Energy Budget of the 1999 Chichi, Taiwan Earthquake
Abstract
We examined the energy balance of the 1999 Chichi, Taiwan earthquake (Mw 7.6) using several estimates of radiated and thermal energy. Estimates of radiated energy from regional seismograms give a value of about 1.0x10^{16} joules. The static stress drop from the total moment and the fault area is about 3 MPa. Temperature measurements from 2 shallow boreholes in the northern and southern sections of the fault show temperature profiles that increase across the narrow fault zone. If we assume this temperature increase was caused by frictional heating during faulting of the earthquake, thermal modeling gives the results that the fault generated 2.5 x10^{6} joules per square meter in the north and 4.5 x 10^{6} joules per square meter in the south. If these frictional values are extrapolated to depth, using higher normal pressure, we estimate that the earthquake produced a total of about 2 x 10^{17} joules of frictional heat. Adding the radiated and thermal energy gives a total energy of the earthquake (neglecting the fracture energy) of about 2.1 x 10^{17} joules. This implies an average seismic efficiency is about 5%. The average energy values for the earthquake can be quite different from the energy balance on smaller portions of the fault. For example, most of the radiated energy is generated by a large asperity on the northern part of the fault, which has an area that is about 20% of the whole fault surface. For this region of large slip, it has been suggested that the dynamic friction may be very low. If we use a value of 0.2 for the coefficient of friction, which is consistent with the borehole temperature data, the thermal energy for region of the asperity will be about 3x10^{16} joules and the seismic efficiency for the asperity is about 30%, which is much higher than the average value for the whole earthquake.
 Publication:

AGU Fall Meeting Abstracts
 Pub Date:
 December 2002
 Bibcode:
 2002AGUFM.S71E..09M
 Keywords:

 7209 Earthquake dynamics and mechanics;
 7215 Earthquake parameters