Relationships of Seismic Source Scaling in the Taiwan Region

Abstract

Source scaling relationships are analyzed for the Taiwan region through the estimates of source parameters. Such estimated parameters include corner frequency, source dimension, stress drop, average slip and seismic moment. The ultimate goal of this study is to provide regional scaling laws on the above source parameters for the Taiwan region. The corner frequency and seismic moment are first estimated independently form strongmotion recordings after having been corrected for geomertrical spreading, high-frequency decay and anelastic attenuation. The results reveal that earthquakes in the Ilan-Hualien source area are mainly associated with the northward subduction of the Philippine Sea plate beneath the Eurasian plate. The stress drop values of earthquakes in this area are staticticaly smaller than those drop values of earthquakes in this area are statistically smaller than those occurring on Taiwan Island. This implies that earthquakes occurring on the island with shallow focal depth are most likely intra-plate events. In general, the stress drop of earthquake events in the Taiwan region shows an increasing trend with regard to the earthquake magnitudes. Based on the results of M6, the stress drop of earthquakes in the subduction zone is usually under 220 bars, while that of earthquakes on Taiwan Island is not greater than 290 bars. The empirical scaling laws for the source parameters of the northeast seismic zone are more reliably established, and thus are better results than those of the three other source areas in the Taiwan region. The use of Brune¡¦s source model tends to overestimate the corner frequency, and therefore underestimate the. radius of the source dimension. Accordingly, the stress drop and average slip are overestimated. As a result, the corner frequency, stress drop and average slip obtained in this study should be treated as upper-bound values, and the diameters of the source rupture area estimated should be considered lower-bound values of the rupture length for estimated should be considered lower-bound values of the rupture length for earthquake events in the Taiwan region.

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