DEFORMATION PATTERNS FROM STRAIN INVERSIONS ALONG THE EASTERN MARGIN OF THE OROGENIC SUTURE IN EASTERN TAIWAN

This research examines an eastern-dipping, 3D planar package of seismic events located along the Longitudinal Valley Fault System (LVFS) as a proxy for non-recoverable strain in the seismic source zone, to identify whether the package of events is representative of a relatively homogeneous oblique collision or if strain is spatially partitioned. The Longitudinal Valley region in Taiwan is one of the world's most tectonically active belts, an area of particularly high seismicity, and one of the few places where active suturing is occurring. The region is therefore a critical component in resolving the kinematics and evolution of Taiwan and may help contribute to an understanding of suture processes in general. The Longitudinal Valley fault (LVF) is slipping at a high rate, contributing to the rapid uplift of the Central Range to the west. Part of the fault is creeping aseismically at a high rate, but is still capable of coseismic rupture. The seismicity of this region extends to roughly 25-30 km and are predominantly composed of oblique-slip and thrusting focal mechanisms. Below this region, to a depth of about 50 km, strike-slip, oblique-slip, and extensional events dominate. The Yuli Belt—at the western edge of the LVFS—is an area of high pressure and low temperature rock which suggests a significant degree of uplift and possible transport along the convergent boundary. Exhumation rates from apatite fission track ages suggest a high exhumation rate of about 3-12 mm/year, in contrast to lower rates in the metamorphic core to the west. Competing methods for exhumation have been proposed: (1) forearc extraction (Sandmann et al.,2015) and (2) subduction channel flow (Brown et al.,2015). In this research, we carefully selected data clusters for inversion to identify the potential partitioning of oblique plate motion into spatially separate strike-slip and dip-slip components. Preliminary results indicate north to south heterogeneity in deformation. Reverse dip-slip motion dominates in the extreme north and south and trends toward oblique motion approaching central eastern Taiwan. The central latitude presents with a conspicuous region of apparent crustal thinning (e.g., subhorizontal extension) at shallow depths which corresponds with a lateral decrease is seismicity.