CN106338766A - Pre-stack time migration method based on split-step Fourier algorithm - Google Patents

Abstract

The invention provides a Pre-stack time migration method based on a split-step Fourier algorithm. The method comprises the steps of inputting pre-processed seismic data; picking up the root mean square speed in an interactive mode; calculating the ray propagation time from an imaging point to a focus point; converting seismic data of a time-space domain into frequency-wave number; acquiring a continuation value of a background wave field; transforming the continued wave field into the frequency-space domain through Fourier transform, and performing a time shift operation through a split-step Fourier time shift operator of the time domain so as to realize continuation for a disturbance wave field; and performing phase shift on a frequency-space domain seismic wave field and carrying out integration on the effective frequency band by using a excitation time imaging condition so as to acquire a seismic imaging result of a shot record. The pre-stack time migration method based on the split-step Fourier algorithm can carry out migration by applying the root mean square speed, and improves the adaptive capacity for speed vertical and longitudinal variations and the amplitude preserving capacity for migration imaging of pre-stack time migration under the condition of not increasing the speed modeling difficulty.

Description

Prestack time migration method based on split-step fast fourier transformation

Technical field

The present invention relates to the migration imaging field in seism processing, especially relate to a kind of being based on and divide The prestack time migration method of step Fourier algorithm.

Background technology

Seismic migration is a kind of complementary operation that earthquake information enters rearrangement, to make seismic wave energy return Position, to the actual position in its space, obtains underground real construction form.Wave equation prestack migration imaging master It is divided into pre-stack time migration imaging and pre-stack depth migration imaging two class.Pre-stack depth migration is to underground speed Degree cross directional variations strong adaptability, it is possible to provide the photo-quality imaging result of Depth Domain, but its essence to rate pattern Degree has high demands and computationally intensive, therefore, is the scheme of a high investment high repayment.Pre-stack time migration becomes As computational efficiency is high, its requirement to rate pattern application conditions is low simultaneously, horizontal in construction complexity, speed There is preferable imaging effect in the case of change less.Therefore, pre-stack time migration is reality at this stage Use technology.

Pre-stack time migration imaging can be divided into two big class according to the principle that algorithm is realized: based on ray theory Offset method and the offset method based on wave field extrapolation.Conventional ray method pre-stack time migration adopts mean square Root speed, it is capable of vertically and horizontally speed change, and amount of calculation is less, and calculates root mean sequare velocity and improve Its precision comparison is easy, but its numerical value response characteristic is not so good as wave field method.Even so, current main flow In seismic data processing software, pre-stack time migration (pstm) still only has ray method without wave field method.This It is because that wave field method pstm quotes interval velocity in recursive process, during calculating, m- interval velocity model has very Big difficulty.Therefore, in practice, if spending equal cost if necessary, people would rather set up depth - interval velocity model the higher pre-stack depth migration of choice accuracy, so, quoting interval velocity model becomes The biggest obstacle of wave field method pstm.

With the increase of oil-gas exploration difficulty, it is more and more important that seismic data protects width process.Go out in recent years Show plane wave, phase shift adds interpolation and the wave field class prestack time migration technique such as constant-velocity scan, but it is all Multi objective cannot meet real requirement.

In frequency wavenumber domain, dubrulle (1983), ekren and ursin (1999) achieve to common big gun Inspection away from plane wave wave field extrapolation.But, common offset road collection plane wave pre-stack time migration in theory Can process has vertical velocity change medium, and for Seismic Wave Dynamics Characteristics holding also need into One step improves.

Integral formula (ehinger a., lailly p., and marfurt k.j. from single track Green's function 1996) set out, jianhua p. and dan n. (2008) borrows phase shift method and obtains responding spy with wave field method The kirchhoff type pre-stack time migration result of property.This mode can retain the major advantage of ray method, Amplitude and waveform characteristic can also be improved.But, carried out in units of road wave field extrapolation can lead to considerable Amount of calculation.

Wang Youxin (2008) realizes the pre-stack time migration to single shot record by the method that phase shift adds interpolation. The method imaging angle is high, but computationally intensive, calculates wave field by linear interpolation it is impossible to adapt to laterally The large change of speed.

Sergey fomel (2013) proposes wave equation goes to from cartesian coordinate system imaging ray seat The method being solved under mark system, The method avoids in Conventional Time skew to Green's function calculating Approximate solution, improves time migration computational accuracy, but its cross directional variations bad adaptability to speed.

Because wave field method has good numerical characteristic, so, wave field method pre-stack time migration has important Practical value, many research work attempt to the estimated performance of wave field method, but are limited by and quote all Root speed and speed-adaptive change two problems it is difficult to meet real requirement.We have invented one for this Plant the new prestack time migration method based on split-step fast fourier transformation, solve this two technical problems.

Content of the invention

It is an object of the invention to provide a kind of can produce more true and reliable imaging results based on point The prestack time migration method of step Fourier algorithm.

The purpose of the present invention can be achieved by the following technical measures: the prestack based on split-step fast fourier transformation Time migration method, should be included based on the prestack time migration method of split-step fast fourier transformation: step 1, Input pretreated geological data p_u(t,x,y)；Step 2, using pretreated geological data p_u(t, x, y) is calculated root mean sequare velocity spectrum, picks up root mean sequare velocity by interactive mode, and obtains work Mean-square-root velocity field v in the range of area_rms(t,x,y)；Step 3, based on mean-square-root velocity field v_rms(t, x, y), meter It is counted as picture point to the ray propagation time τ of focal point；Step 4, using Fourier transformation, by when m- sky Between domain geological data p_u(t, x, y) transforms to frequency wavenumber domain p^* _u(w,k_x,k_y), wherein, p^* _u(w,k_x,k_y)=fft (p_u(t,x,y))；Step 5, using step Fourier phase-shift operator by p^* _u(w,k_x,k_y) straight Connect continuation to the time τ of underground imaging point, obtain the continuation value of background wave field；Step 6, by continuation Wave field afterwards is fourier transformed Frequency-Space Domain, by the step Fourier time-displacement operator of time domain Carry out time shift computing, realize the continuation to disturbance wave field；And step 7, according to imaging point to focal point Ray propagation time τ, using firing time image-forming condition, phase place is made to Frequency-Space Domain seismic wave field Move and carry out the integration of effective frequency range, obtain the seismic imaging result of big gun record.

The purpose of the present invention also can be achieved by the following technical measures:

In step 1, interval velocity model in depth domain is just being drilled with the common big gun collection p obtaining_u(t, x, y) carry out denoising, These conventional pretreatment of static correction.

In step 2, pick up the root mean sequare velocity of seed point location by interactive mode, insert through three-dimensional The smooth mean-square-root velocity field v obtaining target area of value_rms(t, x, y), described mean-square-root velocity field is used for earthquake The step Fourier pre-stack time migration of data.

In step 2, using pretreated geological data p_u(t, x, y) calculates root mean sequare velocity spectrum, passes through Interactive mode, picks up the root mean sequare velocity of seed point location at equal intervals according to 100 meters, then passes through interpolation Smooth acquisition is spaced apart the time domain mean-square-root velocity field v of 10 meters of model_rms(t, x, y), that is, prestack time is inclined Move required velocity field.

In step 3, based on mean-square-root velocity field v_rms(t, x, y), calculates imaging point using ray method and arrives The ray propagation time of focal pointWherein, τ is the time of imaging point, and x is The position of imaging point, x_sFor the position of focal point, v_rmsFor root mean sequare velocity.

In steps of 5, by the mean-square-root velocity field in application time domain, obtained by single step continuation, The mutually transposition of background velocity is directed on continuation time τ, described phase-shift operator expression formula is as follows:

${p^{*}}_u(w,k_x,k_y,\mathrm{\τ})={p^{*}}_u(w,k_x,k_y,0)\·e^{i\mathrm{\τ}\sqrt{w^2{s^2}_{rms0}\left(\mathrm{\τ}\right)-k_x^2-k_y^2}}$

Wherein, v_rms0(τ) for the background root-mean-square field speed angle value in τ moment, s_rms0(τ) for the slowness of ambient field, And s_rms0(τ)=1/v_rms0(τ), w is frequency, k_xFor the wave number in x direction, k_yWave number for y direction.

In step 6, calculated for step 5 wave field is transformed into frequency-space through Fourier inversion Domain, on this basis by the step Fourier time-displacement operator of time domain be calculated for Perturbation when Transposition, applies time-displacement operator, realizes the continuation to Perturbation, its expression formula is:

$p{{\_}^{*}}_u(w,x,y,\mathrm{\τ})={p^{*}}_u(w,x,y,\mathrm{\τ})\·e^{{\mathrm{iw\δs}}_{rms}(\mathrm{\τ},x,y)}$

Wherein, δ s_rms(τ, x, y) is the slowness of Perturbation, so far, completes the earthquake of geophone station side is remembered The wave field extrapolation in record τ moment at imaging point position.

In step 7, Frequency-Space Domain seismic wave field continuation value step 6 being obtained, during according to exciting Between image-forming condition implementing phase mobile and effective frequency range is integrated, obtain final temporal-spatial field Seismic wave field value, its image-forming condition expression formula is:

$i(x,y,t_s)={\left(\frac{1}{2\mathrm{\π}}\right)}^2{\&integral;}_{w1}^{w2}i(x,y,\mathrm{\τ},w)e^{iw(\mathrm{\τ}-t_s)}dw$

Wherein, i is the temporal-spatial field seismic wave field after phase shift, w1 to w2 having for seismic wave Effect frequency band range.

Step 7 also includes: record-shifted for big gun imaging is converted into common imaging gather, merges identical big gun inspection Away from；All single-shot imaging results are superimposed according to locus, or the direct superposition to common imaging gather, Obtain the pre-stack time migration imaging results of target area.

The present invention proposes a kind of prestack time migration method based on split-step fast fourier transformation, key therein It is that wave field extrapolation is realized according to root mean sequare velocity.Generally, ray method quotes root mean sequare velocity, and wave field method is drawn With interval velocity, and set up interval velocity model and have great difficulty, so, pre-stack time migration is mainly using penetrating Collimation method.However, the numerical value response characteristic of ray method pre-stack time migration is not so good as wave field method and guarantor's width is poor, For this reason, it is pre-stack time migration needs that the application root mean sequare velocity being capable of simple and fast realizes the skew of wave field method The major issue solving.In wave field class algorithm, phase shift method, plane wave method, step Fourier and Screen algorithm can become progressively recursion into One-step Extrapolation, thus quoting root mean sequare velocity, wherein step Fourier Algorithm is succinct and has single order lateral velocity variation ability, just meets the precondition of pre-stack time migration.This Invention is based on split-step fast fourier transformation, and application root mean sequare velocity achieves wave field method pre-stack time migration, its It is mainly characterized by: 1. quote root mean sequare velocity, speed is realized by single step wave field extrapolation longitudinally varying, keep away Exempt from the error that interval velocity introduces in successively recursion downwards；2. compensated by relative time shift and realize laterally speed Degree single order change；3. pass through the mixing of shot point ray method and geophone station wave field method, realize ray method high efficiency Mutual supplement with each other's advantages with wave field method high-fidelity.Either ray method or wave field method, both can use in theory In pre-stack time migration it is also possible to be used for pre-stack depth migration.In practice, if it is known that interval velocity, fold Front depth migration is better than the imaging effect of pre-stack time migration, but, due to calculating accurate interval velocity ratio Calculate root mean sequare velocity difficult, therefore, wave field method pre-stack time migration is realized not using mean-square-root velocity field Lose as the high imaging method of a kind of efficient quick, fidelity.

The prestack time migration method based on split-step fast fourier transformation of the present invention, wave field method prestack time is inclined Before moving technology application, first the pretreatment such as conventional denoising, static correction are carried out to geological data, by analysis Geological data, obtains accurate mean-square-root velocity field.Then, using ray method, calculate focal point to becoming The raytime of picture point.Now, geological data is transformed into frequency wavenumber domain, using background root-mean-square The geological data of velocity on frequency-wave-number domain carries out a phase shift, realizes the wave field extrapolation to ambient field； Geological data after continuation is transformed to Frequency-Space Domain, is carried out once using disturbance mean-square-root velocity field Time shift, realizes the wave field extrapolation to Perturbation；According to the propagation time of focal point to imaging point, to continuation Frequency-Space Domain wave field implementing phase afterwards moves；After moving through wavefield phase, to seismic wavefield data Carry out the integration of effective frequency range, obtain final seismic wave field continuation value；Finally, all single-shots are imaged Result is superimposed according to locus, or the direct superposition to common imaging gather, obtains the prestack of target area Time migration imaging results.

Inexpensive root mean sequare velocity should be adopted by prestack time migration method based on split-step fast fourier transformation Field achieves the pre-stack time migration based on split-step fast fourier transformation, avoids layer by single step wave field extrapolation Speed repeats constantly positive inverse transformation in downward recursion, improves skew while not increasing and calculate cost Precision simultaneously improves amplitude response.Meanwhile, by the hybrid operation of ray method and wave field method, both embodied The good amplitude response of wave field method also adopts the advantage of ray method speed-adaptive change in time and space, takes The effect that must have complementary advantages, is greatly improved computational efficiency.Compared with conventional pre-stack time migration algorithm, The present invention can apply root mean sequare velocity to enter line displacement, in the case of the modeling difficulty that do not gather way, carries Adaptability and the guarantor's width ability to migration imaging that high pre-stack time migration vertically and horizontally changes to speed.

Brief description

Fig. 1 is the specific embodiment of the prestack time migration method based on split-step fast fourier transformation of the present invention Flow chart；

Fig. 2 is the corresponding depth of marmousi model-interval velocity schematic diagram in the specific embodiment of the present invention；

Fig. 3 be the present invention specific embodiment in marmousi model corresponding when m- root mean sequare velocity show It is intended to；

Fig. 4 is the ray method pre-stack time migration result of marmousi model in the specific embodiment of the present invention Schematic diagram；

Fig. 5 is the ripple based on split-step fast fourier transformation of marmousi model in the specific embodiment of the present invention Field method pre-stack time migration result schematic diagram；

Specific embodiment

Purpose, technical scheme and advantage for enabling the embodiment of the present invention become apparent, below in conjunction with Accompanying drawing in the embodiment of the present invention, carries out clear, complete retouching to the technical scheme in the embodiment of the present invention State.

As shown in figure 1, Fig. 1 is the prestack time migration method based on split-step fast fourier transformation of the present invention Flow chart.

In step 101, input geological data, this geological data is pre- through conventional denoising, static correction etc. The common-shot-gather processing.In one embodiment, to marmousi Depth Domain interval velocity as shown in Figure 2 The common big gun collection p that forward modeling obtains_u(t, x, y) carries out the routine pretreatment such as denoising, static correction.Flow process enters To step 102.

In step 102, pick up root mean sequare velocity, be calculated using pretreated geological data mean square Root normal-moveout spectrum, picks up the root mean sequare velocity of seed point location by interactive mode, smooths through three-dimensional interpolation Obtain the mean-square-root velocity field of target area, described mean-square-root velocity field is used in substep Fu of geological data Leaf pre-stack time migration.In one embodiment, using pretreated geological data p_u(t, x, y) calculates all Root normal-moveout spectrum, by interactive mode, the root-mean-square picking up seed point location according to 100 meters at equal intervals is fast Degree, then obtains the time of the as shown in Figure 3 marmousi model being spaced apart 10 meters by interpolation smoothing Domain mean-square-root velocity field v_rms(t, x, y), i.e. velocity field needed for pre-stack time migration.Flow process enters into step 103.

In step 103, when being travelled using ray computational methods and adopt described mean-square-root velocity field, calculate Imaging point is to the ray propagation time of focal point.In one embodiment, based on mean-square-root velocity field v_rms(t, x, y), calculates imaging point to the ray propagation time of focal point using ray methodWherein, τ is the time of imaging point, and x is the position of imaging point, x_sFor shake The position of source point, v_rmsFor root mean sequare velocity, flow process enters into step 104.

In step 104, using Fourier transformation, the common-shot-gather of temporal-spatial field is transformed to frequency - wave-number domain.In one embodiment, changed by two-dimentional Fourier, by the geophone station side through pretreatment Geological data is changed into the p of frequency wavenumber domain^* _u(w,k_x,k_y), wherein p^* _u(w,k_x,k_y)=fft (p_u(t,x,y)). Flow process enters into step 105.

In step 105, using step Fourier phase-shift operator and using described mean-square-root velocity field to described Common-shot-gather geological data carries out wave field extrapolation, obtains the outer frequency wavenumber domain seismic wave number of fields postponing According to.

To earthquake market demand one by reference background slowness s_rms0(τ) phase-shift operator obtaining.Deep in prestack In degree skew, the step-length of phase shift continuation is a fixing depth value δ z, needs to obtain into by Layer by layer recurrence The wave field extrapolation value of image point position.In embodiments of the present invention, by the root mean sequare velocity in application time domain , obtained by single step continuation, the mutually transposition of background velocity, described phase shift are directed on continuation time τ Operator expression formula is as follows:

$p{*}_u(w,k_x,k_y,\mathrm{\τ})=p{*}_u(w,k_x,k_y,0).e^{i\mathrm{\τ}\sqrt{w^2{s^2}_{\mathrm{rms}0}\left(\mathrm{\τ}\right)-k_x^2-k_y^2}}$

Wherein, v_rms0(τ) for the background root-mean-square field speed angle value in τ moment, s_rms0(τ) for the slowness of ambient field, And s_rms0(τ)=1/v_rms0(τ), w is frequency, k_xFor the wave number in x direction, k_yWave number for y direction.

Application above-mentioned formula is it is possible to by upgoing wave p^* _u(w,k_x,k_y) directly continuation is to underground imaging point On time τ, obtain the continuation value of background wave field.Flow process enters into step 106.

In step 106, using Fourier inversion, by the frequency wavenumber domain postponing outward seismic wavefield data Transform to Frequency-Space Domain, the Frequency-Space Domain seismic wavefield data after being converted.Using substep Fu In leaf time-displacement operator and using described mean-square-root velocity field to conversion after Frequency-Space Domain seismic wave number of fields According to carrying out continuation process, obtain the Frequency-Space Domain seismic wavefield data of secondary continuation.

Calculated for step 105 wave field is transformed into Frequency-Space Domain through Fourier inversion, in this base On plinth, the when transposition for Perturbation, application are calculated by the step Fourier time-displacement operator of time domain Time-displacement operator, realizes the continuation to Perturbation, its expression formula is:

$p{*}_{-u}(w,x,y,\mathrm{\τ})=p{*}_u(w,x,y,\mathrm{\τ})\·e^{{\mathrm{iw\δs}}_{rms}(\mathrm{\τ},x,y)}$

Wherein, δ s_rms(τ, x, y) is the slowness of Perturbation.

So far, complete the wave field extrapolation to geophone station side earthquake record τ moment at imaging point position. Flow process enters into step 107.

In step 107, according to the ray propagation time of described focal point to imaging point, using firing time Image-forming condition, makees phase shift to Frequency-Space Domain seismic wave field and carries out the integration of effective frequency range, obtain Seismic imaging result to big gun record；Record-shifted for big gun imaging is converted into common imaging gather, merges phase Same geophone offset, this image gather can be used for later stage avo analysis and lithological inversion；All single-shots are become As result is superimposed according to locus, or the direct superposition to common imaging gather, obtain the folded of target area Front time migration imaging results.

In one embodiment, Frequency-Space Domain seismic wave field continuation value step 106 being obtained, according to sharp Send out time image condition implementing phase to move and effective frequency range is integrated, obtain final when m- sky Between domain seismic wave field value, its image-forming condition expression formula is:

$i(x,y,t_s)={\left(\frac{1}{2\mathrm{\π}}\right)}^2{\&integral;}_{w1}^{w2}i(x,y,\mathrm{\τ},w)e^{iw(\mathrm{\τ}-t_s)}dw$

Wherein, i is the temporal-spatial field seismic wave field after phase shift, w1 to w2 having for seismic wave Effect frequency band range.

Picture value is become according to described final temporal-spatial field seismic wave field, by its all single-shot imaging results According to locus superposition, or record-shifted for big gun imaging is converted into common imaging gather, to common imaging Point road collection is directly superimposed, just can obtain step Fourier pre-stack time migration imaging knot as shown in Figure 5 Really, compared with the marmousi migration result being obtained using ray method pre-stack time migration shown in Fig. 4, adopt Wave field abundant information in the migration result being obtained with the inventive method, the internal weak reflection in stratum is clear, embodies Guarantor's width of wave field method migration before stack, simultaneously at position shown in square frame, is obtained using the inventive method Fault imaging result improve a lot compared with ray method skew, breakpoint is clear-cut, and resolution is also higher.

Claims (9)

1. the prestack time migration method based on split-step fast fourier transformation is it is characterised in that this is based on The prestack time migration method of split-step fast fourier transformation includes:

Step 1, inputs pretreated geological data p_u(t,x,y)；

Step 2, using pretreated geological data p_u(t, x, y) is calculated root mean sequare velocity spectrum, Root mean sequare velocity is picked up by interactive mode, and obtains mean-square-root velocity field in the range of work area v_rms(t,x,y)；

Step 3, based on mean-square-root velocity field v_rms(t, x, y), the ray calculating imaging point to focal point passes τ between sowing time；

Step 4, using Fourier transformation, by the geological data p of temporal-spatial field_u(t, x, y) transforms to Frequency wavenumber domain p^* _u(w,k_x,k_y), wherein, p^* _u(w,k_x,k_y)=fft (p_u(t,x,y))；

Step 5, using step Fourier phase-shift operator by p^* _u(w,k_x,k_y) directly continuation arrive underground one-tenth On the time τ of picture point, obtain the continuation value of background wave field；

Step 6, the wave field after continuation is fourier transformed Frequency-Space Domain, by time domain Step Fourier time-displacement operator carries out time shift computing, realizes the continuation to disturbance wave field；And

Step 7, according to the ray propagation time τ of imaging point to focal point, using firing time imaging Condition, makees phase shift to Frequency-Space Domain seismic wave field and carries out the integration of effective frequency range, obtain The seismic imaging result of big gun record.

2. the prestack time migration method based on split-step fast fourier transformation according to claim 1, It is characterized in that, in step 1, interval velocity model in depth domain is just being drilled with the common big gun collection p obtaining_u(t,x,y) Carry out denoising, these conventional pretreatment of static correction.

3. the prestack time migration method based on split-step fast fourier transformation according to claim 1, It is characterized in that, the root mean sequare velocity of seed point location in step 2, is picked up by interactive mode, Smooth the mean-square-root velocity field v obtaining target area through three-dimensional interpolation_rms(t, x, y), described root mean sequare velocity Field is for the step Fourier pre-stack time migration to geological data.

4. the prestack time migration method based on split-step fast fourier transformation according to claim 3, It is characterized in that, in step 2, using pretreated geological data p_u(t, x, y) calculates root-mean-square Normal-moveout spectrum, by interactive mode, picks up the root mean sequare velocity of seed point location at equal intervals according to 100 meters, Then the time domain mean-square-root velocity field of the model being spaced apart 10 meters is obtained by interpolation smoothing v_rms(t, x, y), i.e. velocity field needed for pre-stack time migration.

5. the prestack time migration method based on split-step fast fourier transformation according to claim 1, It is characterized in that, in step 3, based on mean-square-root velocity field v_rms(t, x, y), is calculated using ray method Go out imaging point to the ray propagation time of focal pointWherein, τ is imaging The time of point, x is the position of imaging point, x_sFor the position of focal point, v_rmsFor root mean sequare velocity.

6. the prestack time migration method based on split-step fast fourier transformation according to claim 1, It is characterized in that, in steps of 5, by the mean-square-root velocity field in application time domain, prolonged by single step Open up and obtain, the mutually transposition of background velocity is directed on continuation time τ, described phase-shift operator expression formula is such as Under:

$p{*}_u(w,k_x,k_y,\mathrm{\τ})=p{*}_u(w,k_x,k_y,0)\·e^{i\mathrm{\τ}\sqrt{w^2{s^2}_{rms0}\left(\mathrm{\τ}\right)-k_x^2-k_y^2}}$

Wherein, v_rms0(τ) for the background root-mean-square field speed angle value in τ moment, s_rms0(τ) it is the slow of ambient field Degree, and s_rms0(τ)=1/v_rms0(τ), w is frequency, k_xFor the wave number in x direction, k_yFor y direction Wave number.

7. the prestack time migration method based on split-step fast fourier transformation according to claim 1, It is characterized in that, in step 6, calculated for step 5 wave field is changed through Fourier inversion To Frequency-Space Domain, it is calculated by the step Fourier time-displacement operator of time domain on this basis For the when transposition of Perturbation, apply time-displacement operator, realize the continuation to Perturbation, its expression formula is:

$p_{-u}^{*}(w,x,y,\mathrm{\τ})={p^{*}}_u(w,x,y,\mathrm{\τ})\·e^{{\mathrm{iw\δs}}_{rms}(\mathrm{\τ},x,y)}$

Wherein, δ s_rms(τ, x, y) is the slowness of Perturbation, so far, completes to the earthquake of geophone station side The wave field extrapolation in record τ moment at imaging point position.

8. the prestack time migration method based on split-step fast fourier transformation according to claim 1, It is characterized in that, in step 7, Frequency-Space Domain seismic wave field continuation value that step 6 is obtained, Move according to firing time image-forming condition implementing phase and effective frequency range is integrated, obtain final Temporal-spatial field seismic wave field value, its image-forming condition expression formula is:

$i(x,y,t_s)={\left(\frac{1}{2\mathrm{\π}}\right)}^2{\&integral;}_{w1}^{w2}i(x,y,\mathrm{\τ},w)e^{iw(\mathrm{\τ}-t_s)}dw$

Wherein, i is the temporal-spatial field seismic wave field after phase shift, and w1 to w2 is seismic wave Effective band scope.

9. the prestack time migration method based on split-step fast fourier transformation according to claim 1, It is characterized in that, step 7 also includes: record-shifted for big gun imaging is converted into common imaging gather, closes And identical geophone offset；All single-shot imaging results are superimposed according to locus, or to common imaging point Road collection is directly superimposed, and obtains the pre-stack time migration imaging results of target area.