and the surface wave phase velocity is picked up according to the energy peak value in the dispersion spectrum image.

[0041] Another purpose of the embodiment of the application is to provide a passive source and active source Rayleigh wave joint exploration system for realizing the passive source and active source Rayleigh wave joint exploration method, comprising:

[0042] The acquisition unit is used for acquiring data, and the data includes passive source data and active source data, and a sampling rate of 200-300Hz is uniformly used;

[0043] The processing unit is used for processing data, and the passive source data and the active source data are processed, and the active source data of each excitation point is stored separately;

[0044] The calculation unit is used for calculating the cross-correlation function and the cylindrical wave dispersion.

[0045] The passive source and active source Rayleigh wave joint exploration method provided by the embodiment of the application flexibly combines passive source data and active source data outside the group according to array grouping, jointly calculates the group cross-correlation function, and calculates the dispersion energy graph using a more practical cylindrical wave algorithm, and has the following characteristics:

[0046] The construction method is improved, and a new construction method is proposed, in which one active source sampling point is arranged at intervals of several geophones in the case of long line construction, the sampling point accumulates about 10 times of active source excitation, and each excitation interval is about 10 seconds. New construction method, passive source and active source data can be sequentially acquired in one construction process, and dozens or hundreds of passive source+active source Rayleigh wave joint exploration points can be obtained in one construction, compared with the traditional layout and construction method, the construction efficiency is greatly improved.

[0047] The data processing has high efficiency, passive source and active source data can be combined flexibly, high signal-to-noise ratio cross-correlation function of passive source and active source joint data can be calculated at one time, and then high signal-to-noise ratio dispersion energy map is output at one time, the dispersion curve generated by passive source and active source data is directly extracted, and the multi-step process of respectively calculating the dispersion curves of passive source and active source and then splicing passive source and active source dispersion curves is avoided;

[0048] The signal-to-noise ratio of data and the accuracy of dispersion curve measurement are greatly improved, the fundamental and high-order dispersion curves obtained by joint detection of passive source and active source are more easily distinguished on the dispersion energy map, so that the mode misjudgment of the dispersion curve is avoided from the source, and the joint detection method is compared with the prior art, and the frequency bands of the fundamental and high-order dispersion are wider and more abundant, thereby providing a solid foundation for accurate inversion of geological structure;

[0049] A feasible construction scheme and data processing algorithm are provided, and the feasibility is verified through a case, and a prospective research is carried out for the development of passive source and active source Rayleigh wave joint detection technology and the promotion of related regulations. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 It is a theoretical model (a) of underground structure in the prior art and a theoretical dispersion curve (b) generated by forward modeling of the theoretical model;

[0051] Figure 2 It is a dispersion curve (a) obtained by passive source detection and a dispersion curve (b) obtained by active source detection in the prior art;

[0052] Figure 3 It is a comparison diagram of the theoretical dispersion curve, the dispersion curve obtained by passive source detection and the dispersion curve obtained by active source detection in the prior art;

[0053] Figure 4 It is a dispersion calculation and splicing processing schematic diagram of passive source and active source in the prior art (a is passive source dispersion, b is active source dispersion, and c is passive source+active source splicing dispersion, according to Cheng et al., 2016);

[0054] Figure 5 It is passive source observation data and its spectrum provided by the embodiment of the application;

[0055] Figure 6 It is active source observation data and its spectrum provided by the embodiment of the application;

[0056] Figure 7 It is an observation system schematic diagram provided by the embodiment of the application;

[0057] Figure 8The 13 active source excitation signals (01.Z in the figure is the vertical Z component data of the No. 01 instrument in the observation system, and the data of the instruments numbered 41-99 are not shown due to the limited display length) continuously collected by the observation system S1 provided for the embodiment of the present application;

[0058] Figure 9 The array layout for collecting data when applying the detection analysis in a certain place provided for the embodiment of the present application;

[0059] Figure 10 The passive source data (5-minute measurement data) of part of the instruments provided for the embodiment of the present application;

[0060] Figure 11 The 16 excitation collection data of one active source collection point (the collection point is located in the middle of EB002119 and EB002120) provided for the embodiment of the present application;

[0061] Figure 12 The cross-correlation function (left figure) and the dispersion energy graph (right figure) obtained by using the passive source data in the prior art by using the traditional method;

[0062] Figure 13 The cross-correlation function (left figure) and the dispersion energy graph (right figure) obtained by combining the passive source data and the active source data provided for the embodiment of the present application;

[0063] Figure 14 The flowchart of the passive source and active source Rayleigh wave joint exploration method provided for the embodiment of the present application;

[0064] Figure 15 The structural block diagram of the passive source and active source Rayleigh wave joint exploration system provided for the embodiment of the present application. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0066] The passive source and active source data and the spectrum analysis thereof after using the same set of instrument layout are shown in FIGS. 1 and 2, the observation array is a linear array, the number of instruments is 30, the inter-station distance is 1 m, in order to simultaneously observe the passive source and the active source, the sampling rate of the instruments is uniformly set to 2000 Hz, the passive source observation time is 40 min (2600 s), the single excitation observation time of the active source is recorded as 1 s, through the dispersion analysis of the observation data, it can be known that the main energy segment frequency of the passive source is <30 Hz (7-17 Hz), and the main energy segment frequency of the active source is >20 Hz (30-80 Hz); Figure 5 、 Figure 6 ​

[0067] Analysis shows that the frequencies used for active and passive source exploration are basically between 1-100Hz. According to the Nyquist sampling theorem, in order to recover the original signal from a continuous signal without distortion, the sampling frequency must be no less than twice the highest frequency of the signal. In other words, when the sampling rate of the nodal seismograph used for exploration is set to 200Hz or slightly higher, it can be guaranteed that the frequency range used for active and passive source surface wave exploration can be extracted. Therefore, the sampling rate in this embodiment of the invention can be set to around 200Hz.

[0068] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0069] like Figure 14 The diagram shown is a flowchart of a combined passive and active source Rayleigh surface wave exploration method according to an embodiment of the present invention, which specifically includes the following steps:

[0070] S1. Data collection: such as... Figure 7 As shown, the linear array can be configured with any number of instruments. The observation system array in the figure consists of 99 instruments arranged linearly or approximately linearly. The channel spacing between adjacent instruments can be equal or unequal. In actual observation, RTK is used to measure the precise coordinates of the instruments. The sampling rate of the instruments is set to 200-300Hz. During data acquisition, passive source data is observed for tens of minutes to several hours. Then, active source data is collected starting from one side of the observation array, as shown in the figure, numbered S1. Active source is then excited every few instruments inside the array. For example, active source S2 is excited between instruments 9 and 10, active source S3 is excited between instruments 19 and 20, and so on. Active source S9 is excited between instruments 79 and 80, active source S10 is excited between instruments 89 and 90, and finally, active source S11 is excited on the other side of the observation array.

[0071] Unlike traditional active sources that excite an active source once at each measurement point (e.g.) Figure 6 (Left figure) Unlike data acquisition using a higher sampling rate such as 2000Hz, this embodiment of the invention allows both the active and passive sources to use a sampling rate of 200-300Hz when acquiring data, reducing the process of changing the sampling rate when the instrument is used for passive and active source construction.

[0072] To better utilize the active source excitation data and obtain a high signal-to-noise ratio joint dispersion, the design involved approximately 10 excitations of the active source at each excitation point, with each excitation interval controlled to be around 10 seconds. The results are as follows. Figure 8 As shown, in Figure 8 The active source excitation signal was continuously collected 13 times at point S1. The active source collection time was concentrated between 9:52 and 9:54, about two minutes.

[0073] S2, processing data: cutting the active source data into a group of data according to each acquisition point, such as Figure 8 S1 acquisition point, cutting and saving the excited 13 times of active source signals and passive source signals in a period of time (20s before and after in the embodiment of the application) into a data file, such as S1.sg2 (in addition to sg2 format, other general seismic data file formats can also be used), the data file contains all instruments of the whole array, and in the embodiment of the application, it contains instruments No. 1-99;

[0074] The observed passive source data and the active source data of each acquisition point are saved into separate data files according to the above similar operation, such as BD.sg2, S1.sg2, S2.sg2……S11.sg2, after the array is grouped according to the detection depth, codes can be written to adjust the data according to the grouping condition to carry out calculation and analysis, specifically, because the subarray inside the group cannot have an active source, therefore, after the array is grouped, the passive source and the active source data outside the subarray are adjusted, and then the cross-correlation calculation and the dispersion calculation are carried out, such as Figure 7 The subarray is divided according to 30 instruments, that is, 1-30, 2-31, 3-32……70-99 instruments are grouped, and 70 subarrays can be obtained, for example, the first 1-30 instrument subarray, the data of S2, S3 and S4 acquisition points inside the array cannot be adjusted to calculate the cross-correlation function, the passive source data and the active source data outside the subarray can be adjusted, including BD.sg2, S1.sg2, S5.sg2, S6.sg2, S7.sg2, S8.sg2, S9.sg2, S10.sg2 and S11.sg2, and then the conventional pretreatment, data grouping according to time length, cross-correlation calculation and stacking are carried out, and the cross-correlation function is obtained;

[0075] S3, calculating the cross-correlation function and the cylindrical wave dispersion:

[0076] The cross-correlation function is as follows:

[0077] (1);

[0078] In formula (1), is the cross-correlation function between A and B, is the signal recorded by station A, is the signal recorded by station B, t is time, τ is the integration variable; the positive branch of the cross-correlation of the seismic signal recorded at point A and the seismic signal recorded at point B is the empirical Green's function from point A to point B, and only after the empirical Green's function is obtained can the phase velocity or group velocity of the surface wave be measured therefrom. A discrete expression of equation (1) in the time domain can be obtained, so that the cross-correlation calculation can be realized in the time domain through programming, or the cross-correlation result can be obtained in the frequency domain through conjugate calculation and inverse Fourier transform of the signal;

[0079] After the cross-correlation function is obtained, the frequency dispersion energy diagram can be calculated through the phase shift method, the SPAC algorithm for fitting the zero-order Bessel function, etc. Since the traditional frequency dispersion energy algorithm is usually derived based on the assumption of plane wave far field approximation, these passive sources are more suitable. For active sources, the acquired signals are mainly near-field cylindrical waves, and when passive sources and active sources are combined to extract dispersion, the development of cylindrical waves should be fully considered. Therefore, it is recommended to use the cylindrical wave algorithm to calculate the frequency dispersion energy.

[0080] The cylindrical wave phase shift method is used to calculate the frequency dispersion energy: the point source excited particle vibration displacement record in the time domain is the convolution of the point source wavelet and the Green's function, and in the frequency domain, it is the multiplication of the two. Then the frequency domain particle vibration displacement record of the point source with a distance of r from the point source is , which is expressed as:

[0081] (2)

[0082] In equation (2), is the spectrum of the wavelet, is the Green's function; is the circular wave number at the circular frequency , and its mathematical form is , is the surface wave phase velocity at the circular frequency ; is the imaginary unit, is the phase angle related to and ; is the initial phase of the point source at the circular frequency ;

[0083] Considering two recording points A and B with a distance of and from the point source respectively and being collinear, taking A as the reference (virtual source), the cross-correlation function spectrum between the two at the circular frequency is:

[0084] (3)

[0085] In equation (3), is the spectrum of the cross-correlation function, and the symbol representing the conjugate operation;

[0086] The cross-correlation removes the initial phase of the point source, so the real and imaginary parts of the cross-correlation function spectrum can be used to calculate the dispersion spectrum respectively , the expression is:

[0087] (4)

[0088] In formula (4), is the touch phase, which is related to the distance from the recording point to the virtual source and the touch circular wave number ; the symbols and respectively represent the real part and the imaginary part of the cross-correlation function spectrum;

[0089] In surface wave imaging, the vertical component of the seismic signal is usually collected, and the touch phase based on the cylindrical wave diffusion mechanism The expression is:

[0090] (5)

[0091] When the touch phase is completely equal to , the integral function in formula (4) reaches the maximum value, and the surface wave phase velocity is picked up according to the energy peak value in the dispersion spectrum image.

[0092] As shown in Figure 15 , a structure block diagram of a passive source and active source Rayleigh wave combined exploration system provided by an embodiment of the present application is provided, and specifically includes:

[0093] The acquisition unit 100 is used for acquiring data, and the data includes passive source data and active source data, and a sampling rate of 200-300Hz is uniformly used;

[0094] The processing unit 200 is used for processing data, and the passive source data and the active source data are processed, and the active source data of each excitation point is stored separately;

[0095] The calculation unit 300 is used for calculating the cross-correlation function and the cylindrical wave dispersion.

[0096] In a certain place, the method proposed in the embodiment of the present application is used for exploration analysis, and the array arrangement is as shown in Figure 9 , 107 instruments are arranged at one time, the average inter-station distance is 1m (the accurate coordinates are measured by RTK), the passive source is collected for 30min, the active source is collected for 12 points, each point is excited for about 10 times, the active source collection time of each point is about 2min, and the sampling rate of the instrument is uniformly set to 250Hz, and part of the passive source data of the instrument is as shown in Figure 10As shown, one active source acquisition point 16 times excitation acquisition data such as Figure 11 As shown;

[0097] Using 30 channels of instrument for an array, selecting one sub-array to calculate the passive source cross-correlation function using traditional method, and using phase shift method to calculate the dispersion energy map from the cross-correlation function such as Figure 12 As shown, Figure 12 It can be seen that the energy focusing dispersion curve is mainly distributed in 5-40Hz, and the energy group focusing near 20Hz is broken; using the method proposed in the embodiment of the application, using Figure 10 Passive source data and several active source acquisition point data similar to Figure 11 (not including the active source acquisition point data located in the array), calculating the cross-correlation function after data merging, the result is shown as Figure 13 As shown;

[0098] As shown, Figure 12 and Figure 13 It can be seen that the cross-correlation function calculated by the new method combining passive source and active source proposed in the embodiment of the application has higher signal-to-noise ratio, the Rayleigh wave dispersion signal is clearer, the dispersion energy map calculated has significantly improved signal-to-noise ratio, the noise signal is effectively suppressed, and the dispersion energy signal is significantly enhanced; the dispersion energy map obtained by the traditional method has overlapping and broken dispersion curves near 20Hz, and the fundamental and high-order dispersion curves cannot be correctly identified, while the dispersion energy map obtained by the new method combining passive source and active source proposed in the embodiment of the application has not only clear fundamental and high-order dispersion energy, but also obvious distinction between the fundamental and high-order, reducing the identification error of dispersion curve order; in addition, the frequency band of the dispersion curve of the fundamental and high-order obtained by the method of the embodiment of the application is wider, the traditional method has fundamental about 7-19Hz and high-order about 20-37Hz, the method of the embodiment of the application has fundamental band expanded to 7-30Hz and high-order band expanded to 20-45Hz.

[0099] In summary, the method and system provided by the embodiment of the application, passive source and active source joint exploration unified setting instrument sampling rate 200-300Hz, the sampling rate does not need to be changed in the construction process, and it does not need to be set like the traditional passive source and active source exploration, respectively, the passive source sampling rate is set to 200Hz, the instrument sampling rate is changed to be higher, such as 2000Hz, if the instrument does not have 4G function, it is very tedious and time-consuming to change the sampling rate of each instrument one by one; A new construction method is proposed, in which a active source sampling point is set at intervals of several detectors in the long measuring line construction, the active source is excited about 10 times at the sampling point, and each excitation interval is about 10s, dozens or hundreds of passive source+active source Rayleigh wave joint exploration points can be obtained at a time, compared with the traditional active source station and construction method that can only excite at both ends of the measuring line, the construction efficiency is greatly improved.

[0100] A data combination processing method for passive source and active source joint construction is proposed, that is, the observation passive source data of all instruments of the measuring line and the multi-excitation active source data of each sampling point are extracted respectively, the passive source data and the active source data of each sampling point outside the subarray are flexibly combined according to the subarray condition after the measuring line is grouped, and the active source data of each sampling point is efficiently utilized. Since the active source excited by each sampling point is different from the distance of the subarray, the subarray contains rich surface wave signals of different frequency bands.

[0101] The passive source and active source joint data contain rich Rayleigh wave signals of each frequency band, the signal-to-noise ratio of the calculated cross-correlation function is significantly improved, and since the active source excitation of the sampling point is in the observation measuring line and the extension line, the phase velocity of the obtained frequency dispersion energy avoids the error introduced by the bias noise source in the pure passive source observation, and the measured phase velocity is more accurate.

[0102] For passive source and active source observation data, the main cylindrical wave in the near-field active source excitation is fully considered, the cylindrical wave phase shift method is used to calculate the frequency dispersion energy graph, the introduction of the cylindrical wave algorithm is more consistent with the actual situation than other algorithms assuming the far-field plane wave, and the measured frequency dispersion curve phase velocity is more accurate.

[0103] The base order and high order of the frequency dispersion curve obtained by the new passive source and active source Rayleigh wave joint exploration method are more easily distinguished, and the frequency band of the base order and high order frequency dispersion curve is wider, which provides a solid foundation for accurate inversion of geological structure;

[0104] The embodiment of the application demonstrates the feasibility of passive source and active source Rayleigh wave joint detection from the construction condition and calculation theory, and carries out forward-looking research for the development of passive source and active source Rayleigh wave joint detection technology and the introduction of related regulations.

[0105] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for joint exploration of passive and active source Rayleigh surface waves, characterized in that, Includes the following steps: Data is collected, including passive source data and active source data, all using a sampling rate of 200-300Hz. The data is processed by combining passive and active source data, with the active source data from each excitation point stored separately. Calculate the cross-correlation function and cylindrical wave dispersion; The data acquisition step, which includes both passive and active source data and uses a uniform sampling rate of 200-300Hz, specifically includes: Several instruments are set up in the observation array, arranged linearly or approximately linearly, and the sampling rate of the instruments is set to 200-300Hz. First, observe passive source data for tens of minutes to several hours. Then, use an active source as a collection point outside one side of the observation array. Next, use active sources every few instruments inside the array. Finally, use active sources outside the other side of the observation array. The data processing involves processing passive and active source data, with active source data from each excitation point stored separately. This process includes: grouping the array according to the detection depth, and then loading the data for calculation and analysis based on the grouping. Specifically, this includes: loading passive source data and active source data from outside the group after array grouping, merging the passive source data and the loaded active source data in the order of arrangement, and then performing routine preprocessing, grouping the data by duration, cross-correlation calculation, and superposition to obtain the cross-correlation function. The steps for calculating the cross-correlation function and cylindrical wave dispersion include: the steps for calculating the dispersion energy using the cylindrical wave phase shift method, specifically including: The displacement record of particle vibration excited by a point source is the convolution of the point source wavelet and the Green's function in the time domain, and the product of the two in the frequency domain. This is the displacement record of the particle vibration in the frequency domain at a distance r from the point source. Represented as: （2） In equation (2), It is the spectrum of the wavelet. It is the Green's function; The angular frequency is The circular wave number at a given point is expressed in mathematical form as follows: , The angular frequency is Surface wave phase velocity at the location; It is the imaginary unit. To and and The relevant phase angle; The angular frequency is The initial phase of the point source at that location; Considering the distances from the point source as follows: and And for two collinear recording points A and B, with A as the reference, the angular frequency is... The spectrum of the cross-correlation function between the two at point A is: （3） In equation (3), It is the spectrum of the cross-correlation function, with the sign... Represents the conjugate operation; Cross-correlation removes the initial phase of the point source; therefore, the dispersion spectrum is calculated using the real and imaginary parts of the cross-correlation function's spectrum, respectively. The expression is: （4） In equation (4), It is the trial phase, and the distance from the recording point to the virtual source. and the number of circular waves Related; symbols and These represent the real and imaginary parts of the spectrum of the cross-correlation function, respectively. Trial phase based on cylindrical wave diffusion mechanism The expression is: （5） When the phase of the trial contact and When they are completely equal, the integrand in formula (4) reaches its maximum value, and the surface wave phase velocity is picked up based on the energy peak in the dispersion spectrum image.

2. The method for joint exploration of passive and active source Rayleigh surface waves according to claim 1, characterized in that, The collection point is continuously excited by the active source 10-16 times, with an interval of 10-12 seconds between each excitation.

3. The method for joint exploration of passive and active source Rayleigh surface waves according to claim 1, characterized in that, The data processing involves processing both passive and active source data, and storing the active source data from each excitation point separately. Specifically, this includes: The active source data is divided into a set of data according to each acquisition point, and the continuously excited active source signals and the passive source signals of the preceding and following time periods are continuously cut and saved into a data file. Both the passive source data observed and the active source data from each acquisition point are saved as separate data files; After grouping the array according to the detection depth, the data is retrieved for calculation and analysis based on the grouping.

4. The method for joint exploration of passive and active source Rayleigh surface waves according to claim 1, characterized in that, The steps for calculating the cross-correlation function and cylindrical wave dispersion specifically include: The cross-correlation function is given by the following formula: （1）； In equation (1), It is the cross-correlation function between A and B. This is the signal recorded by station A. The signal is recorded by station B, t is time, τ is the integral quantity, and the positive branch of the cross-correlation result between the seismic signal recorded at point A and the seismic signal recorded at point B is the empirical Green's function from point A to point B. After obtaining the empirical Green's function, the phase velocity or group velocity of the surface wave is measured from it to obtain the discrete expression of equation (1) in the time domain. Thus, the cross-correlation calculation is realized in the time domain through programming, or the cross-correlation result is obtained in the frequency domain through the conjugate calculation of the signal and the inverse Fourier transform. The dispersion energy was calculated using the cylindrical wave phase shift method.

5. A passive and active source Rayleigh surface wave joint exploration system, used to implement the passive and active source Rayleigh surface wave joint exploration method as described in any one of claims 1-4, characterized in that, include: The acquisition unit is used to acquire data, which includes passive source data and active source data, and uses a uniform sampling rate of 200-300Hz. The processing unit is used to process data, including passive source data and active source data, with active source data from each excitation point stored separately. The calculation unit is used to calculate the cross-correlation function and the cylindrical wave dispersion.

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