Imaging the subsurface structure of the Chelungpu Fault using MT and RIP methods

Hsung-Hung Liang

Abstract

The reactivation of Chelungpu fault in Central Taiwan in 1999 resulted in the disastrous Chi-Chi earthquake. The Taiwan Chelungpu-fault Drilling Project conducted a 2-km drilling and provide useful data for examining the usefulness of the geophysical techniques.

We conducted an electric resistivity survey in Taichung area to investigate subsurface structure of the Chelungpu Fault. The survey consists of forty-nine MT soundings along a profile of 200 m in length and across the TCDP site. In addition, three electric resistivity image profilings were carried out in the northern Shihgang area where large surface rupture occured. In the study area the Toukoshan Fromation shows a resistivity of 800-4000 Ω-m in the upper part (50-1500 m deep), and 200-800Ω-m in the lower part, The Cholan Fromation and the Chinshui Shale have dominant ranges of resistivity of 40-100 and 8-60 Ω-m. The Kueichulin Formation exhibits a resistivity of 50-1000 Ω-m in the upper part and 100-150Ω-m in the lower part.

The Chelungpu fault is a complex fault system with width greater than 800 m near the ground surface. It consists of two main fault zones, the basal and the Chi-Chi fault zones, minor fractures and back thrust. The basal fault zone has an average east-dipping angle of about 35°. The Chi-Chi fault zone has an average east-dipping angle of about 37° with uneven fault plane as shown in resistivity structure.

Reference

Cheng, P. H., A. T. S. Lin, Y. I. Ger, and K. H. Chen., (2006) Resistivity structures of the Chelungpu fault in the Taichung area, Taiwan. Terr.Atmos.Ocean. Sci., Vol. 17, No. 3,547-561.

(Abstract) (Full text)

Cheng, P. H. (2000) Imaging the subsurface structure of the northern tip of the 1999 Chi-Chi earthquake fault in central Taiwan using the electric resistivity method. Terr.Atmos.Ocean. Sci., Vol. 11, No,3, 721-734.

(Abstract) (Full text)