Passive source and active source Rayleigh surface wave combined exploration method and system

Abstract

The invention is suitable for the technical field of seismic surface wave exploration, and provides a passive source and active source Rayleigh surface wave joint exploration method and system, and the method comprises the following steps: collecting data which comprise passive source data and active source data, and uniformly employing a 200-300 Hz sampling rate; processing the data, processing the passive source data and the active source data, and independently storing the active source data of each excitation point; and calculating a cross-correlation function and cylindrical wave dispersion. According to array grouping flexible combination passive source data and active source data of each excitation point outside the array grouping, an array grouping cross-correlation function is jointly calculated, and a frequency dispersion energy diagram is calculated by using a cylindrical wave algorithm; the construction method is improved, data processing is efficient, the signal-to-noise ratio of data and the accuracy of frequency dispersion curve measurement are greatly improved, a feasible construction scheme and a feasible data processing algorithm are provided, and prospective research is developed for development of a passive source and active source Rayleigh surface wave combined detection technology and promotion of related regulations.

Description

Technical Field

[0001] The invention belongs to the technical field of seismic surface wave exploration, and in particular relates to a passive source and active source Rayleigh surface wave joint exploration method and system. Background Art

[0002] Seismic surface waves include Rayleigh surface waves and Love surface waves. The motion trajectory of Rayleigh wave particles is a retrograde ellipse, which contains both vertical and horizontal components. Rayleigh surface waves are more sensitive to shallow low-velocity layers and inhomogeneities, and the vertical component is easier to excite and observe. Therefore, Rayleigh surface waves are more widely used in exploration applications, such as engineering surveys, geological disaster investigations, geological surveys, resource exploration, and urban underground space geophysical exploration.

[0003] According to the different properties of the earthquake source, Rayleigh surface wave exploration can be divided into micromotion detection (passive source) and transient surface wave detection (active source), and different technical procedures are implemented respectively. Micromotion detection obtains Rayleigh surface wave dispersion curves by observing background noise data in the natural environment for several minutes to tens of hours using non-interference method (beaming algorithm) or interference method (cross-correlation algorithm); transient surface wave detection obtains Rayleigh surface wave seismic records of a few seconds by artificially exciting (hammering or mechanical tamping) a pulse wavelet, and obtains Rayleigh surface wave dispersion curves using non-interference method (refraction method of superimposed amplitude) or interference method (cross-correlation algorithm). Both passive source micromotion detection and active source transient surface wave detection are aimed at obtaining Rayleigh surface wave dispersion curves corresponding to the geological structure of the detection area, but there are also obvious differences in the following aspects:

[0004] (1) Passive source observation arrays can be linear arrays or arrays of any type; active source observation arrays are usually linear arrays;

[0005] (2) The observation time of a passive source observation array is relatively long, depending on the detection depth and the size of the designed array. It usually takes tens of minutes to tens of hours to observe background noise data. The observation time of an active source observation array is relatively short. After the array is deployed, it only needs to observe a few seconds of data after the excitation.

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

[0007] Passive and active source detection of Rayleigh surface waves can respectively obtain a part of the theoretical dispersion curve of underground structure (such as Figure 1 , Figure 2As shown in the figure, relatively speaking, the dispersion curve obtained by passive source detection is lower in frequency and has the advantage of a large detection depth, while the dispersion curve obtained by active source detection is biased towards the high frequency band, and has a higher detection resolution for shallow structures. However, there is a risk of generalizing the geological structure from the local dispersion curve, which may increase the uncertainty of the inversion result. In addition, if passive source detection and active source detection are implemented separately, the instrument sampling rate needs to be changed, which increases the working time cost. Without changing the sampling rate, a high sampling rate solution is required 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 to several Gb, which is not necessary. For linear arrays, passive source detection is also affected by the noise source in the non-stable phase zone of the deviation line, which causes the phase velocity of the dispersion curve to be overestimated, resulting in inaccurate underground structure.

[0008] At present, the passive source and active source Rayleigh surface waves are used together in the existing technology. The method adopted is: separately process the passive source observation data (usually tens of minutes to hours) to calculate the cross-correlation function and dispersion curve and the active source one-time excitation data (usually a few seconds) to calculate the dispersion curve, and then use Figure 3 The passive and active source dispersion curves are weighted and smoothed to obtain the dispersion curve used in conjunction with Rayleigh surface waves (e.g. Figure 4 As shown in the figure, the above scheme has major defects, including problems with the sampling rate setting of the observation instrument, overestimation of the phase velocity of the dispersion curve of the passive source data 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 each other. Summary of the invention

[0009] The purpose of the embodiments of the present invention is to provide a passive source and active source Rayleigh surface wave joint exploration method, aiming to solve the problems existing in the above-mentioned background technology.

[0010] The embodiment of the present invention is implemented as follows: a passive source and active source Rayleigh surface wave joint exploration method, comprising the following steps:

[0011] Collecting data, including passive source data and active source data, using a uniform sampling rate of 200-300 Hz;

[0012] Processing data: processing passive source data and active source data, and storing active source data of each excitation point separately;

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

[0014] Preferably, the step of collecting data, wherein the data includes passive source data and active source data, and uniformly using a sampling rate of 200-300 Hz, specifically includes:

[0015] Several instruments are deployed in the observatory array, the array is arranged linearly or approximately linearly, and the sampling rate of the instruments is set to 200-300Hz;

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

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

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

[0019] The active source data is cut into a set of data according to each acquisition point, and the excited active source signal and the passive source signal of a period of time before and after are continuously cut and saved into a data file;

[0020] The observed passive source data and active source data of each acquisition point are saved as separate data files;

[0021] After the array is grouped according to the detection depth, the data is called in for calculation and analysis based on the grouping situation.

[0022] Preferably, after the array is grouped according to the detection depth, the step of calling in data for calculation and analysis according to the grouping situation specifically includes: after the array is grouped, the passive source data and the active source data outside the group are called in, the passive source data and the multiple active source data called in are merged in the order of arrangement, and then conventional preprocessing, data grouping by time length, cross-correlation calculation and superposition are performed to obtain a 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 given by the following formula:

[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 by station B, t is time, τ is the integral, 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, thereby realizing the cross-correlation calculation in the time domain, or obtaining the cross-correlation result in the frequency domain through the conjugate calculation of the signal and the inverse Fourier transform;

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

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

[0029] The displacement record of the particle vibration excited by the point source 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. The displacement record of the particle vibration in the frequency domain at a distance r from the point source is It is expressed as:

[0030] (2)

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

[0032] Consider the distances from the point source to be and And two collinear recording points A and B, with A as the reference, the circular frequency is The cross-correlation function spectrum between the two is:

[0033] (3)

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

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

[0036] (4)

[0037] In formula (4), is the touch phase, and the distance from the recording point to the virtual source and the number of test circular waves Related to; Symbol and Respectively represent the real and imaginary parts of the cross-correlation function spectrum;

[0038] Test contact phase based on cylindrical wave diffusion mechanism The expression is:

[0039] (5)

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

[0041] Another object of an embodiment of the present invention is to provide a passive source and active source Rayleigh surface wave joint exploration system, which is used to implement the above-mentioned passive source and active source Rayleigh surface wave joint exploration method, including:

[0042] The acquisition unit is used to acquire data, wherein the data includes passive source data and active source data, and a uniform sampling rate of 200-300 Hz is used;

[0043] A processing unit, used for processing data, processing passive source data and active source data, and storing active source data of each excitation point separately;

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

[0045] The embodiment of the present invention provides a passive source and active source Rayleigh surface wave joint exploration method, which flexibly combines passive source data and active source data outside the group according to array grouping, jointly calculates the group cross-correlation function, and uses a more practical cylindrical wave algorithm to calculate the dispersion energy map, and specifically has the following characteristics:

[0046] The construction method has been improved. In the case of long survey line construction, an active source sampling point is set every several geophones. The sampling point excites the active source about 10 times cumulatively, and the interval between each excitation is about 10 seconds. In this way, passive source and active source data can be collected in sequence during one construction process. Dozens or hundreds of passive source + active source Rayleigh surface wave joint exploration points can be obtained in one construction. Compared with the traditional layout and construction methods, the construction efficiency is greatly improved.

[0047] The data processing is highly efficient and can flexibly combine passive and active source data. The high signal-to-noise ratio cross-correlation function of the combined passive and active source data can be calculated at one time, and then a high signal-to-noise ratio dispersion energy map can be produced at one time. The dispersion curve jointly generated by the passive and active source data can be directly extracted, avoiding the multi-step process of traditional algorithms to calculate the dispersion curves of passive and active sources separately and then splice the combined dispersion curves of passive and active sources.

[0048] The signal-to-noise ratio of the data and the accuracy of dispersion curve measurement have been greatly improved. The fundamental and high-order dispersion curves obtained by the joint detection of passive and active sources are easier to distinguish on the dispersion energy diagram, thus avoiding the misjudgment of the dispersion curve pattern from the source. In addition, the frequency bands of the fundamental and high-order dispersion obtained by the new joint detection method are wider and richer than those obtained by the existing technology, providing a solid foundation for the accurate inversion of geological structure.

[0049] A feasible construction plan and data processing algorithm were provided, and the feasibility was verified through cases. Prospective research was carried out for the development of passive and active source Rayleigh surface wave joint detection technology and the introduction of relevant regulations. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0052] Figure 3 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 Schematic diagram of the calculation and splicing of passive source and active source dispersion in the prior art (a is the passive source dispersion, b is the active source dispersion, and c is the dispersion after splicing the passive source + active source, according to Cheng et al., 2016);

[0054] Figure 5 Passive source observation data and spectrum thereof provided by the embodiment of the present invention;

[0055] Figure 6 Active source observation data and spectrum thereof provided by the embodiment of the present invention;

[0056] Figure 7 A schematic diagram of an observation system provided by an embodiment of the present invention;

[0057] Figure 813 active source excitation signals continuously collected at point S1 of the observation system provided by the embodiment of the present invention (01.Z in the figure is the vertical Z component data of instrument No. 01 in the observation system, and the data of instruments No. 41 to No. 99 are not shown due to the limited display length);

[0058] Fig. 9 A collection array layout diagram for application detection and analysis in a certain place provided by an embodiment of the present invention;

[0059] Fig.10 Passive source data (5 minutes of measurement data) of some instruments provided in the embodiments of the present invention;

[0060] Fig.11 An active source acquisition point provided in an embodiment of the present invention (the acquisition point is located between EB002119 and EB002120) is stimulated 16 times to acquire data;

[0061] Fig.12 The cross-correlation function (left) and dispersion energy diagram (right) obtained using passive source data using traditional methods in the prior art;

[0062] Fig.13 The cross-correlation function (left) and the dispersion energy diagram (right) obtained by combining the passive source and active source data provided by the embodiment of the present invention;

[0063] Fig.14 A flowchart of a passive source and active source Rayleigh surface wave joint exploration method provided by an embodiment of the present invention;

[0064] Fig.15 A structural block diagram of a passive source and active source Rayleigh surface wave joint exploration system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0066] The passive and active source data and spectrum analysis were observed using the same set of instruments. Figure 5 , Figure 6 As shown, the observation array is a linear array, with 30 instruments and a spacing of 1m. In order to observe passive and active sources simultaneously, the instrument sampling rate is uniformly set to 2000Hz, the passive source observation time is 40min (2600s), and the active source single excitation observation time is recorded as 1s. Through the dispersion analysis of the observation data, it can be seen that the main energy segment frequency of the passive source is <30Hz (7-17Hz), while the main energy segment frequency of the active source is >20Hz (30-80Hz);

[0067] After analysis, it can be known that the frequencies used in active source and passive source exploration are basically 1-100 Hz. According to the Nyquist sampling theorem, in order to restore the original signal from a continuous signal without distortion, the sampling frequency must be no less than twice the highest frequency of the signal. That is to say, when the sampling rate of the node seismometer used in the exploration is set at 200 Hz or slightly higher, it can be ensured that the frequency band used in active source and passive source surface wave exploration can be extracted. Therefore, the sampling rate in the embodiment of the present invention can be set at about 200 Hz.

[0068] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0069] like Fig.14 As shown, it is a flowchart of a passive source and active source Rayleigh surface wave joint exploration method provided by an embodiment of the present invention, which specifically includes the following steps:

[0070] S1. Collect data: Figure 7 As shown, any instrument can be arranged in the linear array. In the figure, a total of 99 instruments are arranged in the observation system array. The array is arranged linearly or approximately linearly. The track spacing between two adjacent instruments can be equidistant or unequally spaced. In actual observation, RTK is used to measure the precise coordinates of the arranged instruments. The sampling rate of the instrument is set to 200-300Hz. When collecting data, passive source data is first observed for tens of minutes to several hours, and then active sources are collected from the outside of one side of the observation array, such as number S1 in the figure, and then active sources are stimulated once every several instruments in the array. As shown in the figure, active source S2 is stimulated between instruments No. 9 and No. 10, active source S3 is stimulated between instruments No. 19 and No. 20, and so on. Active source S9 is stimulated between instruments No. 79 and No. 80, active source S10 is stimulated between instruments No. 89 and No. 90, and finally active source S11 is stimulated outside the other side of the observation array.

[0071] Compared with the traditional active source, which excites the active source once at each measuring point (such as Figure 6 Left figure) and using a higher sampling rate such as 2000Hz to collect data is different. In the embodiment of the present invention, the active source and the passive source can uniformly use a sampling rate of 200-300Hz when collecting data, which reduces the process of changing the sampling rate of the instrument during the construction of the passive source and the active source;

[0072] In order to make better use of the active source excitation data and obtain a high signal-to-noise ratio joint dispersion, it is designed to excite the active source about 10 times at each excitation point, and the time interval between each time can be controlled at about 10s. The results are as follows Figure 8 As shown, in Figure 8 The active source excitation signals were collected 13 times continuously at the S1 point, and the active source collection time period was concentrated between 9:52 and 9:54, about two minutes;

[0073] S2. Processing data: Cut active source data into a set of data according to each collection point, such as Figure 8 At the S1 acquisition point shown, the 13 active source signals excited and the passive source signals of a period of time before and after (20 seconds before and after in the embodiment of the present invention) are continuously cut and saved into a data file, such as S1.sg2 (in addition to the sg2 format, other general seismic data file formats can also be used). The data file contains all instruments in the entire array, including instruments No. 1-99 in the embodiment of the present invention;

[0074] The observed passive source data and the active source data of each acquisition point are saved as separate data files according to the above similar operations, such as BD.sg2, S1.sg2, S2.sg2...S11.sg2. After the array is grouped according to the detection depth, the code can be written to call in the data for calculation and analysis according to the grouping situation. Specifically, because there cannot be an active source inside the grouped subarray, the passive source and active source data outside the subarray are called in after the array is grouped, and then the cross-correlation calculation and dispersion calculation extraction are carried out, such as Figure 7 As described, the subarray is divided into 30 instruments, that is, instruments No. 1-30, 2-31, 3-32 ... 70-99 are grouped, and 70 subarrays can be obtained. For example, for the first instrument No. 1-30 subarray, the data of the three acquisition points S2, S3 and S4 inside the array cannot be transferred into the calculation of the cross-correlation function, and the passive source data and the active source data outside the subarray including BD.sg2, S1.sg2, S5.sg2, S6.sg2, S7.sg2, S8.sg2, S9.sg2, S10.sg2 and S11.sg2 can be transferred in, and then conventional preprocessing, data grouping by time length, cross-correlation calculation and superposition, etc. are performed to obtain the cross-correlation function;

[0075] S3. Calculate the cross-correlation function and cylindrical wave dispersion:

[0076] The cross-correlation function is given by the following formula:

[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, and τ is the integral; the positive branch of the cross-correlation result 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. Only after obtaining the empirical Green's function can the phase velocity or group velocity of the surface wave be measured from it. The 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 programming, and the cross-correlation result can also be obtained in the frequency domain through the conjugate calculation of the signal and the inverse Fourier transform;

[0079] After obtaining the cross-correlation function, the dispersion energy diagram can be calculated by the phase shift method, the SPAC algorithm that fits the zero-order Bessel function, etc. Since the traditional dispersion energy algorithm is usually based on the assumption of the far-field approximation of the plane wave, these passive sources are more suitable. For the active source, the collected cylindrical waves are mainly near-field cylindrical waves. When the passive source and the active source are jointly extracted for dispersion, the situation that the cylindrical waves are very developed should be fully considered. Therefore, it is recommended to use the cylindrical wave algorithm to calculate the dispersion energy;

[0080] The dispersion energy is calculated using the cylindrical wave phase shift method: the displacement record of the particle vibration excited by the point source 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 displacement record of the particle vibration in the frequency domain at a distance r from the point source is It is expressed as:

[0081] (2)

[0082] In formula (2), is the spectrum of the wavelet, is the Green’s function; The circular frequency is The circular wave number at , its mathematical form is , The circular frequency is The surface wave phase velocity at ; is an imaginary unit, For and The phase angle involved; The circular frequency is The initial phase of the point source at ;

[0083] Consider the distances from the point source to be and And two collinear recording points A and B, with A as the reference (virtual source), the circular frequency is The cross-correlation function spectrum between the two is:

[0084] (3)

[0085] In formula (3), is the frequency spectrum of the cross-correlation function, symbol represents the conjugation operation;

[0086] Cross-correlation removes the initial phase of the point source, so the dispersion spectrum can be calculated using the real and imaginary parts of the cross-correlation function spectrum respectively. , the expression is:

[0087] (4)

[0088] In formula (4), is the touch phase, and the distance from the recording point to the virtual source and the number of test circular waves Related to; Symbol and Respectively represent the real and imaginary parts of the cross-correlation function spectrum;

[0089] In surface wave imaging, vertical component seismic signals are often collected. At this time, the touch phase based on the cylindrical wave diffusion mechanism is The expression is:

[0090] (5)

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

[0092] like Fig.15 As shown, it is a structural block diagram of a passive source and active source Rayleigh surface wave joint exploration system provided by an embodiment of the present invention, which specifically includes:

[0093] The acquisition unit 100 is used to acquire data, wherein the data includes passive source data and active source data, and a uniform sampling rate of 200-300 Hz is used;

[0094] The processing unit 200 is used to process data, process passive source data and active source data, and store active source data of each excitation point separately;

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

[0096] In a certain place, the method proposed in the embodiment of the present invention is applied to perform exploration and analysis, and the collection array is arranged as follows Fig. 9 As shown in the figure, 107 instruments were deployed at one time, with an average station spacing of 1m (accurate coordinates were measured using RTK), passive source data were collected for 30min, active source data were collected at 12 points, each point was stimulated about 10 times, active source data were collected at each point for about 2min, the instrument sampling rate was uniformly set to 250Hz, and the passive source data of some instruments were obtained as shown in the figure. Fig.10As shown, an active source acquisition point excites 16 times to collect data as shown in Fig.11 As shown;

[0097] The survey lines were grouped into an array using 30 instruments. One of the subarrays was selected to calculate the cross-correlation function of the passive source using the traditional method. The phase shift method was used to calculate the dispersion energy diagram from the cross-correlation function. Fig.12 Said by Fig.12 It can be seen that the dispersion curve of energy focusing is mainly distributed in 5-40Hz, and the energy cluster focused around 20Hz is interrupted; using the method proposed in the embodiment of the present invention, using Fig.10 Passive source data and several similar Fig.11 The active source acquisition point data (the active source acquisition point data located inside the array cannot be merged), and the cross-correlation function is calculated after the data is merged, and the result is as follows Fig.13 As shown;

[0098] Depend on Fig.12 and Fig.13 By comparison, it can be seen that the new method of combining passive sources and active sources proposed in the embodiment of the present invention has a higher signal-to-noise ratio in the calculated cross-correlation function, a clearer Rayleigh surface wave dispersion signal, a significantly improved signal-to-noise ratio in the calculated dispersion energy diagram, the noise signal is effectively suppressed, and the dispersion energy signal is significantly enhanced; in the dispersion energy diagram obtained by the traditional method, the fundamental and high-order dispersion curves are aliased and misinterpreted near 20 Hz, and the fundamental and high-order cannot be correctly identified. In the dispersion energy diagram calculated by the new method of combining passive sources and active sources proposed in the embodiment of the present invention, the fundamental and high-order dispersion energies are not only very clear, but also clearly distinguished from each other, reducing the error in the identification of the order of the dispersion curve; in addition, the frequency bands of the fundamental and high-order dispersion curves obtained by the method in the embodiment of the present invention are wider. The fundamental order of the traditional method is about 7-19 Hz and the high order is about 20-37 Hz. The fundamental order frequency band of the method in the embodiment of the present invention is expanded to 7-30 Hz and the high order frequency band is expanded to 20-45 Hz.

[0099] In summary, the method and system provided by the embodiment of the present invention uniformly set the instrument sampling rate of 200-300Hz for the joint exploration of passive sources and active sources. The sampling rate does not need to be changed during the construction process. It is not necessary to set the passive source sampling rate, such as 200Hz, respectively, like the traditional passive source and active source exploration. When constructing the active source, the instrument sampling rate is changed to a higher rate, such as 2000Hz. If the instrument does not have a 4G function, it is very cumbersome and time-consuming to change the sampling rate of each instrument one by one. In the case of long survey line construction, an active source sampling point is set at intervals of several geophones, and the sampling point excites the active source about 10 times cumulatively, and each excitation interval is about 10s. A new construction method is proposed, in which dozens or hundreds of passive source + active source Rayleigh surface wave joint exploration points can be obtained at one time. Compared with the traditional active source layout and construction method that can only be excited at both ends of the survey line, the construction efficiency is greatly improved.

[0100] A data combination processing method for the joint construction of passive and active sources is proposed, that is, the passive source data of all instruments on the survey line and the multiple-excitation active source data of each sampling point are respectively cut and extracted. According to the sub-array situation after the survey line is grouped, the passive source data and the active source data of each sampling point outside the sub-array are flexibly combined to efficiently use the active source data of each sampling point. Since the active source excited by each sampling point is at different distances from the sub-array, the sub-array contains rich surface wave signals of different frequency bands.

[0101] The combined data of passive and active sources contain abundant Rayleigh surface wave signals in various frequency bands. The signal-to-noise ratio of the calculated cross-correlation function is significantly improved. At the same time, since the active source excitations at the sampling points are all inside the observation line and on the extension line, the phase velocity of the obtained dispersion energy avoids the error introduced by the deflection noise source in the case of pure passive source observation, and the measured phase velocity is more accurate.

[0102] For passive and active source observation data, the main cylindrical waves developed in the near-field active source excitation are fully considered, and the dispersion energy diagram is calculated using the cylindrical wave phase shift method. The introduction of the cylindrical wave algorithm is more realistic than other algorithms that assume a plane wave approximation in the far field, and the measured dispersion curve phase velocity is more accurate.

[0103] The fundamental and high-order dispersion curves obtained by the new method of combined exploration of passive and active Rayleigh waves are easier to distinguish, and the frequency bands of both fundamental and high-order dispersion curves are wider, providing a solid foundation for accurate inversion of geological structures.

[0104] The embodiments of the present invention demonstrate the feasibility of the combined detection of passive and active Rayleigh surface waves from the perspective of construction conditions and calculation theory, and conduct forward-looking research for the development of the combined detection technology of passive and active Rayleigh surface waves and the introduction of relevant regulations.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A passive source and active source Rayleigh surface wave joint exploration method, characterized in that: The following steps are involved: Collecting data, including passive source data and active source data, using a uniform sampling rate of 200-300 Hz; Processing data: processing passive source data and active source data, and storing active source data of each excitation point separately; Compute the cross-correlation function and cylindrical wave dispersion.

2. The passive source and active source Rayleigh surface wave joint exploration method according to claim 1 is characterized in that: The steps of collecting data, including passive source data and active source data, uniformly using a sampling rate of 200-300 Hz, specifically include: Several instruments are deployed in the observatory array, the array is 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 stimulate the active source from the outside of one side of the observation array as a collection point, then stimulate the active source every few instruments inside the array, and finally stimulate the active source outside the other side of the observation array.

3. The passive source and active source Rayleigh surface wave joint exploration method according to claim 2 is characterized in that: The collection point continuously stimulates the active source 10-16 times, and the time interval between each stimulation is 10-12s.

4. The passive source and active source Rayleigh surface wave joint exploration method according to claim 2 is characterized in that: The step of processing the data, processing the passive source data and the active source data, and storing the active source data of each excitation point separately, specifically includes: The active source data is cut into a group of data according to each acquisition point, and the continuously excited active source signal and the passive source signal of a period of time before and after are continuously cut and saved into a data file; The observed passive source data and active source data of each acquisition point are saved as separate data files; After the array is grouped according to the detection depth, the data is called in for calculation and analysis based on the grouping situation.

5. The passive source and active source Rayleigh surface wave joint exploration method according to claim 4 is characterized in that: After the array is grouped according to the detection depth, the steps of calling in the data for calculation and analysis according to the grouping situation specifically include: calling in the passive source data and the active source data outside the group after the array is grouped, merging the passive source data and the multiple active source data called in in the order of arrangement, and then performing conventional preprocessing, grouping the data according to the duration, cross-correlation calculation and superposition to obtain the cross-correlation function.

6. The passive source and active source Rayleigh surface wave joint exploration method according to claim 5 is characterized in that: The steps of calculating the cross-correlation function and the cylindrical wave dispersion include: The cross-correlation function is given by the following formula: （1）； 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 integral, the positive branch of the cross-correlation result 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. After obtaining the empirical Green's function, the phase velocity or group velocity of the surface wave is measured from it, and the discrete expression of equation (1) in the time domain is obtained, so as to realize the cross-correlation calculation in the time domain programming, or obtain the cross-correlation result in the frequency domain through the conjugate calculation of the signal and the inverse Fourier transform; The dispersion energy is calculated using the cylindrical wave phase shift method.

7. The passive source and active source Rayleigh surface wave joint exploration method according to claim 6, characterized in that: The steps of calculating the dispersion energy using the cylindrical wave phase shift method include: The displacement record of the particle vibration excited by the point source 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. The displacement record of the particle vibration in the frequency domain at a distance r from the point source is It is expressed as: （2） In formula (2), is the spectrum of the wavelet, is the Green’s function; The circular frequency is The circular wave number at , its mathematical form is , The circular frequency is The surface wave phase velocity at ; is an imaginary unit, For and The phase angle involved; The circular frequency is The initial phase of the point source at ; Consider the distances from the point source to be and And two collinear recording points A and B, with A as the reference, the circular frequency is The cross-correlation function spectrum between the two is: （3） In formula (3), is the frequency spectrum of the cross-correlation function, symbol represents the conjugation operation; Cross-correlation removes the initial phase of the point source, so the real and imaginary parts of the cross-correlation function spectrum are used to calculate the dispersion spectrum. , the expression is: （4） In formula (4), is the touch phase, and the distance from the recording point to the virtual source and the number of test circular waves Related to; Symbol and Respectively represent the real and imaginary parts of the cross-correlation function spectrum; Test contact phase based on cylindrical wave diffusion mechanism The expression is: （5） When the touch phase and When they are completely equal, the integrand in formula (4) reaches its maximum value, and the surface wave phase velocity is picked up according to the energy peak in the dispersion spectrum image.

8. A passive source and active source Rayleigh surface wave joint exploration system, used to implement the passive source and active source Rayleigh surface wave joint exploration method as claimed in any one of claims 1 to 7, characterized in that: include: The acquisition unit is used to acquire data, wherein the data includes passive source data and active source data, and a uniform sampling rate of 200-300 Hz is used; A processing unit, used for processing data, processing passive source data and active source data, and storing active source data of each excitation point separately; The calculation unit is used to calculate the cross-correlation function and the cylindrical wave dispersion.

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