Preseismic Deformation and Coseismic Displacements Associated with
the 1999 Chi-Chi,Taiwan, Earthquake
Yi-Chun Tsai
Abstract
The 1999 Chi-Chi, Taiwan, earthquake (Mw 7.5) produced and
approximately 100-km-long surface rupture, along the north-south
-trending Chelungpu fault. Preseismic deformation in central Taiwan
is realized from annually repeated GPS data acquired during the
1992-1999. The total WNW-ESE shorting rate in the vicinity of the
epicentral region, is up to 25mm/yr. The crustal deformation before
Chi-Chi earthquake was a uniaxial compressional strain of 0.36£gstrain/yr
in the direction of 114¢X.
The GPS measurements taken 0.2-2.7 yr before and within 3 months
after mainshock were utilized to estimate the coseismic displacements.
Horizontal movements of 1.1-1.9 m in the NW-NNW direction are
observed on the hanging wall. Much smaller SE-SEE movements of
0.1-0.5 m are found on the footwall. Vertical offsets of 1.2-4.4 m with
the eastern side up are also observed, and the stations on the footwall
show subsidence of 0.02-0.26 m.
Postseismic displacements as much as 14 cm were recorded by GPS
measurements in the 3 months following the Chi-Chi earthquake.
Assuming the shallow fault dips 24¢XE, the author invert for the deeper
fault geometry. The results show that a deeper horizontal decollement is
in depth range of 8-12 km, and the maximum slip of 25 cm in hypocentral
region at 7-12 km depth.
References
Shui-Beih Yu(2001). Preseismic Deformation and Coseismic Displacements
Associated with the 1999 Chi-Chi, Taiwan , Earthquake,Bulletin of the
Seismological Society of America,Vol.91,No.5
(Abstract)(Full text)
Ya-Ju Hsu(2002). Rapid afterslip following the 1999 Chi-Chi, Taiwan,
Earthquake,Geo. Res. Let.,Vol.29,No.16
(Abstract)(Full text)
Course: Seminar II (for second-year MSc students)