Re-Examining Source Parameters of the 2012 Wutai, Taiwan Earthquake

Abstract

On 26 February 2012, an inland ML 6.4 earthquake occurred near Wutai Township in Pingtung County, Taiwan and caused massive shaking in southern Taiwan. After the 2010 ML 6.4 Jiasian earthquake caused extensive damage in southern Taiwan, deep, complicated structures were revealed. This earthquake provided us an opportunity to further investigate related tectonic issues and hazard mitigation. Although the focal mechanisms of the Wutai earthquake from various institutes's readings were quite consistent, a large uncertainty was present with regard to focal depth. The relocated source parameters suggest a deeper depth of 32.3 km and a focal mechanism of a 326° strike, a 35° dip, and a 57° rake. Based on the tectonic seismic profile in southern Taiwan, the hypocenter of the Wutai earthquake is therefore likely located in the lower crust and implied that the deep blind fault system under the southwestern Central Range could even go deeper southward, revealing complicated thick-skinned tectonics. In addition, due to the abundance records of the P-wave first-motion polarities collected, we also tested the feasibility of searching the source depth by a polarity fitting for which we demonstrated several synthetic tests and showed its strength. In applying the polarity fitting method to the real case of Wutai earthquake, the results indicated that this approach may be affected by the uncertainty of the epicenter sensitively. However, the application showed the potential that a large number of polarity data existing in earthquake catalog does not only dedicate to determine the focal mechanisms conventionally but may also contribute to the source location in the future.