This project aims to improve our understanding of the mechanics of earthquake nucleation and triggering by relating earthquake occurrence to improved seismological and geodetic observations of transient stress changes at depth. The project is focused on the Geysers Geothermal Field in California that is one of the most active seismogenic zones in North America. The Geysers area is an ideal natural laboratory for studying temporal variations is the fact that there are a number of known tectonic and environmentally induced sources of stress change in the Geysers area. Over the past 35 years, it appears that steam withdrawal and fluid injection have induced earthquakes in previously aseismic areas. The production activities would cause physical changes in the geothermal reservoir. Together with EarthScope InSAR data, large volumes of high-quality continuous seismic data from dense local and regional seismic networks at the Geysers, California afford us the opportunity to construct a detailed view of the subsurface deformation sources and their variability in time.
The main component of the proposed studies is to map transient stress changes at seismogenic depths through the observation of temporal variations in the seismic wavefield, with additional constraints from InSAR measurements. The project explores temporal variations in seismic velocity and surface-wave anisotropy inferred from the three-component seismic noise wavefield, in order to characterize stress-induced changes in the crack properties (e.g., crack density and orientation) at depth. The other activity of this project examines spatiotemporal characteristics of remotely triggered earthquakes and seismic tremor. By integrating diverse data types, the results from this project provide an enhanced four-dimensional imaging of reservoir characterizations at the Geysers area.
In collaboration with Lawrence Berkeley National Laboratory (LBNL) and U.S. Geological Survey, we are implementing a data acquisition system for collecting complete continuous seismic data from the LBNL seismic network. Continuous seismic data that we collect are archived at the Northern California Earthquake Data Center (NCEDC). All data are available to the community over Internet through the NCEDC.
