CHARACTERISTICS OF MICROSEISMICITY IN THE DV11 INJECTION AREA, SOUTHEAST GEYSERS, CALIFORNIA

Abstract

Microearthquake (MEQ) occurrence surrounding the injection well DV11 in Unit 18 of the Southeast (SE) Geysers is investigated. Seismicity rates are compared to the injection rate, and to flow rates in nearby steam extraction wells, which were monitored during the Unit 18 Cooperative Injection Test in 1994 and 1995. The seismicity rate is seen to mirror both injection and production rates, although a time lag sometimes occurs. Waveform cross-correlation is performed for the MEQs in the DV11 area, and the events grouped into clusters based on waveform similarity. Relative location techniques applied to the events in two of these clusters show 7 events grouped into a volume of about 25 m in diameter, at an elevation of about -0.65 km msl and 5 events grouped into a vertically-oriented linear feature about 100 m in length, at about -1.8 km msl.