Variations of Soil Gases on the Active Chihshang Fault in a Plate Suture Zone, Eastern Taiwan

Ching-Chou Fu1, Tsanyao Frank Yang1, V. Walia2, J.-C. Lee3, J.-J. Dong4, T.-K. Liu1, C-H. Chen1 and C.-S. Hou5

1. Department of Geosciences, National Taiwan University, Taiwan2. National Center for Research on Earthquake Engineering, NARL, Taiwan3. Institute of Earth Sciences, Academia Sinica, Taiwan4. Institute of Applied Geology, National Central University, Taiwan5. Central Geological Survey, MOEA, Taiwan

Geological settingGeological setting

Lee et al. (2003)

Lee & Angelier Lee & Angelier (1993)(1993) Yu & Kou (2001)Yu & Kou (2001)

Creepmeters data

Lee et al. (2003)

Anomalies => yes !! fault and/or fracture !!no anomalies => may be or may be not !!

Fu et al. (2005)

Soil gases result

Seismic refection profile Chang (2008)

Combining the above-mentioned data

Configuration of automatic station at CS

Equipped with: Rn detector

Lee et al. (2006)

Conclusion The soil gas method is considered to be a suitable tool for the

exploration of buried faults and/or fractures, at least in Taiwan.

Some anomalous radon concentrations can be observed. These anomalies usually appeared a few days before the local earthquakes, which mainly occurred in eastern Taiwan.

The heavy rainfall seemed to trigger creeping in only a few day. This implies that the creep zone is probably shallow. It is worth to note that some of the anomalies could not be related with any earthquake events, and considered may be related to surface creeping of the fault in studied area.

Soil radon anomalies seem to be more useful related to the earthquake events. It is worthy to continuous monitor to further clarify the relationship between soil gas variations and regional crustal stress/strain in the area.