| Title | Temporal Velocity Variations beneath the Coso Geothermal Field Observed using Seismic Double Difference Tomography of Compressional and Shear Wave Arrival Times |
|---|---|
| Authors | Seher, Tim; Haijiang Zhang; Fehler, Mike; Haiying Yu; Soukhovitskaya, Veronika; Commer, Michael; Newman, Gregory |
| Year | 2011 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Coso; geothermal; microearthquake; double difference tomography; Poisson’s ratio; time lapse monitoring; joint inversion |
| Abstract | Microseismic imaging can be an important tool for characterizing geothermal reservoirs. Since microseismic sources occur more or less continuously both due to the operations of a geothermal field and the naturally occurring background seismicity, passive seismic monitoring is well suited to quantify the temporal variations in the vicinity of a geothermal field. We use microseismic data recorded between 1996 and 2008 to determine the temporally varying seismic velocity of the Coso geothermal field. In this study we will apply the double difference tomography method to simultaneously locate a suite of microseismic events and determine the compressional and shear wave velocity as well as their ratio. In a first step, we apply traveltime tomography based on the observed microearthquake catalog for every single year between 1996 and 2008 to obtain a first model for the subsurface velocities. In the next step we will estimate differential traveltimes using a cross-correlation technique. This allows us to apply double-difference tomography to refine our velocity models separately for each year. The double-difference method uses relative arrival times of earthquakes measured at the same station, which allows a more precise determination of the relative locations of earthquakes. In a final step, we plan to analyze temporal deviations from a reference model integrating the whole dataset between 1996 and 2008. |