CN115685328A - High-density seismic surface wave detection method and device - Google Patents
High-density seismic surface wave detection method and device Download PDFInfo
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Abstract
The invention relates to a high-density seismic surface wave detection method and a device, wherein the method comprises the following steps: covering and acquiring signals for multiple times; arranging the seismic signals acquired along the survey line to obtain a common central point signal pair arrangement, wherein the common central point signal pair arrangement has the same central coordinates of all the signals in the common central point signal pair arrangement to the receiving point connecting line; and performing FFT positive and negative transformation on each signal pair in the arrangement of the signal pair at the common central point to obtain a time variable cross-correlation curve of each frequency of the signal pair, performing coordinate transformation on the time variable cross-correlation curve of each frequency of the signal pair according to the distance between the signal pair at the common central point to obtain a speed variable cross-correlation curve corresponding to each frequency, solving the surface wave speed according to the sum of the speed variable cross-correlation curves corresponding to all the frequencies, and solving the surface wave dispersion curve of the signal pair at the arrangement central point. The method has the advantages of convenience and rapidness in solving the dispersion curve, high precision, high density and the like, and greatly improves the detection efficiency.
Description
Technical Field
The invention relates to the technical field of seismic surface wave detection and exploration, in particular to a high-density seismic surface wave detection method and device.
Background
With the rapid development of the basic engineering construction business of China, the surface wave exploration occupies an important position in the engineering geophysical prospecting method at present. The frequency dispersion curve calculated by the measured surface wave signal can be used for directly layering the field, and the transverse wave velocity (Vs) of each layer can be further calculated, so that the method has a plurality of applications in engineering and geology. Meanwhile, the surface wave method has very loose requirements on a test field and a used instrument, and the two-channel signals from the spread arrangement of the earthquake received by the multi-channel seismograph to the signal received by the virtual instrument can be used for calculating and explaining the surface wave dispersion curve. However, the application of surface waves has many advantages, and there is a key problem in how to realize high-precision, high-density and high-efficiency surface wave detection and exploration.
Disclosure of Invention
The invention aims to provide a high-density seismic surface wave detection method and device, which are used for solving the problems in the prior art.
In a first aspect, the present invention provides a high density seismic surface wave detection method, comprising:
covering and acquiring signals for multiple times;
arranging seismic signals acquired along a survey line to obtain a common central point signal pair arrangement, wherein the central coordinates of receiving point connecting lines of all signal pairs in the common central point signal pair arrangement are the same;
and performing FFT positive and negative transformation on each signal pair in the arrangement of the common central point signal pair to obtain a time variable cross-correlation curve of each frequency of the signal pair, performing coordinate transformation on the time variable cross-correlation curve of each frequency of the signal pair according to the distance between the common central point signal pair to obtain a speed variable cross-correlation curve corresponding to each frequency, and solving the surface wave speed according to the sum of the speed variable cross-correlation curves corresponding to all the frequencies so as to solve the surface wave frequency dispersion curve of the common central point signal pair at the arranged central point.
Further, the signal acquisition by covering for multiple times is performed by using a wireless distributed seismograph, and the wireless distributed seismograph comprises a signal acquisition device, a wave detector and a computer;
the signal collector comprises 3 or more collectors, each collector is provided with 4 or more independent channels, and the computer is used as a main control platform of the wireless distributed seismograph;
the collectors are independently numbered in sequence, when each collector moves forwards, the received signals are used for automatically generating common shot point arrangement signals according to the collector numbers, common central point signal pairs are extracted and arranged according to the multiple covering common shot point signal records, the common central points are positioned at the centers of two adjacent detection points, and the point distance is equal to the track distance;
the wave detector is a broadband acceleration sensor or other sensors, an FFT band-pass filtering method is applied, low-frequency components in signals are used for surface wave detection, and high-frequency components of the signals are used for reflected wave method exploration.
Further, the two signals in each signal pair in the common midpoint signal pair arrangement have the same excitation point, and each arrangement consists of multiple signal pairs, wherein 2 or more signal pairs have different measurement point spacing.
Further, the performing FFT positive and negative transformation on each signal pair in the arrangement of signal pairs at the common center point comprises:
the frequency spectrum refinement is realized by adding zero after the signal data so as to increase the signal length, and the analysis precision is improved;
the calculation precision is improved by introducing a window function in the formula and then carrying out FFT inverse transformation on each frequency signal.
Further, the coordinate transformation of the time-variable cross-correlation curve of each frequency of the signal pair to obtain a velocity-variable cross-correlation curve corresponding to each frequency includes:
the travel time of the surface wave signal between two measuring points corresponds to a certain wave crest on the time variable cross-correlation curve, wherein when the distance between the two measuring points is less than one wave crest, the surface wave corresponds to the first wave crest, and the surface wave speed after coordinate transformation also corresponds to a certain wave crest on the speed variable cross-correlation curve corresponding to each frequency.
Further, said then calculating the velocity of the surface wave from the sum of the velocity variable cross-correlation curves corresponding to all frequencies comprises:
summing all signals of the common central point of a certain frequency with corresponding velocity variable cross-correlation curves, at a surface wave velocity point, correspondingly summing wave crests on each velocity variable cross-correlation curve to obtain a maximum value, and taking the velocity value corresponding to the maximum value on the obtained cross-correlation summation curve as a surface wave velocity;
and the velocity value corresponding to the maximum value on the cross-correlation summation curve obtained according to each frequency is also the surface wave velocity of the frequency signal, and the surface wave velocities corresponding to all the frequencies are obtained according to the sum of the velocity variable cross-correlation curves corresponding to all the frequencies.
Further, said solving a surface wave dispersion curve of the common center point signal to the arranged center point position includes:
according to the effective frequency range and the speed change interval of the surface wave signal, a plane coordinate system is established by taking a X, Y axis as the speed and the frequency respectively, a cross-correlation summation curve obtained by each frequency is drawn in a plane in sequence, and then a speed value corresponding to the maximum value on the cross-correlation summation curve is connected in sequence from small to large according to the frequency change to obtain a frequency and speed change curve, namely a surface wave frequency dispersion curve of the common central point signal to the arranged central point.
Or, the cross-correlation summation curve value obtained by each frequency drawn in the plan view is represented by different colors, the color is darker as the numerical value is larger, a surface wave cross-correlation summation curve chromatogram is obtained, and a surface wave frequency and speed change curve, namely a surface wave dispersion curve of the center point position of the common center point signal pair arrangement, is obtained in the surface wave cross-correlation summation curve chromatogram according to the connection line of each frequency and the speed point corresponding to the deepest color.
In a second aspect, the present invention provides a high density seismic surface wave detection apparatus comprising:
the signal acquisition module is used for carrying out covering acquisition signals for multiple times;
the signal arranging module is used for arranging the seismic signals acquired along the survey line to obtain a common central point signal pair arrangement, and the central coordinates of the receiving point connecting lines of all signal pairs in the common central point signal pair arrangement are the same;
and the surface wave solving module is used for performing FFT positive and negative transformation on each signal pair in the arrangement of the common central point signal pair to obtain a time variable cross-correlation curve of each frequency of the signal pair, performing coordinate transformation on the time variable cross-correlation curve of each frequency of the signal pair according to the distance between the common central point signal pair to obtain a speed variable cross-correlation curve corresponding to each frequency, and solving the surface wave speed according to the sum of the speed variable cross-correlation curves corresponding to all the frequencies so as to solve the surface wave frequency dispersion curve of the common central point signal pair at the arranged central point.
According to the technical scheme, the high-density seismic surface wave detection method and the high-density seismic surface wave detection device provided by the invention have the advantages that the very dense common central point signal pair arrangement is acquired, the number of the signals of each common central point is far larger than that of the signals of the common shot point arrangement, and each common central point signal pair arrangement can solve a high-precision surface wave frequency dispersion curve. The method has the advantages of convenience and rapidness in solving the dispersion curve, high precision, high density distribution and the like, and greatly improves the detection efficiency.
Drawings
In order to more clearly illustrate the embodiments or technical solutions of the present invention, the drawings used in the embodiments or technical solutions in the prior art are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a flow chart of a high density seismic surface wave detection method according to an embodiment of the invention;
FIG. 2 is a schematic diagram of the operation of 1 collector (4 channels) according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of 3 collectors (12 channels) and a conventional surface wave according to an embodiment of the invention;
FIG. 4 is a schematic diagram of a high-density surface wave of 3 collectors (12 channels) according to an embodiment of the invention;
FIG. 5 is a schematic diagram of collecting CMC signals in accordance with an embodiment of the present invention;
FIG. 6 is a flow chart of a measured CMC signal calculation dispersion curve in accordance with an embodiment of the present invention;
FIG. 7 is a schematic structural diagram of a high density seismic surface wave detection device according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
During the propagation of seismic waves in the subsurface, excited by a heavy hammer or other means, along this particular free surface of the earth, a particular but common wave, called a "rayleigh surface wave" or "ground roll wave", usually called a "surface wave", is generated, which exists only in the surface layer, due to the interference of the P-wave and the SV-wave. In the process of outward propagation of Rayleigh surface waves from a seismic source, the vibration of surface wave particles simultaneously has a vertical direction component and a horizontal direction component, and the track of the vibration is an ellipse rotating anticlockwise on the ground surface. When a low-speed covering layer or a laminated medium exists on the earth surface, the surface waves have a dispersion phenomenon, namely, the speed of the surface waves changes along with the frequency. The wave velocity curves corresponding to different frequency signals are called dispersion curves, and the calculation of the dispersion curves is an important component of surface wave exploration. In the surface wave exploration process, 1/2 wavelength of a signal is generally used as a detection depth, and a surface wave frequency dispersion curve (f-V) is calculated according to a wavelength calculation formula (lambda = V/f) R ) Can be converted into a depth wave velocity change curve (H-V) required by engineering R )。
The early two-channel phase difference method has the characteristics of simplicity and convenience in implementation, the number of required detectors is small, and the folded phase (phi =2n pi + delta phi) needs to be unfolded and calculated when the phase difference is calculated. When the folding phase is unfolded and calculated, the n value in the formula cannot be directly calculated and determined, and the obtained n value and the obtained speed need to be judged according to experience, so that certain limitations exist.
At present, the most commonly used dispersion curve calculation methods comprise methods (based on common shot point multi-channel arrangement signals) such as F-K and tau-P, the problem that a phase difference method cannot solve the problem of folding phase difference is solved, and the method is widely used in engineering. However, due to the limitation of the method (instruments are generally not less than 12 channels), in the signal acquisition process, only one dispersion curve can be calculated and extracted from each common shot point spread arrangement signal record, the working efficiency is directly influenced, on the other hand, each solved dispersion curve is the average reflection of the arrangement area, and the curve positioning accuracy is poor.
According to the analysis, the surface wave detection plays an important role in engineering geological exploration and in-situ test, and on the other hand, due to the limitation of the currently and commonly used method, the working efficiency and the achievement precision are directly influenced.
The invention provides a high-density seismic surface wave detection method and device, which can quickly acquire a high-precision surface wave frequency dispersion curve and realize high-density surface wave detection and exploration.
Fig. 1 is a flowchart of a high-density seismic surface wave detection method according to an embodiment of the present invention, and referring to fig. 1, the high-density seismic surface wave detection method provided by the embodiment of the present invention includes:
In the embodiment of the present invention, it should be noted that the scheme provided by the present invention includes:
s1, as shown in figure 2, a wireless distributed seismograph is used for covering and acquiring signals for multiple times, an instrument system is composed of a plurality of collectors, and each collector is provided with 4 independent channels (or a plurality of channels);
s2, arranging seismic signals acquired along a survey line to obtain a common central point signal pair arrangement (CMC), wherein all signals in the CMC arrangement have to be the same as the central coordinates (point positions) of a receiving point connecting line;
s3, performing FFT positive and negative transformation on each signal pair (i) in the CMC arrangement to obtain each frequency (f) of the signal k ) Time variable cross correlation curve
Then according to the distance between CMC signal pairs, the time variable cross-correlation curve is subjected to coordinate transformation to obtain the speed variable cross-correlation curve corresponding to each frequency
Then according to
Directly determining each frequency (f) k ) Corresponding surface wave velocity V R Further, the surface wave dispersion curve (f-V) of the CMC central point position can be solved R )。
The signal collector has a Wi-Fi wireless data transmission function, and has higher efficiency compared with a conventional wired connection multi-covering working method, as shown in fig. 3, the multi-covering signal collection is carried out by selecting multiple collectors, the collector at the rearmost side of the survey line is moved to the foremost side of the arrangement after the unilateral or bilateral excitation signal collection is completed, and the moving step distance is the product of the number of the collector channels and the track distance (dx). When the array is moved once, a conventional surface wave method takes the array center as a measuring point to calculate a frequency dispersion curve, and the distance between the measuring points of the frequency dispersion curve is the moving step distance. If the collector (4 channels) is moved by 1 time, the distance between the measuring points of the dispersion curve is 4dx, and if the collector is moved by 2 times, the distance between the measuring points is 8dx.
The signal pairs (CMC) are arranged, and the two signals in each signal pair must be the same excitation point (namely, common shot point signals); the coordinates of the centers of all the signals in the array (point locations) must be the same for their reception points, but their excitation points may be different. As shown in fig. 4, two adjacent centers of the detection points are sequentially taken as CMC arrangement centers Xc on the measurement line, then CMC signals of all symbols and conditions are generated into a file, and a dispersion curve at the measurement point Xc (that is, xc is a surface wave measurement point) can be calculated according to the file, and the distance between the measurement points of the dispersion curve is track pitch (dx) and is irrelevant to the moving step pitch.
If 1 collector (4 channels) is moved each time, the density of the measurement points of the dispersion curve is 4 times that of the conventional method, and if 2 collectors are moved each time, the density of the measurement points of the dispersion curve is 8 times that of the conventional method. On the other hand, any surface wave measuring point (j) on the measuring line is selected, and the concentric point signal pairs of the measuring point comprise 20 signals (10 signal pairs) of 2 signals in the first arrangement, 6 signals in the second arrangement and 2 signals in the third arrangement. The number of the signals participating in the calculation is far larger than that of the signals in the conventional method (12 common shot point arrangement signals) except for individual measuring points at two ends of a measuring line, so that the calculation precision of the surface wave dispersion curve can be effectively improved.
The CMC signal is subjected to FFT forward and backward transformation, and as shown in fig. 5, x11/x12 is any common center signal pair in the CMC arrangement. The measured signal is synthesized by a plurality of frequency signals according to the principle of vibration, and the various frequency signals contained in the measured signal can be separated by using FFT (fast Fourier transform), and the mathematical expression of the measured signal is as follows:
X 11 (f)＝∫x 11 (t)e -2π·jft dt；X 12 (f)＝∫x 12 (t)e -2π·jft dt (1)
if for one of the frequency signals (f) k ) And performing inverse FFT (fast Fourier transform) after conjugate multiplication, wherein the obtained result is a time variable cross-correlation curve corresponding to the frequency signals on the two measuring points, and the mathematical expression of the curve is as follows:
in the specific implementation process, a frequency spectrum thinning technology is applied, and a window function W (f) is introduced into the formula k ) That is, assuming that the window width is 2w and the simplest expression is, when (f) k -w≤f k ≤f k W (f) at + W k ) The other is zero =1, and more preferable effects can be obtained.
On the other hand, for the x11/x12 point, a certain frequency signal (f) is present k ) The wave equation can be expressed as:
according to the above formulas (3) and (4), the cross-correlation curve calculation formula is as follows:
the above equation (6) shows that two periodic signals with zero mean and the same frequency retain the information of the circular frequencies and their phase differences in the cross-correlation function, and when τ = Δ t 1 ± nT (n =0, 1, 2, …, when n =0, τ = Δ t 1 ＝τ R ) In a
The maximum value is on the curve, and the mathematical expression is as follows:
from the above equation (7), it can be seen that the surface wave signal travels between two measuring points R Corresponding to a certain peak on the cross-correlation curve of the time variable, when the distance between two measuring points is less than the wavelength of the signal, tau R Corresponding to the first peak on the curve. When the distance between two measuring points is greater than the signal wavelength, tau R Since the wave velocity and the wavelength of the surface wave signal are unknown (required to be obtained) for any subsequent peak, the signal travel time cannot be directly obtained from the time-dependent cross-correlation curve.
Said cross correlation curve with time variation
Performing coordinate transformation (i.e. a certain frequency signal f in the ith signal pair) k ) Let the distance between two measuring points be Δ X i Application of
Cross correlation curve for time variable
Coordinate transformation is carried out to obtain a speed variable cross-correlation curve
Similarly, if a certain measuring point surface wave CMC is arranged with N common central point signal pairs, N velocity variable cross-correlation curves can be calculated by the method
From the above analysis, it can be seen that the surface wave signal travels between the two measuring points R Corresponding to a certain peak on the correlation curve, so that after coordinate transformation, the surface wave velocity
Same as
One on the curveThe wave crests correspond.
Said is according to
Direct determination of surface wave velocity V R I.e. first applying the formula
And performing superposition summation on the N velocity variable cross-correlation curves. Since when V = V R At each strip
There is a maximum on the curve. Therefore, after the multiple curves are added and combined, the surface wave velocity V is obtained R The maximum value of the curve is superposed and added, and still corresponds to the maximum value on the R (v) curve, i.e. a certain frequency signal f can be directly obtained according to the maximum value on the R (v) curve k Corresponding surface wave velocity V R . Similarly, the surface wave velocities corresponding to all different frequencies in the effective frequency band of the CMC signal can be further solved, and the surface wave dispersion curve (f-V) of the CMC central point position can be solved according to the surface wave velocities R ) (ii) a Meanwhile, a chromatographic image can be drawn according to the signal frequency and the speed scanning interval, and a surface wave frequency dispersion curve can be more intuitively solved through the chromatographic image.
The above discussion is under the assumption that f k The method is carried out under the condition that the signal is a surface wave signal, the frequency spectrum of the actually measured signal possibly contains various wave components, and the problem can be well solved according to the characteristics of the surface wave. Firstly, according to the effective frequency and the speed change range of the surface wave, the influence of noise and longitudinal wave signals can be effectively overcome by properly selecting the scanning frequency and the scanning wave speed interval. The difference between the transverse wave and the surface wave is small, so that the difference cannot be eliminated by selecting the wave velocity scanning interval, but the transverse wave energy is smaller than the surface wave energy, so that the transverse wave energy can be ignored. By appropriate selection of the scanning frequency (f) k ) The window width is wide, the obtained related energy curve R (V) is normalized, weak signals can be enhanced, and a surface wave frequency dispersion curve (f-V) can be more effectively obtained R )。
Specifically, as shown in FIG. 6.a, there are 3 CMC arraysAnd the signal pairs share the central point, wherein the central point Xc =10.5m, and the coordinates of the measuring points of the 3 signal pairs are respectively 10/11, 9.5/11.5 and 7.5/13.5. After performing FFT forward and backward transformation and coordinate transformation on each signal pair in the CMC arrangement, a chromatogram image can be drawn according to the velocity variable cross-correlation summation curve R (v) corresponding to all different frequencies within the effective frequency band of the signal, as shown in fig. 6.b. In the figure, the abscissa represents signal power spectrum and wave velocity scanning interval, the ordinate represents frequency scanning interval, the color of the chromatographic image is determined according to an R (V) curve (the color is darker when the numerical value is larger in the figure), and the wave velocity V is caused by the surface R Corresponding to the maximum value of the curve, so that the scanning wave velocity corresponding to the darkest color in the image is the surface wave velocity V R According to V corresponding to all scanning frequencies in the chromatogram R Then, the surface wave dispersion curve (f-V) can be solved (extracted) R ). As shown in FIG. 6.c, the surface wave dispersion curve (f-V) is based on the surface wave half-wavelength detection principle R ) Can be converted into a depth wave velocity change curve (H-V) required by engineering R )。
Fig. 7 is a schematic diagram of a high-density seismic surface wave detection device according to an embodiment of the present invention, and as shown in fig. 7, the high-density seismic surface wave detection device according to the embodiment of the present invention includes:
a signal acquisition module 710, configured to perform multiple coverage signal acquisition;
the signal arranging module 720 is used for arranging the seismic signals acquired along the survey line to obtain a common central point signal pair arrangement, wherein the coordinates of the centers of the connecting lines of the receiving points of all the signals in the common central point signal pair arrangement are the same;
the surface wave solving module 730 is configured to perform FFT forward and backward transformation on each signal pair in the arrangement of the common center point signal pair to obtain a time variable cross-correlation curve of each frequency of the signal pair, perform coordinate transformation on the time variable cross-correlation curve of each frequency of the signal pair according to a distance between the common center point signal pair to obtain a velocity variable cross-correlation curve corresponding to each frequency, and then solve a surface wave velocity according to a sum of the velocity variable cross-correlation curves corresponding to all frequencies, thereby solving a surface wave dispersion curve of the common center point signal pair at the arranged center point.
The high-density seismic surface wave detection device provided by the embodiment of the invention can be used for executing the high-density seismic surface wave detection method in the embodiment, and the working principle and the beneficial effect are similar, so detailed description is omitted here, and specific contents can be referred to the introduction of the embodiment.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (8)
1. A high-density seismic surface wave detection method is characterized by comprising the following steps:
covering and acquiring signals for multiple times;
arranging seismic signals acquired along a survey line to obtain a common central point signal pair arrangement, wherein the central coordinates of receiving point connecting lines of all signal pairs in the common central point signal pair arrangement are the same;
and performing FFT positive and negative transformation on each signal pair in the arrangement of the common central point signal pair to obtain a time variable cross-correlation curve of each frequency of the signal pair, performing coordinate transformation on the time variable cross-correlation curve of each frequency of the signal pair according to the distance between the common central point signal pair to obtain a speed variable cross-correlation curve corresponding to each frequency, and solving the surface wave speed according to the sum of the speed variable cross-correlation curves corresponding to all the frequencies so as to solve the surface wave frequency dispersion curve of the common central point signal pair at the arranged central point.
2. The method for detecting high-density seismic surface waves according to claim 1, wherein the performing of the signal acquisition for multiple coverage is performed by using a wireless distributed seismograph, and the wireless distributed seismograph comprises a signal acquisition device, a geophone and a computer;
the signal collector comprises 3 or more collectors, each collector is provided with 4 or more independent channels, and the computer is used as a main control platform of the wireless distributed seismograph;
the collectors are independently numbered in sequence, when each collector moves forwards, the received signals are used for automatically generating common shot point arrangement signals according to the collector numbers, common central point signal pairs are extracted and arranged according to the multiple covering common shot point signal records, the common central points are positioned at the centers of two adjacent detection points, and the point distance is equal to the track distance;
the detector is a broadband acceleration sensor or other sensors, an FFT band-pass filtering method is applied, medium and low frequency components of signals are used for surface wave detection, and high frequency components of the signals are used for reflected wave method exploration.
3. The method of claim 1, wherein the two signals in each of the signal pairs in the common midpoint signal pair arrangement have the same excitation point, and wherein each arrangement consists of a plurality of signal pairs, and wherein 2 or more of the signal pairs have different point spacings.
4. The method of claim 1, wherein the performing a positive-negative FFT transformation on each signal pair in the arrangement of common midpoint signal pairs comprises:
the frequency spectrum refinement is realized by adding zero after the signal data so as to increase the signal length, and the analysis precision is improved;
the calculation precision is improved by introducing a window function in the formula and then performing FFT inverse transformation on each frequency signal.
5. The method of claim 1, wherein the step of performing coordinate transformation on the time-variant cross-correlation curve of each frequency of the signal pair to obtain a velocity-variant cross-correlation curve corresponding to each frequency comprises:
the travel time of the surface wave signal between two measuring points corresponds to a certain wave crest on the time variable cross-correlation curve, wherein when the distance between the two measuring points is less than one wave crest, the surface wave corresponds to the first wave crest, and the surface wave speed after coordinate transformation also corresponds to a certain wave crest on the speed variable cross-correlation curve corresponding to each frequency.
6.A method of high density seismic surface wave detection as claimed in claim 1 wherein said then deriving the surface wave velocity from the sum of velocity variable cross-correlation curves for all frequencies comprises:
summing all signals of the common central point of a certain frequency with corresponding velocity variable cross-correlation curves, at a surface wave velocity point, correspondingly summing wave crests on each velocity variable cross-correlation curve to obtain a maximum value, and taking the velocity value corresponding to the maximum value on the obtained cross-correlation summation curve as a surface wave velocity;
and the velocity value corresponding to the maximum value on the cross-correlation summation curve obtained according to each frequency is also the surface wave velocity of the frequency signal, and the surface wave velocities corresponding to all the frequencies are obtained according to the sum of the velocity variable cross-correlation curves corresponding to all the frequencies.
7. The method of claim 1, wherein said deriving a surface wave dispersion curve of the common midpoint signal versus the aligned midpoint location comprises:
according to the effective frequency range and the speed change interval of the surface wave signal, a plane coordinate system is established by taking a X, Y axis as the speed and the frequency respectively, a cross-correlation summation curve obtained by each frequency is drawn in a plane in sequence, and then a speed value corresponding to the maximum value on the cross-correlation summation curve is connected in sequence from small to large according to the frequency change to obtain a frequency and speed change curve, namely a surface wave frequency dispersion curve of the common central point signal to the arranged central point.
Or, the cross-correlation summation curve value obtained by each frequency drawn in the plan view is represented by different colors, the color is darker as the numerical value is larger, a surface wave cross-correlation summation curve chromatogram is obtained, and a surface wave frequency and speed change curve, namely a surface wave dispersion curve of the center point position of the common center point signal pair arrangement, is obtained in the surface wave cross-correlation summation curve chromatogram according to the connection line of each frequency and the speed point corresponding to the deepest color.
8. A high density seismic surface wave detection device, comprising:
the signal acquisition module is used for carrying out covering acquisition signals for multiple times;
the signal arranging module is used for arranging the seismic signals acquired along the survey line to obtain a common central point signal pair arrangement, and the central coordinates of the receiving point connecting lines of all signal pairs in the common central point signal pair arrangement are the same;
and the surface wave solving module is used for performing FFT positive and negative transformation on each signal pair in the arrangement of the signal pair with the common central point to obtain a time variable cross-correlation curve of each frequency of the signal pair, then performing coordinate transformation on the time variable cross-correlation curve of each frequency of the signal pair according to the distance between the signal pair with the common central point to obtain a speed variable cross-correlation curve corresponding to each frequency, and then solving the surface wave speed according to the sum of the speed variable cross-correlation curves corresponding to all the frequencies so as to solve the surface wave dispersion curve of the central point position of the signal pair with the common central point.
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