A magnetotelluric image at subduction zone: Taiwan

As part of an integrated project to map the 3-D structures beneath Taiwan, which is a typical example of arccontinental collision, broadband magnetotelluric (MT) data have been collected and analyzed at 20 sites uniformly covering the entire Taiwan. The determinant response of impedance tensor was calculated for inversion and the Occam's inversion which could generate smooth model was used for interpreting MT data at each site. A north dipping conductor, at a depth of approximately 10-20 km with resistivities lower than 100 ohm-m beneath the Island of Taiwan is undoubtedly the most significant feature obtained in this study. The depth are correlated well with the inferred depth of dehydration reactions from Suppe (1981) and the top of the aseismic lower crust observed by Wang (1994). We infer that this dipping conductor is associated with the upper surface of the subducting Philippine Sea plate. This finding also provides one more example to support the argument that conductivity anomalies are commonly associated with plate subduction.