Seismological Evidence for the Crustal Exhumation Bounded by Lishan Fault in Central Taiwan

The characteristics of Lishan Fault or its existence has been under controversies in the past decade, leading to the arguments for the orogenesis of Taiwan. To better describe the subsurface structures in central Taiwan, we conducted a well-conditioned joint inversion of P-wave (Vp) and S-wave velocity (Vs) structures to explore detailed local structures and discontinuities in higher resolution. The results show that the Lishan Fault can be well delineated by a prominent velocity contrast subvertically. A high velocity body enclosed by Vp = 6.0 km/s is exhumed under the eastern Hsuehshan Range and right stop by the Lishan Fault on the east, demonstrating that the basement uplift in central Taiwan is bounded/controlled by the Lishan Fault, as a boundary fault. Parts of the high-velocity body also characterized with high Vp/Vs ratio area may indicate the mafic bodies related to the ancient rifting event. Furthermore, in 3D geometry, we found that this exhumed body that branches into the area in between two closely located Nantou earthquakes in 2013 may serve as a reason for the separating distribution of their aftershocks. Such findings could shed a light on the complicated orogenic tectonics and the hazard mitigation in the central Taiwan.

Key words: Lishan Fault, Nantou earthquakes, Basement uplift, Mountain building