CN106154325A - Relief surface based on ray theory combination source wavefield orientation method - Google Patents

Abstract

The invention provides a kind of relief surface based on ray theory combination source wavefield orientation method.This method is the combination source wavefield orientation method expansion under the conditions of non uniform land surface under the conditions of relief surface.The method exciting time delay relative to conventional geometric path computing, this method ray theory based on high-frequency approximation, the computational problem exciting time delay by combination focus to virtual wavefront surface, regard the computational problem of seimic travel time in non-uniform dielectric as, the seimic travel time field function of epicenter excitation is obtained by solving eikonal equation, and obtain list when walking of wavefront surface with the wavefront surface equations simultaneousness orienting wave field, obtain according to Fermat's principle and excite time delay accurately.Through numerical experimentation, the inventive method can obtain the seismic wave field of the direction propagation under the conditions of relief surface, and can eliminate the heterogeneity impact on seismic wave field on earth's surface.

Description

Relief surface based on ray theory combination source wavefield orientation method

Technical field

The present invention relates to a kind of method of seismic prospecting, the relief surface combination source wavefield being based especially on ray theory is fixed To method, it is the popularization under the conditions of non-homogeneous relief surface of the wave field orientation method.

Background technology:

Combination focus is to be arranged according to certain rule by multiple single sources, sets each epicenter excitation time delay or phase place respectively Difference, interferes superposition by multiple single sources so that the propagation of seismic wave has directive exciting method.On the one hand, Combination focus method improves the excitation energy of seismic prospecting by superposition, thus improves the noise of target zone echo Ratio；On the other hand, directivity and the focusing of wave field have more preferable Effect on Detecting for some structure with plastid obliquely, permissible Improve the seismic prospecting detectivity to underground specific objective body.

Generally simple linear combination focus is to be disposed with limit focus on horizontal earth's surface, and adjacent sources spacing is fixed, design Fix and excite time delay, and obtain the seismic wave field of direction initialization according to the direction factor formula of shooting on group.If earth's surface is uniform Declined ground, base area inclination layer derivation can tilt shooting on group direction factor formula；If earth's surface is uniform pitch complicated earth surface, Available huygens-fresnel principle, rotates horizontal earth's surface coordinate to the tilt coordinates orienting wave field normal direction, can be according to geometry Path and uniform top layer speed, obtain combination focus excites " Chinese Journal of Geophysics " 2014 such as delay parameter, Gong Xiangbo, rises and falls Ground table pack focus seismic wave field orientation method.The technology of forefathers is under the supposed premise of Land Surface Parameters approaches uniformity, and real Border ground observation geological conditions often complexity, the most heterogeneous.

Summary of the invention:

The purpose of the present invention is aiming at above-mentioned the deficiencies in the prior art, it is provided that a kind of rough ground based on ray theory Table pack source wavefield orientation method, it is expanded combination focus method application in the case of non-homogeneous relief surface, is allowed to more There is general applicability.

Main idea is that based on ray theory calculate combination focus excite delay parameter, by epicenter excitation The Solve problems of time delay regards seimic wave propagation as to the computational problem of the most virtual wavefront surface hourage, can effectively be applicable to earth's surface The heterogeneity condition of medium.

It is an object of the invention to be achieved through the following technical solutions:

Relief surface based on ray theory combination source wavefield orientation method, comprises the following steps:

A, on relief surface model N number of single source of the horizontal interval such as layout, S₁,S₂,…,S_n；

B, define any one focus as zero S_t

Any one integer of 1 n (t be), sets up cartesian coordinate system x-z on horizontal earth's surface；

C, the virtual wavefront surface of definition orientation wave field, the seismic wave field direction of propagation is θ with vertically apparent bearing angle, is referred to as The deflection that orientation wave field is propagated, under the coordinate system of horizontal earth's surface, virtual wavefront surface is z=tan (θ) x；

D, by focus S at zero_tThe time delay that excites be set to zero τ_St=0；

E, using remaining focus in assembled arrangement to virtual wavefront surface excite time delay as seismic wave in non-uniform dielectric When walking of propagation, is calculated by ray theory formula；

Except focus S in f, general's combination focus_tRemaining focus, calculate successively according to step e and excite time delay τ_S2,…,τ_Sn；

G, respectively according to calculate after delay parameter excite each focus, oriented by the interference principle of stacking of wave field Seismic wave field.

Ray theory formula described in step e:

1) according to ray theory, wave equation, in the case of high-frequency approximation, is reduced to seismic travel time field function Eikonal equation, solves eikonal equation and obtains S under two-dimensional case₁Epicenter excitation time field function is t_S1(x,z)；

2) simultaneous S₁Source time field function t_S1(x, z) with virtual wavefront surface coordinate z=tan (θ) x, tries to achieve S₁Focus Whilst on tour list t at virtual wavefront surface_S1(x,tan(θ)·x)；

3) according to Fermat's principle, the list hourage minimizing upper step calculated, as S₁Focus excite time delay, I.e. τ_S1=min (t_S1(x, tan (θ) x)), min is for taking minimum value function；

Beneficial effect: through test, method disclosed by the invention calculated combination epicenter excitation time delay is accurate, can obtain To the stable orientation seismic wave field propagated.The present invention is applicable to complicated relief surface situation, and not horizontal the most anisotropically by earth's surface Ball physical parameter factor affects, and can improve the seismic method ability to specifically descending objective body to detect.From figure 3, it can be seen that The inventive method eliminates the impact that orientation wave field is propagated by relief surface heterogeneity.

Accompanying drawing explanation

Fig. 1 non-homogeneous relief surface illustraton of model

Fig. 2 is field isogram when walking that focus is positioned at model diverse location

Fig. 2 a is focus when being positioned at model left end,

Fig. 2 b is focus when being positioned in the middle of model,

Fig. 2 c is focus when being positioned at model right-hand member,

It is the seimic travel time field isogram calculated according to ray theory, is to be asked by numerical value in a g step of the present invention Solution eikonal equation is tried to achieve.

Fig. 3 is the orientation wave field snapshot plotting using the present invention to obtain

Fig. 3 a be guided wave field direction angle be-30 wave field snapshot plottings when spending

Fig. 3 b be guided wave field direction angle be wave field snapshot plotting when 0 degree

Fig. 3 c be guided wave field direction angle be wave field snapshot plotting when 30 degree,

Detailed description of the invention

The present invention is described in further detail with embodiment below in conjunction with the accompanying drawings.

A kind of relief surface based on ray theory combination source wavefield orientation method, in the non-homogeneous fluctuating shown in Fig. 1 Under terrain model, comprise the steps:

A, on relief surface model N number of single source of the horizontal interval such as layout, S₁,S₂,…,S_n；

B, define any one focus as zero S_t(t is 1 any one integer arriving n), sets up horizontal earth's surface Cartesian coordinate system x-z；

C, the virtual wavefront surface of definition orientation wave field, if the seismic wave field direction of propagation is θ with vertically apparent bearing angle, claim The deflection propagated for orientation wave field, under the coordinate system of the most horizontal earth's surface, virtual wavefront surface is z=tan (θ) x, and wherein tan is just Cut function；

D, by focus S at zero_tThe time delay that excites be set to zero τ_St=0；

E, using remaining focus in assembled arrangement to virtual wavefront surface excite time delay as seismic wave in non-uniform dielectric When walking of propagation, is calculated by ray theory formula；

1) first, according to ray theory, wave equation is in the case of high-frequency approximation, when can be reduced to about seimic wave propagation Between the eikonal equation of field function, i.e. obtain the seimic travel time distribution situation of certain epicenter excitation by solving eikonal equation.With S₁Illustrating as a example by focus, numerical solution eikonal equation obtains S under two-dimensional case₁The time field function of epicenter excitation is t_S1(x, z), Eikonal equation is defined as following formula；

${\left(\frac{\∂t(x,z)}{\∂x}\right)}^2+{\left(\frac{\∂t(x,z)}{\∂z}\right)}^2=\frac{1}{v{(x,z)}^2}$

Wherein (x z) is two dimension non-uniform velocities field, hypocentral location coordinate and the zero moment initial strip as equation solution to v Part, can use in the case of relief surface that the up-wind finite-difference under body fitted grids coordinate is discrete solves this equation；

2) secondly, simultaneous S₁Source time field function t_S1(x, z) with virtual wavefront surface coordinate z=tan (θ) x, tries to achieve S₁ Focus is whilst on tour list t at virtual wavefront surface_S1(x,tan(θ)·x)；

3) again, according to Fermat's principle, the list hourage minimizing upper step calculated, as S₁Exciting of focus Time delay, i.e. τ_S1=min (t_S1(x, tan (θ) x)), min is for taking minimum value function；

Except focus S in f, general's combination focus_tRemaining focus, calculate e.1, e.2, the most successively according to step excites Time delay τ_S2,…,τ_Sn；

G, respectively according to calculate after delay parameter excite each focus, oriented by the interference principle of stacking of wave field Seismic wave field.

Claims (2)

1. relief surface based on a ray theory combination source wavefield orientation method, it is characterised in that comprise the following steps:

A, on relief surface model N number of single source of the horizontal interval such as layout, S₁,S₂,…,S_n；

B, define any one focus as zero S_t

Any one integer of 1 n (t be), sets up cartesian coordinate system x-z on horizontal earth's surface；

C, the virtual wavefront surface of definition orientation wave field, the seismic wave field direction of propagation is θ with vertically apparent bearing angle, is referred to as orientation The deflection that wave field is propagated, under the coordinate system of horizontal earth's surface, virtual wavefront surface is z=tan (θ) x；

D, by focus S at zero_tThe time delay that excites be set to zero τ_St=0；

E, using remaining focus in assembled arrangement to virtual wavefront surface excite time delay as seimic wave propagation in non-uniform dielectric When walking, calculated by ray theory formula；

Except focus S in f, general's combination focus_tRemaining focus, calculate successively according to step e and excite time delay τ_S2,…,τ_Sn；

G, respectively according to calculate after delay parameter excite each focus, by the interference principle of stacking of wave field obtain orient earthquake Wave field.

2. combining source wavefield orientation method according to the relief surface based on ray theory described in claim 1, its feature exists In, the ray theory formula described in step e:

1) according to ray theory, wave equation, in the case of high-frequency approximation, is reduced to the eikonal of seismic travel time field function Equation, solves eikonal equation and obtains S under two-dimensional case₁Epicenter excitation time field function is t_S1(x,z)；

2) simultaneous S₁Source time field function t_S1(x, z) with virtual wavefront surface coordinate z=tan (θ) x, tries to achieve S₁Focus is virtual Whilst on tour list t at wavefront surface_S1(x,tan(θ)·x)；

3) according to Fermat's principle, the list hourage minimizing upper step calculated, as S₁Focus excite time delay, i.e. τ_S1 =min (t_S1(x, tan (θ) x)), min is for taking minimum value function.