Geothermal/Induced Seismicity Impact

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Geothermal Induced Seismicity Impact

Induced Seismicity Impact
Present, Potentially Affected

  • DOE-EA-1733 (Calpine Enhanced Geothermal Systems Project EA at Geysers Geothermal Area for Geothermal/Well Field)
  • DOE-EA-1759 (EA for Geothermal/Exploration at Southwest Alaska Regional Geothermal Energy Project Naknek, Alaska)
  • DOI-BLM-NV-W010-2012-0057-EA (EA for Well 15-12 Hydro-Stimulation at Brady Hot Springs Geothermal Area for Geothermal/Well Field)

Induced seismicity is when underground infrastructure, such as pipes and injection wells trigger seismic events that otherwise would not have occurred. The technique type of geothermal exploration and drilling used will determine the risk of induced seismic events. For instances Enhanced Geothermal Systems (EGS) is a more invasive geothermal thermal development technique that uses injection wells and heightens induced seismicity risks.

Geothermal infrastructure is built to withstand the highest magnitude of earthquake possible in the area. Specific tests and evaluations are conducted before site selection to ensure construction does not happen on an active fault line or has shallow shear-wave velocities beneath the selected site. The shear-wave velocity test measures ground motion impacts to buildings. The test results predict infrastructure resiliency and aids in natural and induced hazard analysis.

Induced Seismicity Impact Impacts & Mitigation

Well drilling can induce adverse project impacts. The following mitigation measures may decrease severe seismicity impacts.

EGS: These systems inject water and geothermal fluids to create an underground reservoir. This allows for areas with hot bedrock, but no water, to be used for geothermal energy development. EGS is often located near sites of naturally occurring earthquakes. Consequently, injecting and removing liquid from the ground impacts bedrock and induces seismicity. Mitigating these consequences starts with conducting proper geologic and tectonic plate evaluations. Site relocation could decrease potential risks too.

However, induced seismicity can still occur after a pumping cycle. Underground stress multiplies when a pumping cycle does not finish on time, or too much liquid is extracted. In the event that seismicity occurs after the pumping cycle and causes property damage to the nearby community, mitigation measures include providing appropriate compensation and community support.

Seismic risks: To unveil potential impacts, conduct evaluations on tectonic stress fields with earthquake focal instruments. Assess seismicity rates, the state of stress, and failure mechanisms. Knowing the state of stress can reveal where stress build-ups and releases happen and if they can be induced by EGS injection fluid. Locate prior datasets and seismic monitoring results to assess the structural framework of the proposed site. All of these tests can point to whether or not relocate a site or what type of technology to use to mitigate these risks. U.S. National Park Service-Geothermal Energy Webpage

Subsistence: This is the gradual process of land depression or sinking. Subsistence can occur along fault lines or near active volcanoes; in sedimentary rock basins that are filled with clay, sand, silt or gravel; or as a byproduct of EGS extraction and injection fluids. Soil composition can reveal properties prone to subsistence. In the event that EGS is the cause of subsistence, mitigation measures include decreasing the reservoir’s pore pressure to reinforce the reservoir’s walls.

Technology: Predicting induced seismicity is more complicated than predicting natural seismicity because those technical tools and datasets are not widespread. As seismic monitoring results become more accessible, site re-evaluation can happen to reduce the uncertainties of seismic activity and impacts. 3D Seismic is often used in determining the presence of oil and gas reservoirs, but can also be used for seismic exploration and forecasting. It uses acoustic energy to get an underground sound picture. This 3D image is loaded onto a computer where scientists can use different factors to simulate seismic events.

Public concern: Surrounding communities often have ‘high-perceived risks’ about seismic activity, when the ‘actual risk’ is low. While induced seismicity does occasionally happen, it is usually under 3.5 on the Richter scale. Only earthquakes above 3.5 are felt. Establishing linkages between the community and the geothermal industry clears up seismicity confusion and builds trust between the two parties. Office of Energy Efficiency and Renewable Energy-Geothermal Power Plants-Minimizing Land Use and Impact