Earthquake Triggering and Fault Interaction in a Thrust
Fault System: the 1999 Chi-Chi, Taiwan, Earthquake
Kuo-Fong Ma, Chung-Han Chan
Institute of Geophysics, National Central University, Jung-Li 320-54, Taiwan, ROC.
Ross S. Stein
U.S. Geological Survey, Menlo Park, CA 94025
To understand the earthquake triggering and possible fault interaction in a thrust fault
system, we calculate the Coulomb stress change associated with the 1999 Chi-Chi, Taiwan,
earthquake. The Coulomb stress change for the ruptured Chelungpu fault with thrust
faulting mechanism, associated with the earthquake shows broad positive distribution of
Coulomb stress change both in space and depth. The correlation of the Coulomb stress
change to the aftershocks is significant. The triggering of the aftershocks has the Coulomb
stress change of less than 1 bar in off-source region, especially to the northeastern of the
fault. The thrust faulting mechanism of the Chi-Chi earthquake triggers the aftershocks
distributed in southeastern direction with strike-slip focal mechanisms in the southern tip
of the thrust fault. Even though the Coulomb stress change of the earthquake is up to about
500 bars, the calculated Coulomb stress change for the optimal fault planes of the M>6
aftershocks are mostly about 2-5 bars. It suggests that the occurrences of the large
aftershocks are not necessary in the region with large Coulomb stress change. The
Coulomb stress change for the fault system associated with the Chi-Chi earthquake shows
significant stress relaxation for the thrust faults to the east of the ruptured Chelungpu fault.
The imparted positive stress on the faults, the Changhua and Chiko faults, to the west and
south of the Chelungpu fault are prominent. Comparison with historical events since 1600,
the calculated Coulomb stress change shows strong correlation of the occurrences of the
historical earthquake on the Chelungpu fault to the events on Changhua and Chiko faults.
It suggests the possible predictive power of the static stress calculation in estimating
occurrences of future large earthquakes.