Fault zone resistivity structure and monitoring at the Taiwan Chelungpu Drilling Project (TCDP)

Chih Wen Chiang, Martyn J. Unsworth, Chow Son Chen, Chien Chih Chen, Andrew Tien Shun Lin, Han Lun Hsu

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The Taiwan Chelungpu-fault drilling project (TCDP) has undertaken scientific drilling and directly sampled the sub-surface rupture of the 1999 Chi-Chi earthquake. Audio-magnetotelluric (AMT) measurements were used to investigate electrical resistivity structure at the TCDP site from 2004-2006. These data show a geoelectric strike direction of N15°E to N30°E. Inversion and forward modeling of the AMT data were used to generate a 1-D resistivity model that has a prominent low resistivity zone (< 10 ohm-m) between depths of 1100 and 1500 m. When combined with porosity measurements, the AMT measurements imply that the ground water has a resistivity of 0.55 ohm-m at the depth of the fault zone. Time variations in the measured AMT data were observed from 2004-2005 with maximum changes of 43% in apparent resistivity and 18° in phase. The change in apparent resistivity is greatest in the 1000 - 100 Hz frequency band. These frequencies are sensitive to the resistivity structure of the upper 500 m of the hanging wall of the Chelungpu Fault. The decrease in resistivity over time appears to be robust and could be caused by an increase in porosity and a re-distribution of the groundwater.

Original languageEnglish
Pages (from-to)473-479
Number of pages7
JournalTerrestrial, Atmospheric and Oceanic Sciences
Volume19
Issue number5
DOIs
StatePublished - Oct 2008

Keywords

  • Audio-magnetotelluric
  • Chelungpu fault
  • Geo-electrical strike
  • Resistivity structure
  • TCDP
  • Time variations

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