A study of the December 2016, The Geysers, CA earthquake using InSAR and GPS

Rachel L. Terry, Gareth J. Funning, & Michael Floyd

Published August 15, 2017, SCEC Contribution #7868, 2017 SCEC Annual Meeting Poster #097

The Geysers geothermal field in northern California, the largest of its kind in the world, has historically sustained high seismicity rates, connected to the production of steam from the over 400 geothermal wells in the area. In addition, the installation of wastewater injection pipelines to the field in 1997 and 2003 led to additional rises in seismicity as injected volumes increased tenfold over a period of a decade, making The Geysers an excellent laboratory for studying induced and triggered earthquakes.

In the morning of December 14th, 2016 a magnitude 5.0 earthquake occurred in the field, the largest in over 30 years. Particularly notable was the shallow hypocentral depth of the event, 1.5km, which is of similar depth to the injection wells in the field. The event was recorded at nearby continuous GPS stations, including two that we installed within The Geysers in 2012, indicating horizontal displacements of over 1 cm.

We find that this deformation is large enough to be identified by InSAR. We produce coseismic interferograms from SAR data acquired by the Sentinel-1 satellite on December 13th, 2016 and December 19th, 2016 using the ISCE software, and downsample the data using a quadtree decomposition algorithm. Using these data, and our GPS coseismic displacements, we model the earthquake source as a rectangular dislocation in an elastic half space, using a Markov Chain Monte Carlo to search for a distribution of plausible models.

Key Words
InSAR, GPS, Earthquake, Geothermal

Citation
Terry, R. L., Funning, G. J., & Floyd, M. (2017, 08). A study of the December 2016, The Geysers, CA earthquake using InSAR and GPS. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy