HR: 0800h
AN: T11D-1298    [Abstracts]
TI: Seismogenic Structures Deduced from 3D Spatial Analysis for 1999 M$_{L}$ 6.4 Chaiyi Earthquake Sequences
AU: * Kuo, Y
EM: yutingkuo@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Wu, Y
EM: drymwu@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Chen, H
EM: b88204041@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Chang, C
AF: Seismology Center, Central Weather Bureau, No.64, Gongyuan Rd., Taipei, 100 Taiwan
AU: Chen, R
AF: Seismology Center, Central Weather Bureau, No.64, Gongyuan Rd., Taipei, 100 Taiwan
AU: Lo, P
EM: pwlo@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Ching, K
AF: Department of Earth Sciences, National Cheng Kung University, No.1, Ta-Hsueh Road, Tainan, 701 Taiwan
AU: Lee, J
EM: jclee@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road Sec. 2, Taipei, 115 Taiwan
AB: Due to the convergent tectonics, Taiwan region undergoes frequent earthquakes including felted and feltless ones. The shallow recorded earthquakes ($<$ 20 km) are mainly distributed in western Taiwan. Among them the larger ones usually bring up damages and casualties due to urbanization over there. Since the earthquakes are generated from the activations of active faults, the distribution of the seismicities can be used as a good tool to image the subsurface faults that is essential to realize the framework of active faults. We evaluate an earthquake sequence that happened in Chaiyi area of southwestern Taiwan to clarify the seismogenic faults. The collected earthquake sequence took place at Chiayi in 1999 (namely Chaiyi earthquake; M$_{L}$ 6.4). In total there are 475 earthquakes including the main shock and aftershocks in ten days. We conducted the Double difference (hypoDD) method to relocate all the earthquakes and then used GOCAD (3-D modeling software) to visually image the seismogenic faults. Focal mechanisms are also solved for larger earthquakes (M$_{L}$ $>$ 4) to further check the faulting behavior. On the other hand, we independently reconstructed another structural model based on available subsurface and surface geological data. By comparison of two structural models, we found the seismogenic falults are closely related to the neotectonic system exposed on the ground surface. Three major fault planes (Fault A, B, and C) are identified in Chiayi area. The fault A strikes N-S and dips to the west in listric shape of 65›X to 40›X. Eight earthquakes including the main shock and 7 aftershocks (M$_{L}$ $>$ 4) located on this fault plane all show a focal mechanism of reverse faulting and a nodal plane parallel to the fault plane. The aftershocks distributed in the northern study area allow us further identify another two nearly vertical fault planes, striking N80 ›XE (Fault B) and N80›XW (Fault C) respectively. Five focal solutions indicate they are pure strike-slip. Since the main shock is located at the bottom of the Fault A, we therefore interpret that the main shock caused by rupturing on the fault A and simultaneously triggered not only aftershocks on the same fault plane, but also the other two strike-slip faults in the north. Judging the spatial relationships of the subsurface structures derived from this study and surface geology, (1) Fault A may be related to the growth of the Hsiaomei Anticline; (2) Fault B and C to the Meishan fault.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 7200 SEISMOLOGY
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting