Application of Surface Deformation and Induced Seismicity to Geothermal Operation and Exploration

The project demonstrated that InSAR is a cost-effective method of monitoring surface deformation over space and time significantly exceeding the capabilities of ground-based surveys. The measurements provided for the four study geothermal fields can be used as a reference point for future monitoring activities. This can greatly help geothermal operators and regulators in reservoir management and is highly recommended to continue in the future, especially in view of plans for additional geothermal developments.

The project used satellite data to detect land changes (deformation) in four geothermal fields in California (Coso, Salton Sea, North Brawley, and Heber). The research took place between 2017-2020. The project team applied a method known as interferometric synthetic aperture radar (InSAR) to detect and measure changes over time, at thousands of individual points. These consisted of vertical movements of the ground surface (sinking or rising, also known as subsidence or uplift, respectively) and horizontal displacements in the west-east direction. The observations agreed with data from ground-based surveys. They were also compared with seismicity resulting from geothermal industrial processes (induced) and occurring naturally (tectonic). Deformation modeling allowed the project team to connect surface deformation and fluid depletion from the geothermal operations.

Changes in the spatial patterns of surface deformation were associated with variations in production and injection. Subsidence at Coso and North Brawley decreased with decreasing production. Subsidence persisted in Salton Sea areas with steady energy production, while a geothermal development in the northeastern part of the field showed differences between the pre- and post-production periods. Both subsidence and uplift took place at Heber, changing with production and injection.

In some cases, induced seismicity clustered in areas of subsidence and correlated with fluid extraction rates. Tectonic earthquakes at Salton Sea (M5.1 in 2005) and North Brawley (M5.4 in 2012), and near Coso (M7.1 in 2019) caused distinct deformation signatures in the fields