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Simple kinematic modeling of particle motion along a curved fault similar to the ruptured Chelungpu fault, Taiwan, indicates a unique spatial slip pattern. Specifically, we find that the large convergent slip on the curve is a result of the minimum deformation scenario of the fault geometry and regional northwestern movement of the Philippine Sea Plate (PSP). The modeled deformation regime portrays an accumulation of deformation in the curved region, which coincides very well with a long-term observed NW-SE-trending seismogenic zone in the central Taiwan. This consistence suggests that the Chelungpu fault is a preexisting curved fault. This is further evidenced by geological and geophysical observations. Because the spatial slip pattern is locally and regionally tectonically controlled, it indicates that the rupture behavior of the Chi-Chi earthquake is repeatable. Better knowledge of the fault geometry and the regional plate motion may help us to predict the possible spatial slip distribution of large earthquakes. This discovery is important for avoiding large buildings and constructions near predicted large slip regions. [Copyright &y& Elsevier]

Abstract: The attenuation factor, Q, at a fault zone is an important parameter for understanding the physical properties. In this study, we investigated the Q value of the Chelungpu Fault, the main rupture of the Mw 7.6 Chi-Chi earthquake, using the 7-level TCDP borehole seismometer array (TCDPBHS). The TCDPBHS was deployed at depths from 945 to 1270m throughout the 1999 ruptured slip zone at 1111m. Three borehole seismometers (BHS1–BHS3) were placed in the hanging wall, and the remaining three (BHS5–BHS7) were placed in the foot wall, with BHS4 near the slip zone. The configuration allowed us to estimate the Q-structure of the recent ruptured fault zone. In this study, we estimated Q values between BHS1 and BHS4, Qs 1 (Qp 1) at the fault zone and between BHS4 to 2km in depth, Qs 4 (Qp 4) beneath the fault zone. We utilized two independent methods, the spectral ratio and spectral fitting analyses, for calculating the Q value of Qs 1 (Qp 1) in order to provide a reliability check. After analyzing 26 micro-events for Qs and 17 micro-events for Qp, we obtained consistent Q values from the two independent methods. The values of Qs 1 and Qp 1 were 21–22 and 27–35, respectively. The investigation for the value of Qs 4 was close to 45, and Qp 4 was 85. These Qp and Qs values are quiet consistent with observations obtained for the San Andreas Fault at the corresponding depth. A low Qs 1 value for the recent Chelungpu Fault zone suggests that this fault zone has been highly fractured. Qs values within the Chelungpu Fault, similar to those within the San Andreas Fault, suggest that the Q structure within the fault zone is sedimentary rock independent. However, the possible existence of fluids, fractures, and cracks dominates the attenuation feature in the fault zone. [Copyright &y& Elsevier]