HR: 11:40h
AN: T11F-06    [PDF]
TI: Fault Slip Rates From Repeating Microearthquakes on the Chihshang Fault, Eastern Taiwan
AU: * Chen, H
EM: l4890102@ccmail.ncku.edu.tw
AF: Department of Earth Sciences, National Cheng Kung University, Tainan, 701 Taiwan
AU: Rau, R
EM: raurj@mail.ncku.edu.tw
AF: Department of Earth Sciences, National Cheng Kung University, Tainan, 701 Taiwan
AB: The Chihshang fault is the most active segment of the collision boundary between Eurasia and the Luzon arc of the Philippine Sea plate in eastern Taiwan. Seismicity study shows that the Chihshang fault is a narrow SE-dipping listric thrust extending from near surface to a depth of 25 km. Geodetic measurements indicate a 2 cm/yr surface slip rate on the Chihshang fault, however, the fault slip behavior at depth is virtually unknown. In this study we determine fault slip rates at depth by using identified clusters of repeating earthquakes with highly similar waveforms. 1487 earthquakes occurred in Chihshang area with magnitude of 1 - 6 recorded by Taiwan Seismic Network from 1991 to 2002 are used. Recurrence intervals and moment release rates from repeating earthquake sequences are analyzed to estimate fault slip rates for different sequences. Event pairs with waveform cross-correlation coefficient larger than 0.9 at two or more stations are selected as the earthquake repeaters. For the data we have processed so far, 17 repeating earthquake sequences recurred 3 to 9 times are found. Those sequences show both quasi-periodic (recurrence intervals of 0.6 - 4.3 years) and aperiodic types with magnitude range of 2.1 - 3.8 at 12 - 23 km depths. Calculated fault slip rates vary from a constant rate (2.2 cm/yr) at depths of 12 - 15 km to a gradually increase rate (4.2 - 6.5 cm/yr) from depths of 17 to 21 km. Five aperiodic sequences showing irregular recurrence intervals are likely influenced by the occurrences of nearby 1995 M5 earthquakes. The constant 2.2 cm/yr slip rate at 12 - 15 km depth range is consistent with surface creep rate (2 cm/yr) as observed from geodetic measurements. This suggests that the Chihshang fault may have a very shallow locking depth so as to allow the fault creeps freely from surface to a depth of 12 km. Future efforts will focus on completing the search for repeating earthquake sequences and calculating the subsurface slip rates on the Chihshang fault.
DE: 1645 Solid Earth
DE: 1734 Seismology
DE: 1744 Tectonophysics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting