Cumulative number of M ≥ 2.7 earthquakes in the central and eastern United States (CEUS) and five select zones of induced seismicity since 1980.

Hazard Estimation

The USGS National Seismic Hazard Model (NSHM) forecasts earthquake hazard, or the potential strength and frequency of ground shaking from future earthquakes, in the continental United States. The USGS releases a forecast about every six years, the last one was released in 2014. The forecasts are used in the design of buildings, bridges, highways, and other structures. They also provide critical information about areas of higher earthquake hazard for use by governmental disaster management agencies, industry, and the public for use in developing earthquake risk reduction plans and actions.

In previous NSHM forecasts, earthquakes that were attributed to human activity, including induced earthquakes from underground fluid injection or extraction, were not included. However, because of the recent increase in induced earthquakes in some areas of the central and eastern United States (CEUS) (e.g., Oklahoma) (Ellsworth, 2013) (Figure 1) and because the largest induced earthquakes have caused damage to buildings and other structures, induced earthquakes now need to be considered. Most induced earthquakes in the CEUS are thought to be caused by deep wastewater-disposal related to industrial activity (Andrews and Holland, 2015).

One-Year Forecasts

Chance of damage forecasted from an earthquake during 2016.

In March 2016, the USGS released its first induced earthquake hazard model, the 2016 One-Year Seismic Hazard Forecast for the CEUS from Induced and Natural Earthquakes. This model forecasted the strength and frequency of potential ground shaking from future induced and natural earthquakes for a one-year period, based primarily on earthquake data from the previous year (Figure 2). Areas of high induced earthquake hazard were identified in Oklahoma-southern Kansas, the Raton Basin (CO/NM border), north-central Texas, and north-central Arkansas. Near some areas of these active induced earthquakes, hazard is higher than in the 2014 NSHM by more than a factor of 3 and is similar to the chance of damage caused by natural earthquakes at sites in parts of California.

Chance of damage forecasted from an earthquake during 2016.

In March 2017, the USGS released an updated induced earthquake forecast for the CEUS for 2017. The 2017 one-year forecast uses the same earthquake hazard model and methodology as the 2016 one-year forecast, but incorporates an updated earthquake catalog that includes earthquakes from 2016 (Figure 3). The 2017 forecasted earthquake rates are lower in regions of induced earthquakes due to lower rates of earthquakes in 2016 compared to 2015, which may be related to decreased wastewater injection, caused by regulatory actions or by a decrease in unconventional oil and gas production. Nevertheless, the 2017 forecasted earthquake hazard is still significantly elevated in areas of the CEUS compared to the earthquake hazard calculated from only natural earthquakes in the 2014 NSHM.

Continuing Research

Current research activities include: development of new ground motion models (GMMs) specifically for induced earthquakes, analysis of catalog statistics, assessment of differences in induced and natural earthquake sources, estimation of potential induced earthquake magnitudes, consideration of alternative seismic rate models that are constrained by physics, and tests of models to identify parameters are all areas where research could improve the methodology. The USGS welcomes feedback from industry, academia, and users of the forecasts as this work continues.

References