HR: 0800h
AN: T41B-1308    [Abstracts]
TI: Mechanical strengths of fault and its surrounding rocks on an active creeping fault at Chihshang, Eastern Taiwan: an approach of numerical modeling
AU: * Lee, J
EM: jclee@earth.sinica.edu.tw
AF: Academia Sinica, 128, Academica Road Sec. 2, Taipei, 115 Taiwan
AU: Chang, K
EM: kjchang@earth.sinica.edu.tw
AF: Academia Sinica, 128, Academica Road Sec. 2, Taipei, 115 Taiwan
AU: Huang, J
T41B-1308 AF: National Taiwan University, 1, Roosevelt Road Sec.4, Taipei, 106 Taiwan
AU: Lin, M
EM: mlin@ccms.ntu.edu.tw
AF: National Taiwan University, 1, Roosevelt Road Sec.4, Taipei, 106 Taiwan
AB: The Chihshang fault is one of the most active segments of the Longitudinal Valley Fault, the plate suture between the converging Philippine and Eurasian plates in eastern Taiwan. Two moderate earthquakes of M 6.2 and M 6.5 resulted from rupturing of the Chihshang fault with substantial surface ruptures, occurred in 1951 and 2003, respectively. In between the 50-year inter-seismic period, the Chihshang fault reveals a seasonal creeping behavior at a rapid rate of about 20-30 mm/yr, at least during the last 25 years with instrumental observation. Based on data from the Chinyuan geodetic network measured once or twice per year across the 150-m-wide fault zone since 1998, we deployed elastic and visco-elastic modeling in order to seek the fault geometry and the mechanical behaviors of the fault and its surround rocks, in the uppermost 120 m surface level. By searching best-fits for the least residual mean values, we obtained an optimal model with the following parameters: 1) 15-20 m of unconsolidated covered deposits for the surfacial locked zone, 2) 40°-50° of the fault dip angle, 3) cohesion of about 15 KPa and friction angle of 9°-12° for the mechanical strength of the fault, 4) Young­İs modulus of about 0.1-0.3 GPa for the surrounding rocks. These results show that the Chihshang fault at the Chinyuan site has a relatively week mechanical strength, which is consistent with the fact of continuously surface creep. However, creep occurred only in wet seasons indicates the mechanical strength of the fault might become significantly stronger during the dry season when no surface slip occurred. The optimal model also indicates that a gentle anticlinal fold developed in the hanging wall of the fault and that the slip on the fault plane decreases gradually from depth toward the surface with near-zero slip in the upper 15-20 m. It is worth to note that the surface ruptures on cultural feature, such as brittle concrete retaining walls, distributed in a rather wide fault zone, as interpreted as being due to a growing fold structure with a wide wavelength. It should be taken into consideration for mitigation against seismic hazards.
DE: 1200 GEODESY AND GRAVITY
DE: 7221 Paleoseismology (8036)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8107 Continental neotectonics (8002)
SC: Tectonophysics [T]
MN: Fall Meeting 2005