Detection of aseismic slip and poroelastic reservoir deformation at the North Brawley Geothermal Field from 2009-2019

Kathryn Materna, Andrew J. Barbour, Junle Jiang, & Mariana Eneva

Under Review September 2021, SCEC Contribution #11715

The North Brawley Geothermal Field, located within the Brawley Seismic Zone of Southern California, presents a case study for understanding seismic hazards linked to fluid injection and geothermal energy extraction. An earthquake swarm near the geothermal field in 2012 included two earthquakes with magnitudes greater than 5 and was potentially preceded by a years-long aseismic slip transient. To better understand ground deformation around the geothermal field, including its evolution with time and its physical mechanisms, we analyze deformation before, during, and after the swarm using ground- and satellite-based geodetic techniques between 2009 and 2019. We integrate observations from GNSS, Sentinel-1, TerraSAR-X, UAVSAR, and leveling surveys into a single deformation history. Modeling of this new collection of observations provides evidence for 70% more pre-swarm aseismic slip than previously recognized at the North Brawley Geothermal Field from 2009-2012. During the 2012 Brawley swarm, our geodetic slip inversions closely match the results of seismic waveform inversions from the swarm events. After the 2012 swarm, surface deformation is dominated by poroelastic deformation of a shallow fluid reservoir at <1 km depth rather than fault slip. The deformation history and seismicity catalogs at North Brawley suggest a cessation of fault-related slip during the ~7 years after the 2012 earthquake swarm owing to both deep slow slip and shallow geothermal operations.

Key Words
aseismic slip, swarms, ground deformation, geothermal field, tectonic geodesy

Citation
Materna, K., Barbour, A. J., Jiang, J., & Eneva, M. (2021). Detection of aseismic slip and poroelastic reservoir deformation at the North Brawley Geothermal Field from 2009-2019. Journal of Geophysical Research - Solid Earth, (under review).


Related Projects & Working Groups
Stress and Deformation Over Time