Urban geophysics: Tem mapping in the Taipei Basin, Taiwan

Abstract

In order to investigate the subsurface engineering geology of the Taipei Basin, Taiwan, more than 60 transient electro­magnetic (TEM) soundings were made. Coincident loop configuration with square transmitting loops 50 m on a side, were used for the survey. Qualitative interpretation of the apparent resistivity contour maps located the aquifer and geologic boundaries. Quantitative interpretation using nonlinear least-squares inversion further refined the aquifer boundaries of the Taipei Basin, and the resulting geoelectrical model adequately represented the known geology. In an attempt to map possible faults and to remove ambiguity from the model, during the inversion process the resistivities of the layers were kept within narrow limits across the entire area. Sharp depth discontinuities clearly displayed the known fault zones, reflecting some of the tectonic events of Taipei Basin. The TEM soundings provided information on the distribution of aquifers, sedimentary depositional environments, and the delineation of fault traces. The TEM method proved to be one of the most useful geophysical tools for urban geophysics.