Prepare for advanced analysis of reservoir-triggered seismicity, Koyna Dam, India

The Koyna dam in India is one of the world?s largest reservoirs (Figure 1) and experiences every year an abundance of earthquakes since it was first filled in 1962. This is caused by the annual increase and reduction of the waterlevel, changing the load a nd thereby the stress field. The earthquakes are large magnitude and killing (Mmax=6.3 killing ~200 persons in 1967). The very crude relation: Change in waterlevel causes increase in earthquake activity is understood through the recording of the larger ea rthquakes recorded in a conventional network configuration; however, in order to improve the understanding of the reservoir-triggered seismicity, it is of utterly importance to incorporate small earthquakes and microearthquakes. Since the small earthquake s are much more abundant, automatic localisation of the events is required. For more detailed understanding and potential correlation of the event characteristics with water level changes, the analysis of event source parameters, such as moment magnitude, source radius, corner frequency, radiated seismic energy and stress drop is inevitable. This can only be done with improved monitoring and data processing capabilities. The analysis of full moment tensors, i.e. an improved characterisation of the earthqu ake source type with respect to opening/closing and shear cracks is an important step forward in the understanding of the earthquake mechanism. Improved understanding of the reservoir-triggered seismicity might also improve the models for event forecastin g which will be an important goal that also reduces the earthquake risk. Within this establishment phase, NGRI and NORSAR will jointly analyse the data with new advanced software from NORSAR and evaluate strategies for further collaboration on earthquake hazard assessment.