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Through a proposed multiple-event analysis of teleseismic P-waves, this study investigated the radiated seismic energy and rupture process of the 2010 JiaSian earthquake. Results showed that the earthquake comprised at least two sub-events. The first sub-event was followed by the second sub-event, ˜1.7 s later. The entire source duration was 5.4 s. Let the two sub-events occur on the same fault plane with a strike of 304° and a dip of 28°; the first sub-event had a relatively smaller seismic moment (M0) and larger radiated seismic energy (Es) than the second sub-event, and this leads to the Es/M0 of the first sub-event larger than that of the second sub-event thus. This feature implies that the first sub-event probably had a higher static stress drop during faulting. The total M0 was estimated to be 2.17 x 1018 Nm, corresponding to Mw = 6.15, and the total Es was ˜2.91 x 1013 Nm, larger than that estimated only from a single source. Subsequently, the Es/M0 was approximately 1.3 x 10-5, lower than ordinary earthquakes. The low static stress drop was probably responsible for the low Es/M0. Overall, the 2010 JiaSian earthquake was characterized by a relatively low ES/M0 and low static stress drop, and then the partial stress drop model would be relatively appropriate to interpret its rupture process. [ABSTRACT FROM AUTHOR]

In the Taipei Metropolitan Area, there is a significant problem to be resolved: Can two major active faults, i.e., the Chinshan and Shanchiao faults fail simultaneously? The two faults are both normal faulting based upon recent observations. In order to explore this problem, the static stress transfer between the two faults has been analyzed. We compute the static Coulomb failure stress changes, ΔCFS, on a fault plane due to a failure of the neighboring fault. Numerical computations are conducted for the combinations of three different dip and rake angles of the two fault planes. Results show that the Chinshan fault can be more likely triggered by a failure of the Shanchiao fault. Rupture of a fault is more capable of triggering the neighboring fault, when the rake angle of the ruptured fault is toward than opposite to the striking direction of the to-be-triggered fault. [ABSTRACT FROM AUTHOR]

To monitor the fault activity in the Taipei area, a new broadband downhole seismic network comprised of three stations was established in the Taipei Basin over a period of three years, 2005 - 2007. The network geometry is a triangle with a station spacing of about 12 km covering the entire Taipei Basin. Each station has two holes of different depths containing modern instruments, including a low-gain broadband seismometer. The largest depth is 150 m. We report our first experience on the installation and operation of the broadband downhole seismic network in the Taipei Basin. Some representative records from the Pingtung earthquake doublet in December 2006 are shown here. Ground displacement during the Pingtung earthquake doublet can be recovered from the velocity records without the baseline corrections that are required for the acceleration records. Our network offers excellent data for accurate and effective characterization of seismic motion in the study area. Seismic data from this network will be shared with other research institutions in Taiwan and abroad for further research. [ABSTRACT FROM AUTHOR]

We characterize fault geometries for moderate and large earthquakes in and offshore southwest (SW) Taiwan. Stress orientation estimates suggest that the first shock of the Pingtung earthquake may be characterized by slab flexure. A region of predominately normal-faulting earthquakes is also defined. Using the maximum-likelihood Gutenberg-Richter relation, we find that the repeat times for magnitude, M ≧ 6.5 and M ≧ 7.0 earthquakes are approximately 30 and 80 years, respectively. By assuming a Gaussian probability distribution with a standard deviation of 0.4 the recurrence time, we estimate a 50% probability of an M ≧ 6.5 earthquake recurring in the next 30 years, while only a 20% probability of an M ≧ 7.0 in the next 50 years. To test the empirical relation that is currently being used to convert ML to seismic moment (M0), we test the well-defined energy to moment ratio (E/M0) for the region. We additionally utilize this method to identify the lack of slow-source earthquakes in several recent offshore events in Taiwan. [ABSTRACT FROM AUTHOR]