Self-potential studies in volcanic areas (4) - An attempt to estimate the in-situ value of the electrokinetic coupling coefficient

The large self-potential anomalies have been observed on many volcanoes. The anomalies are thought to be originated from the electrokinetic effect due to hydrothermal circulation within the volcanic edifices. The quantitative interpretation of the anomalies, therefore, provides an important information about the thermal process related with volcanic activities. It is important to know the in-situ value of the electrokinetic coupling coefficient for the quantitative interpretation of the anomalies. We made self-potential measurement in the Atosanupuri-Kawayu region as a field experiment to estimate the in-situ value of the coefficient. Subsurface structure and hydrothermal system, such as flow path, fluid volume flux, temperature, hydrouric permeability and so on, have been well studied by the hydrologists in this region. Combining these information with the observed self-potential field, we estimated the ζ-potential value within the range from -5 mV to -46 mV which is consistent with that of the laboratory experiment by Ishido and Mizutani (1981).