Finite Source Imaging of Seismogenic Structures of Central Taiwan: Results from six Mw > 5.8 Chi-Chi, Taiwan Aftershocks
Abstract
Central Taiwan is located in the collision zone between the Luzon arc of Philippine Sea plate and the Chinese passive margin of the Eurasia plate. Here the Chinese passive margin, with normal and strike-slip fault structures, enters into the convergent boundary where contractional processes dominate. Recently, the 1999, Chi-Chi sequence provides a great opportunity using earthquake sources to map the deep crustal structures of Central Taiwan. Several seismicity and moment tensor studies have already illuminated the geometry of important seismogenic faults at depth. We want to connect these data points using the planar slip models derived from finite fault inversions using strong motion data of 6 large aftershocks of the Chi-Chi, Taiwan earthquake. For each event, we derived a preferred model by testing different focal mechanisms, hypocenters, rupture velocities, and dislocation rise times, as well as different combinations of stations in more than 1000 inversions. We have assigned high levels of confidence for 3 of the preferred slip models. Two of them ruptured on the southern extension of the mainshock fault plane along the Puli-Chusan lineation. In cross section these two aftershocks form a flat-ramp geometry. One strike-slip aftershock nucleated within the basement but ruptured mainly within the overlying sedimentary strata, suggesting that seismogenic deformation in the basement can influence shallow structures. We assigned lower levels of confidence for the remaining slip models because other geophysical data were needed for interpretation, even though their waveform fits are also good. One aftershock occurred on a west-dipping backthrust at shallow depth near the town Puli. Another aftershock ruptured on a west-dipping fault in the basement. One aftershock near the town Chaiyi shows slightly better waveform fits for a west-dipping fault plane in the basement. The steep dip angles of these basement-involved slip models suggest that these events ruptured on pre-existing weak zones, presumably normal faults along the passive margin. In sum, this study imaged fault structures in the vicinity of proposed decollement. But at the same time, there were also strong evidence for basement-involved co-seismic deformation in the basement and above the decollement.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.T11F..02C
- Keywords:
-
- 7230 Seismicity and seismotectonics;
- 8102 Continental contractional orogenic belts;
- 8107 Continental neotectonics;
- 8123 Dynamics;
- seismotectonics;
- 9320 Asia