Application of the self-potential method to geothermal exploration in Long Valley, California

Abstract

A self-potential survey made in the Long Valley caldera produced an anomaly derived from a dipolar source superimposed on potentials negative in polarity in relation to the area outside the caldera. The dipolar anomaly, consisting of negative and positive components differing amplitude by approximately I V, is centered over a resurgent dome in the west central part of the caldera. The exact nature of the potential source is unknown; however, electrofiltration processes caused by movement of heated groundwater that gives rise to streaming potentials are thought to be the principal cause of the dipolar anomaly. Diffusion potentials resulting from concentration differences between rising volcanic water and descending meteoric water may be responsible for the negative potentials measured within the caldera. Potential increases as high as l100 mV were observed across the perimeter of the caldera.

Repeated Self-Potential Profiling of Izu-Oshima Volcano, Japan

“…Each of the surveys covered an area of 50-100 km2 with survey lines about 100 km in total length and data sampling intervals around 100 m. SP anomalies of various types were recorded, and obvious anomalies of positive polarity were observed in several different areas: the Kutcharo caldera (Ishido, 1989) and the Nigorikawa caldera (Ishido, 1981) in Hokkaido, the Sumikawa and Okuaizu geothermal areas in the northern part of Honshu , and the Unzen-seibu (NEDO, 1988) and Kirishima (Ishido et al, 1990) geothermal areas in Kyushu. Most of these cases provided additional support for correlations reported in the 1970's between positive anomalies and high temperature upflow zones (Zohdy et al, 1973;Zablocki, 1976;Anderson and Johnson, 1976). Electrokinetic potential (streaming potential) generated by hydrothermal circulation is the most probable cause of these positive anomalies (Ishido, 1981;Ishido and Pritchett, 1996).…”

Investigation of novel geophysical techniques for monitoring CO₂ movement during sequestration. Final report, CRADA

“…Examples include positive anomalies of as much as 2300 mV in amplitude and about 1 km in width measured on Kilauea volcano, Hawaii by Zablocki (1976); a negative anomaly of about 200 mV amplitude and about 1 km in width at the northwest edge of Dunes thermal area (Combs and Wilt, 1976); a steepsided positive anomaly of about 30 mV amplitude and 2 km in width over the Mud Volcano area of Yellowstone National Park (Zohdy et al, 1973); a dipolar anomaly covering over 15 km and about 900 mV peak-to-peak amplitude over a postulated resurgent dome in Long Valley, California (Anderson and Johnson, 1976); a negative anomaly of about 60 mV amplitude and 3 km in width centered over the Leach Hot Springs area of Grass Valley (Corwin, 1976), a well-developed dipolar anomaly of about 160 mV peak-to-trough amplitude; and peak-to-trough distance of about 7 km at Cerro Prieto geothermal field in Baja California (Corwin et al ,1980;and Fitterman and Corwin, 1982); negative SP anomalies, down to -1700 mV, with high gradients (1.83 mV/m) on Mount Pelee volcano due to a hydrothermal system, and a positive SP anomaly, up to 200 mV caused by two active hot springs (Zlotnicki et al, 1998).…”

Self-potential surveys related to probable geothermal anomalies, Hualalai Volcano, Hawaii

“…Strong correlations between positive topographic gradients and negative self-potential fields produced by subsurface water (streaming potentials)* have been cited as a reasonable explanation for self-potential anomalies in Yellowstone Park (Zohdy and others, 1973), Long Valley Caldera, Calif. (Anderson and Johnson, 1976), and on Kilauea Volcano (Zablocki, 1976). …”