Host: Abstracts of Annual Meeting of the Geochemical Society of Japan
Pages 59-
Monitoring of groundwater chemistry in seismically-active regions has been carried out since the 1980s in Taiwan. Change in groundwater chemistry has been observed before earthquakes and is proposed as a precursor signal since the 1980s in Taiwan. However, the biweekly/monthly sampling interval was commonly performed, some short-term precursory anomalies may not be caught due to the low sampling frequency. We designed an automatic sampling apparatus for the retrieval and temporal analysis of water geochemistry. The device was composed of the syringes connected to glass bottles with the septum for collecting fluids each day, which was installed at the Chelungpu Fault Drilling Project (TCDP) drilling well in central Taiwan for observing the discharge of fluids. The stable isotope ratios for oxygen and hydrogen anomalies of ~ +0.6‰ and +2.0‰, respectively, relative to the local background measured in groundwater were observed as the potential seismic precursor, one month before the Nantou earthquake (M6.2) in central Taiwan. The findings could be explained by the mixture between the different chemical concentrations from groundwater and surrounding formations through water-rock interaction, which may be associated with pre-seismically induced changes of permeability or opening of preexisting micro-fractures along the fault zones due to high fluid pressure. We suggest that the geochemical anomaly in groundwater could be useful for future researching on the earthquake precursor.
