Seismic Monitoring During a Cold Water Injection Experiment, Wairakei Field Geothermal Preliminary Results

Abstract

A microearthquake survey showed that induced seismic activity occurred during cold water injection tests at Wairakei Geothermal Field. Over a six week period more than 120 microearthquakes were recorded; 90 of these occurred during the nine days of injection tests. N o simple correlation between the occurrence of seismic activity and rate of injection, well head or step increases in injectivity was observed. Nineteen microearthquakes were located ; their epicentres having a roughly elliptical distribution with the major axis in a NE-SW direction. Epicentres were up to 3.3 km from the injection site, the more distant occurring outside the field boundary. The observed value of 0.6 forth e microearthquakes is typical of normal tectonic earthquakes.