Monitoring micro-earthquakes in a geothermal field

Abstract

Passive seismic technique is one of several geophysical methods used to understand structures in subsurface geology. This technique can be used in geothermal exploration to delineate faults in areas of geothermal activity, and to locate permeable zones within the geothermal system. During the exploitation of a geothermal system, measurements of microseismicity are useful to monitor the response of the system to fluid injection and production. Injection can increase the level of microseismicity in an area by increasing the pore pressure, and thereby reducing the effective stress. In this study, the discussion is mainly based on monitoring of microearthquakes in the Hellisheidi geothermal system, located in the Hengill volcanic system. The area is located at the triple junction of two spreading zones and a transform zone and is therefore both tectonically and seismically active.

The data set used in this report is a part of a larger dataset recorded by a local seismic network operated in the Hengill area by the Iceland GeoSurvey (ÍSOR), Uppsala University, MIT, Reykjavik University, and the Iceland Meteorological Office (IMO) from 2009-2013. In this report, data from a small swarm on April 25th, 2012, were analysed using SeisComP3. A brief overview of microseismic surveys undertaken in the Hanle-Gaggade area in Djibouti is presented, describing the relationship between microearthquakes and signs of geothermal activity in the area. Earthquakes concentrated near the fault systems are observed, confirming that the area is seismically active and a local seismic network would be recommended for monitoring