3차원 지각 및 상부맨틀 Vp 와 Vs 모델 결정 및 검증

Abstract

A comparison of P-wave travel time residuals between local crust and anti-pole events reveals that lateral variation of upper crust contribute to most of the observed residuals. A successful understanding and quantification of upper crust structure is essential for a reliable determination of 3D crust and upper mantle veolcity structure. Synthetic P and S station corrections can be obtained from JHD analysis of the calculated travel times from local events via 3D model to stations. Similarities between the observed and the synthetic P and S station corrections provide the first validation that the resultant 3-D density model from which the expected gravity at sea level can be calculated. The observed and calculated Bouguer gravity anomaly can then be compared to further validate the closeness of the resultant 3-D models to the real earth. We applied the above approaches to the Taiwan region. Spatial patterns and lateral variations of gravity anomalies derived from the two independent geophysical data sets agree exceptionally well in most areas. All earthquakes in the catalog are relocated using the resultant 3-D models. Tectonic implications of the resultant 3-D models and relocated can thus be explored. The high mountains are characterized by deep root, ~55-60 km, and brittle active upper crust and ductile aseismic mid to lower crust. The Central Range is bounded by two high angle thrust faults extending from near surface to ~30km. The continental and oceaninc crust deformed across the north-south trending collision suture in eastern Taiwan beneath which crustal thickness is relatively thin, ~23 km. Thus, the excessive heat from the collision and the elevated upper mantle may play an important role in the tectonic evolution of the Taiwan region.