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Kevin Chao, Zhigang Peng

Temporal Changes of Shear Wave Velocity and Anisotropy in the Shallow Crust Induced by the 10/22/1999 M6.4 and M6.0, Chia-Yi, Taiwan Earthquake. Kevin Chao, Zhigang Peng. School of Earth and Atmospheric Sciences, Georgia Institute of Technology. EAS Symposium, 11/02/2007. Motivation.

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Kevin Chao, Zhigang Peng

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  1. Temporal Changes of Shear Wave Velocity and Anisotropy in the Shallow Crust Induced by the 10/22/1999 M6.4 and M6.0, Chia-Yi, Taiwan Earthquake Kevin Chao, Zhigang Peng School of Earth and Atmospheric Sciences, Georgia Institute of Technology EAS Symposium, 11/02/2007

  2. Motivation (Left) Seismicity in Taiwan. (Right) The sketch showing the geologic cross section of Chelungpu fault (Teng 1990).

  3. Study Area Schematic diagram showing the location of 200m-deep borehole station CHY and direct (upgoing) and surface-reflected (downgoing) waves. The topographical map showing the study area in central Taiwan, and the Cross-section view of seismicity around station CHY.

  4. Anisotropy Schematic diagram of shear wave splitting in the case of two anisotropic layers. The incoming shear wave is split twice, leading to four idvividual waves at the receiver (Tardley & Crampin 1991).

  5. Auto-Correlation Function (a) Example seismograms in E-W (fast), N-S (slow), and Z (vertical) components. (b) Results of autocorrelation function for two horizontal components.

  6. Result Autocorrelation functions of CC>=0.90 at the E-W (a) and N-S (b) components

  7. Time delays measured from E-W and N-S components versus occurrence times of 707 events with waveform correlation coefficient ≥ 0.85. Result

  8. Result The time delays in Z components of CC>=0.85

  9. Conclusions The time delays in both E-W (fast) and N-S (slow) components increased by ~3 percent, but no clear time delay change in Z component at the time of the Chia-Yi mainshock.The time difference did not change between N-S and E-W. The shear-wave anisotropy in the top 200 m of the crust no clear change. Fluid-Filled microcrack models

  10. Thank you! Kevin Chao

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