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| | Abstract | | Positive self-potential (SP) anomalies were observed on many active volcanoes and geothermal areas. It is generally thought to be caused by streaming potential associated with hydrothermal upflows. However, positive SP anomalies were observed on Kaimondake volcano where no sign of volcanic or hydrothermal activity is present.Zeta potential, a key factor of streaming potential generation, was measured for rock samples (11 samples) from the Kaimondake volcano by Hase et al. (2004). The results show that the zeta potentials of all samples are negative (-1 ~ -20 mV) in polarity and its variation seems to correspond to the variety of geological formations. In order to study the influence of inhomogeneous distribution of the zeta potential on the observed SP profile, we conducted numerical simulations by using the STAR reservoir simulator and EKP-postprocessor. As a result of the simulations, the specific SP profile on Kaimondake volcano can be interpreted to be created by simple groundwater flow with zeta potential variations on each geological rock stratum. This result implies that distribution of geological rock stratum can be estimated by using SP and zeta potential surveys if groundwater flow in the survey area is not complicated. |
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