Elastic reverse-time migration system and method using absolute value function for improving the quality of subsurface structure imaging
Provided is elastic reverse-time migration system and method using an absolute value function for improving the quality of subsurface structure images, and more particularly, elastic reverse-time migration system and method using an absolute value function for improving the quality of subsurface structure images capable of minimizing waveform changing by separating wavefields using stress-displacement relationships and improving accuracy of the subsurface structure images by applying the absolute value function to migration images.
1. An elastic reverse-time migration system, comprising:
a virtual source calculation unit being input seismic data and a subsurface structure model to calculate a virtual source;
a virtual source wavefield calculation unit calculating a virtual source wavefield from the calculated virtual source;
a back-propagated wavefield calculation unit loading the seismic data to perform back propagation processing and calculate a back-propagated wavefield;
a virtual source wavefield waveform separation unit using stress-displacement relationships to decompose P-wavefield from the virtual source wavefield;
a back-propagated wavefield waveform separation unit using the stress-displacement relationships to decompose P-wavefield from the back-propagated wavefield; and
a convolution unit convoluting the two wavefields decomposed by the virtual source wavefield waveform separation unit and the back-propagated wavefield waveform separation unit, respectively,
wherein the stress-displacement relationships satisfy the following Equation
τ
xx
=
(
λ
+
2
μ
)
∂
u
x
∂
x
+
λ
∂
u
z
∂
z
τ
zz
=
(
λ
+
2
μ
)
∂
u
z
∂
z
+
λ
∂
u
x
∂
x
(in the above Equation, λ and μ represent the Lame's parameters, τ xx and τ zz represent stress tensors, u x and u z represent displacements, respectively, for the x- and z-axes).
2. The elastic reverse-time migration system of claim 1 , further comprising:
an image quality improvement unit applying an absolute value function to migration images obtained by the convolution of the convolution unit.
3. An elastic reverse-time migration method, comprising:
a) loading seismic data and subsurface structure model data;
b) calculating a virtual source on the basis of the input data and calculating a virtual source wavefield;
c) performing back propagation processing on the seismic data to calculate a back-propagated P-wavefield;
d) decomposing a P-wavefield from the virtual source wavefield using stress-displacement relationships;
e) decomposing a wavefield form the back-propagated wavefield using the stress-displacement relationships; and
f) convoluting the two wavefields decomposed in the step c) and the step e), respectively,
wherein the stress-displacement relationships satisfy the following Equation
τ
xx
=
(
λ
+
2
μ
)
∂
u
x
∂
x
+
λ
∂
u
z
∂
z
τ
zz
=
(
λ
+
2
μ
)
∂
u
z
∂
z
+
λ
∂
u
x
∂
x
(in the above Equation, λ and μ represent the Lame's parameters, τ xx and τ zz represent stress tensors, u x and u z represent displacements respectively, for the x- and z-axes).
4. The elastic reverse-time migration method of claim 3 , further comprising:
g) applying an absolute value function to migration images obtained by the convolution in the step f).