3차원 토모그래피 기법을 이용한 분지구조의 가시화 - 대만지역 연구사례

Abstract

Spatial structural resolution in the uppermost few kilometers of the crust is always limited in any traditional seismic method including for example, 3-D tomographic inversion of travel time data, 3-D inversion of surface wave data from ambient ground noises between two-station pairs, and from forward modeling of seismic waveforms. Since velocity structure of the uppermost few kilometers of the earth is slower than that of the deeper reion, seismic rays in the upper crust are basically parallet to each other as they approaching to surface seismic station, thus poor structural resolution. By properly taking care of elevation differences between seismic station sites and estimating effect of lateral structural variations in the shallow crust, images of velocity sedimentary basins in the Taiwan region can be resolved by traditional 3-D tomographic inversion of seismic travel times. It is apparent that Pintung basin in southern Taiwan is characterized by the deepest sediments in Taiwan, corresponding to one of the largest gravity lows and positive travel time residuals. Other sedimentary basins in Taipei, Ilan, Xingchu, Taichung, and Chiayi-Tainan regions can also be imaged from this study. Relocated earthquakes using 3-D Vp and Vs struvtural models reveal that no earthquakes occurred inside any basin and seismicity associated with active fault is apparent, for example at Xinchu basin in t