HR: 0830h
AN: S41E-0128    [PDF]
TI: Accuracy Investigation of Seismic Reciprocity Using 3D FDM code
AU: * Poor Moghaddam, P
EM: ppoor@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University Of Tokyo, 1-1-1 Yayoi, Bunkyo-ku,, Tokyo, 113-0032 Japan
AU: Kasahara, J
EM: kasa2@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University Of Tokyo, 1-1-1 Yayoi, Bunkyo-ku,, Tokyo, 113-0032 Japan
AB: Application of Reciprocity theorem for the problem of marine seismology, which there is numerous shots on the surface and few receivers on the bottom of the ocean, is pivotal. The theory of reciprocity states that we can switch the location and direction of the force source and displacement component between source and receiver without changing in the observation waveform. In this work we performed a numerical simulation. In this simulation we solved wave propagation equations using Finite Difference method, which is 4th order in space and 2nd order in time. To investigate whether the discretizing affects the seismic reciprocity we calculate the 2D velocity components (x, z) respected to two orthogonal force components applied in the x and z directions. Finally reciprocal waveforms are compared. The degree of correlation between the reciprocal components is quite high which shows the excellency of the FDM method, which we employed. The structure for this work is obtained from 2D travel-time inversion estimated in the 1996 survey along North-South line at the Sanriku, Japan Trench. The size of this structure is 143km by 30 km (Fig.1), which discretized by 25 meter gird spacing. The structure is completely heterogeneous which any point has its own value of P-velocity, S-velocity and density. In this structure, two points for investigation of reciprocity are considered (Fig.1). A force source was applied in one point and the velocity measured in another point, further the directions and locations of source and receiver were interchanged to measure its reciprocal one. Figures 2 shows z-velocity component and its reciprocal one and the difference between them when a force source applied in the z-direction. Figures 3 shows x-velocity component and its reciprocal one and the difference between them when a force source applied in the x-direction. The source waveform is considered the Ricker wavelet with central frequency of 5 Hz. To gain faster computational time and further improvements, we used Earth Simulator to run our program. The program parallelized using classical method of parallelization on this supercomputer. The computational time is surprisingly faster than Earthquake Research Institute supercomputer; Origin 2000
DE: 3025 Marine seismics (0935)
DE: 3210 Modeling
DE: 3230 Numerical solutions
DE: 4255 Numerical modeling
DE: 4275 Remote sensing and electromagnetic processes (0689)
SC: Seismology [S]
MN: 2003 Fall Meeting