阅读说明：本技术 一种瑞雷面波频散曲线快速反演方法 (Rayleigh surface wave frequency dispersion curve rapid inversion method ) 是由 王姣 闫月锋 周大永 薛亨泰 王泽� 于 2020-12-25 设计创作，主要内容包括：本发明公开了一种瑞雷面波频散曲线快速反演方法,涉及面波勘探领域。瑞雷面波频散曲线快速反演方法,对于层状介质,将其瑞雷面波的频散方程简写为隐函数形式,瑞雷波频散曲线对介质密度与纵波速度并不敏感,为了提高反演效率,只反演介质厚度与横波速度,在面波反演过程中,首先需要获取反演所需的面波频散值E-(观测),获取频散值之后,若所有需反演模型参数组合P共有m组,由于频散方程的非线性,进行目标函数定义,将已知频散值与模型参数代入频散方程,计算频散方程的值作为目标函数的值。该方法即可以避免对不同模式频散数值的区分,又免去了计算频散速度值的过程,因而可以极大地提高运算效率,提高反演速度。(The invention discloses a Rayleigh surface wave frequency dispersion curve rapid inversion method, and relates to the field of surface wave exploration. A method for quickly inverting Rayleigh surface wave frequency dispersion curve includes that for a layered medium, a frequency dispersion equation of Rayleigh surface waves of the layered medium is abbreviated to be in an implicit function form, the Rayleigh surface wave frequency dispersion curve is insensitive to medium density and longitudinal wave speed, only medium thickness and transverse wave speed are inverted in order to improve inversion efficiency, and in the surface wave inversion process, a surface wave frequency dispersion value E needed by inversion needs to be obtained firstly Observation of After obtaining the dispersion values, if all model parameter combinations P to be inverted have m groups, defining the target function due to nonlinearity of the dispersion equation, substituting the known dispersion values and the model parameters into the dispersion equation, and calculating the values of the dispersion equation as the values of the target function. The method can avoid distinguishing the frequency dispersion values of different modes, and also avoids the process of calculating the frequency dispersion speed value, thereby greatly improving the operation efficiency and the inversion speed.)

1. A fast inversion method of Rayleigh surface wave dispersion curve is characterized in that,

for a layered medium, the dispersion equation of the Rayleigh surface wave is abbreviated as an implicit function form shown in formula (1):

F(V_p,V_s,ρ,h,f_i,V_ri)＝0 (1)

wherein f is_iIs the frequency, V_riIs the phase velocity of Rayleigh surface waves, V_p＝(V_p(1),V_p(2),…,V_p(n)) Vector formed by longitudinal wave velocity of medium of each layer of the geological model, V_s＝(V_s(1),V_s(2),…,V_s(n)) A vector formed by the transverse wave velocity of each medium layer of the geological model, wherein rho is (rho)₍₁₎,ρ₍₂₎,…,ρ_(n)) A vector formed by the density of each layer of medium of the geological model, h ═ h₍₁₎,h₍₂₎,…,h_(n-1)Infinity) is a vector formed by the thickness of each layer of medium (including half space) of the geological model, and the total number is 4n-1 parameters;

the Rayleigh wave dispersion curve is insensitive to medium density and longitudinal wave velocity, only medium thickness and transverse wave velocity are inverted in order to improve inversion efficiency, and a surface wave dispersion value E required by inversion needs to be obtained in a surface wave inversion process_{Observation of}As shown in formula (2):

in the formula, V_{Observation of}And f_{Observation of}After obtaining the dispersion values for the dispersion curve observed values extracted from the actual data, if all model parameter combinations P to be inverted have m groups, as shown in formula (3):

P_j＝(V_sj,h_j),(j＝1,2,…,m) (3)

in the formula V_sjAnd h_jThe method comprises selecting formula (4) as objective function OBV according to artificially set transverse wave velocity and thickness of each layer of geological model and nonlinearity of frequency dispersion equation_jDefining:

OBV_j＝F(V_p,V_sj,ρ,h_j,f_{observation of},V_{Observation of}),(j＝1,2,…,m) (4)

And substituting the known dispersion value and the model parameter into the dispersion equation, and calculating the value of the dispersion equation as the value of the target function.

Technical Field

The invention relates to the field of surface wave exploration, in particular to a Rayleigh surface wave frequency dispersion curve rapid inversion method.

Background

Rayleigh surface wave exploration is widely applied to geological exploration and engineering detection at present as a novel shallow seismic exploration method. Because the prior surface wave inversion method needs to calculate the velocity value when the dispersion equation is zero, the calculated amount in the forward process is increased, and the inversion speed is reduced.

Disclosure of Invention

The invention aims to provide a fast inversion method of a Rayleigh surface wave frequency dispersion curve, which utilizes a Monte Carlo algorithm to invert the frequency dispersion curve extracted from a surface wave field.

The invention specifically adopts the following technical scheme:

a Rayleigh surface wave frequency dispersion curve rapid inversion method is characterized in that for a layered medium, a frequency dispersion equation of a Rayleigh surface wave is abbreviated as an implicit function form shown in formula (1):

F(V_p,V_s,ρ,h,f_i,V_ri)＝0 (1)

wherein f is_iIs the frequency, V_riIs the phase velocity of Rayleigh surface waves, V_p＝(V_p(1),V_p(2),…,V_p(n)) Vector formed by longitudinal wave velocity of medium of each layer of the geological model, V_s＝(V_s(1),V_s(2),…,V_s(n)) A vector formed by the transverse wave velocity of each medium layer of the geological model, wherein rho is (rho)₍₁₎,ρ₍₂₎,…,ρ_(n)) A vector formed by the density of each layer of medium of the geological model, h ═ h₍₁₎,h₍₂₎,…,h_(n-1)Infinity) is a vector formed by the thickness of each layer of medium (including half space) of the geological model, and the total number is 4n-1 parameters;

the Rayleigh wave dispersion curve is insensitive to medium density and longitudinal wave velocity, only medium thickness and transverse wave velocity are inverted in order to improve inversion efficiency, and a surface wave dispersion value E required by inversion needs to be obtained in a surface wave inversion process_{Observation of}As shown in formula (2):

in the formula, V_{Observation of}And f_{Observation of}After obtaining the dispersion values for the dispersion curve observed values extracted from the actual data, if all model parameter combinations P to be inverted have m groups, as shown in formula (3):

P_j＝(V_sj,h_j),(j＝1,2,…,m) (3)

in the formula V_sjAnd h_jThe method comprises selecting formula (4) as objective function OBV according to artificially set transverse wave velocity and thickness of each layer of geological model and nonlinearity of frequency dispersion equation_jDefining:

OBV_j＝F(V_p,V_sj,ρ,h_j,f_{observation of},V_{Observation of}),(j＝1,2,…,m) (4)

And substituting the known dispersion value and the model parameter into the dispersion equation, and calculating the value of the dispersion equation as the value of the target function.