Double coupled faulting associated with the 2006 Mw=6.1 Peinan earthquake, Eastern Taiwan

Based on measurements of a dense geodetic network including 59 GPS stations and six leveling routes, we characterized the pre-, co- and post-seismic deformation of the 2006 Mw=6.1 Peinan earthquake in eastern Taiwan. The focal mechanism of the main shock and the distribution of the aftershocks indicated that the earthquake resulted from left-lateral strike-slip faulting with a NNE striking fault plane. However, the geodetic measurements showed that two conjugated strike faults appeared to simultaneously reactivate during the earthquake. In addition to the aforementioned NNE-striking fault, an E-W trending fault with right-lateral movement seemingly occurred co-seismically across the middle of the Peinanshan massif near the epicenter. Our half- space elastic dislocation modeling indicated that the slip distributions on the causative faults are far from homogeneous, in terms of slip amount and direction. In particular, the southern part of the NNE fault revealed a significant thrust component in addition to the left-lateral motion. Geologically, we interpret that the NNE-striking faulting represented a predominant left-lateral shear occurred along the eastern edge of the Central Range while colliding with the obliquely converging Luzon arc. As for the E-W trending faulting, it represented a transfer fault zone separating the Longitudinal Valley fault, the major plate boundary fault, into the northern Chihshang fault segment and the southern Luyeh and Lichi faults system. The pre-seismic measurements showed a pre- seismic creep in the northern part of the NNE-trending fault and an interesting back-slip with opposing movement in the southern part of the fault. We also observed that the earthquake triggered movements as aseismic creep and major aftershock rupturing along the nearby two major thrust faults, the Luyeh and Lichi fault, respectively.