Transcript ppt - Georgia Institute of Technology

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
(Left) Seismicity in Taiwan.
(Right) The sketch showing the geologic
cross section of Chelungpu fault (Teng
1990).
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.
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).
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.
Result
Autocorrelation
functions of
CC>=0.90 at the
E-W (a) and N-S
(b) components
Result
Time delays measured from E-W and N-S components
versus occurrence times of 707 events with waveform
correlation coefficient ≥ 0.85.
Result
The time delays in
Z components of
CC>=0.85
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
Kevin Chao