Seismic and Geomagnetic Observations at the Hydraulic Fracturing Test Site near Yakedake Volcano, Central Japan

Abstract

Hydraulic fracturing experiments of the Hot Dry Rock have been conducted at a site near Yakedake volcano (active volcano), central Japan, as one of the Sunshine project-New energy project by the Japanese Government since 1979. Making use of this opportunity, we made seismic and geomagnetic observations on the ground surface near the injection wells from 1980 to 1982. The following results were obtained:
1) Any change of microseismic activity around the test site was not detected from the daily frequency of the observed near microearthquakes.
2) Only a few seismic signals, which were presumably occurred beneath the test site, were detected during the injection of water.
3) The seismic waves passing through the newly formed fractured zone attenuate much more than those passing through the other paths. This shows a possibility to detect the newly formed fractured zone by the observation of seismic wave attenuation.
4) Q values of rock samples obtained from beneath the site were measured in the laboratory by the pulse transmission technique. As a result, the relation between Q value and porosity was obtained.
5) Any special geomagnetic variation near the injection well was not detected during the injection of water.