Class II Oil and Gas Wastewater Injection and Seismic Hazards in CA

By Kyle Ferrar, CA Program Coordinator, FracTracker Alliance Shake Ground Cover

In collaboration with the environmental advocacy groups Earthworks, Center for Biological Diversity, and Clean Water Action, The FracTracker Alliance has completed a proximity analysis of the locations of California’s Class II oil and gas wastewater injection wells to “recently” active fault zones in California. The results of the analysis can be found in the On Shaky Ground report, available for download at

Production of oil and natural gas results in a large and growing waste stream. Using current projections for oil development, the report projects a potential 9 trillion gallons of wastewater over the lifetime of the Monterey shale. In California the majority of wastewater is injected deep underground for disposal in wells deemed Class II wastewater injection.  The connection between seismic activity and underground injections of fluid has been well established, but with the current surge of shale resource development the occurrence of earthquakes in typically seismically inactive regions has increased, including a recent event in Ohio covered by the LA Times.   While both hydraulic fracturing and wastewater injection wells have been linked to the induction of seismic activity, the impacts of underground injection wells used for disposal are better documented and linked to larger magnitude earthquakes.

Therefore, while hydraulic fracturing of oil and gas wells has also been documented to induce seismic activity, the focus of this report is underground injection of waste fluids.

Active CA Faults

A spatial overview of the wastewater injection activity in California and recently active faults can be viewed in Figure 1, below.

Figure 1. California’s Faults and Wastewater Injection Wells. With this and all maps on this page, click on the arrows in the upper right hand corner of the map to view it fullscreen and to see the legend and more details.

The focus of the On Shaky Ground report outlines the relationship between does a thorough job reviewing the literature that shows how the underground injection of fluids induces seismic activity.  The proximity analysis of wastewater injection wells, conducted by The FracTracker Alliance, provides insight into the spatial distribution of the injection wells.  In addition, the report M7.8 earthquake along the San Andreas fault could cause 1,800 fatalities and nearly $213 billion in economic damages.2  To complement the report and provide further information on the potential impacts of earthquakes in California, FracTracker created the maps in Figure 2 and Figure 3.

Shaking Assessments

Figure 2 presents shaking amplification and shaking hazards assessments. The dataset is generated from seismic evaluations.  When there is an earthquake, the ground will amplify the seismic activity in certain ways.  The amount of amplification is typically dependent on distance to the earthquake event and the material that comprises the Earth’s crust.  Softer materials, such as areas of San Francisco built on landfills, will typically shake more than areas comprised of bedrock at the surface.  The type of shaking, whether it is low frequency or high frequency will also present varying hazards for different types of structures.  Low frequency shaking is more hazardous to larger buildings and infrastructure, whereas high frequency events can be more damaging to smaller structure such as single family houses.  Various assessments have been conducted throughout the state, the majority by the California Geological Survey and the United States Geological Survey.

Figure 2. California Earthquake Shaking Amplification and Class II Injection Wells

Landslide Hazards

Below, Figure 3. Southern California Landslide and Hazard Zones expands upon the map included in the On Shaky Ground report; during an earthquake liquefaction of soil and landslides represent some of the greatest hazards.  Liquefaction refers to the solid earth becoming “liquid-like”, whereas water-saturated, unconsolidated sediments are transformed into a substance that acts like a liquid, often in an earthquake. By undermining the foundations of infrastructure and buildings, liquefaction can cause serious damage. The highest hazard areas shown by the liquefaction hazard maps are concentrated in regions of man-made landfill, especially fill that was placed many decades ago in areas that were once submerged bay floor. Such areas along the Bay margins are found in San Francisco, Oakland and Alameda Island, as well as other places around San Francisco Bay. Other potentially hazardous areas include those along some of the larger streams, which produce the loose young soils that are particularly susceptible to liquefaction.  Liquefaction risks have been estimated by USGS and CGS specifically for the East Bay, multiple fault-slip scenarios for Santa Clara and for all the Bay Area in separate assessments.  There are not regional liquefaction risk estimate maps available outside of the bay area, although the CGS has identified regions of liquefaction and landslide hazards zones for the metropolitan areas surrounding the Bay Area and Los Angeles.  These maps outline the areas where liquefaction and landslides have occurred in the past and can be expected given a standard set of conservative assumptions, therefore there exist certain zoning codes and building requirements for infrastructure.

Figure 3. California Liquefaction/Landslide Hazards and Class II Injection Wells

Press Contacts

For more information about this report, please reach out to one of the following media contacts:

Alan Septoff
(202) 887-1872 x105
Patrick Sullivan
Center for Biological Diversity
(415) 632-5316
Andrew Grinberg
Clean Water Action
(415) 369-9172


  1. Arbelaez, J., Wolf, S., Grinberg, A. 2014. On Shaky Ground. Earthworks, Center for Biological Diversity, Clean Water Action. Available at
  2. Jones, L.M. et al. 2008. The Shakeout Scenario. USGS Open File Report 2008-1150. U.S. Department of the Interior, U.S. Geological Survey.