Coseismic displacement and tectonic implication of 1951 Longitudinal Valley earthquake sequence, eastern Taiwan

摘要

The Longitudinal Valley Fault (LVF) in eastern Taiwan is an extremely active fault with 3–4 cm of displacements consumed each year along its length. The fault forms the suture zone between the Philippine Sea and Eurasian plates as a result of an oblique arc continental collision. From 22 October to 5 December 1951, four earthquakes (Ms > 7) shook the LVF. We used triangulation (from 1917 to 1921 to 1976–1978) and interseismic GPS (from 1990 to 1995) data to estimate coseismic displacements of the 1951 earthquake sequences. Coseismic displacement progressively decreases from north to south and the azimuth changes from north to NE, then to a NW direction. According to the inverted faulting mechanism, the Longitudinal Valley fault can be separated into three segments. Both the northern and central segments have a high dip angle to the east, but the southern segment is of listric fault geometry. The northern segment exhibits dominantly left lateral strike-slip faulting with reverse component, while the middle exhibits thrusting dominantly, and the southern segment exhibits thrusting with left-lateral motion associated with a smaller coseismic displacement. In addition, this three-segment deformation model can explain the pattern of recent crustal deformation along the LVF and Coastal Range.