Geometry analysis on the distribution of seismicities recorded in the Nantou double earthquake sequences in 2013, central Taiwan

This study utilized the spatial and temporal distributions of the seismicities occurred in Nantou area, Taiwan to analyze the seimogenic structures for the purpose of understanding the faulting relationship that is the fundamental information for seismic risk evaluation. In the historical record, in 1916/1917 there was an double seismic event occurred at the similar location, which seriously damaged this mountain area. It became seismically quiescent until 2013, again occurred double seismic sequences led by two large earthquakes of M6.2 and 6.5 in March and June respectively. The geometries of above-mentioned two clusters for all aftershocks of ML > 2.0 are concordant with the focal mechanism derived from main shocks. Spatially they show two separated low angle east-dipping fault planes, implying two different asperities, but roughly distributed in similar attitude. According to previously published model, an active structure under the well-known decollement of Taiwan mountain belts is suggested by background seismicities. The proposed fault planes of this study may be its extension or connecting another one in the deeper depth.