| Abstract |
Seismic monitoring of the reservoir at BerlÌn geothermal field started in 1996. The objectives were to identify major seismic areas in and around the geothermal system, to monitor the natural and possible induced seismicity due to exploitation, to identify active faults and fluid circulation paths in the reservoir and to obtain information on the heat source. The seismic network has detected about 2800 shallow and low-magnitude local events within the geothermal field, mainly in the southern part, along the volcanic chain, believed is responsible for the heat source. Seismicity in the production and injection areas is related to pressure and pore pressure changes, respectively. It has been just a clear case of induced seismicity in a well stimulation operation at the TR10A well (Rivas and Torres,2003) a reinjection well at BerlÌn geothermal field. This is a unique case of controlled experiment. Seismicity within the BerlÌn area is thought to be related to the heat source of the system and fluid bearing fractures. Numerous micro earthquakes within injection and production areas, are thought to be partly induced by increasing pore pressure and fluid motion. No clear correlation is apparent between the monthly seismicity and extracted and injected mass. However, However, two earthquakes (Mw=7.6 and Mw = 6.6) occurred in January, 13th and February, 13th, 2001; two years after the start up of the two 28 Mw power stations, followed by a marked increase in seismic activity within the Berlin reservoir. The local seismic activity has been of low magnitude, indicating that the rocks have poor capacity to accumulate stress, releasing energy very often even with frequent low magnitude swarms. Therefore, it is believed that the seismic behavior in the field does not possess any threat to the environment, to the power station and surrounding communities. |