The US Geological Survey added induced seismicity to its seismic-risk maps, the agency said Mar. 28, citing a sharp rise in earthquakes associated with wastewater disposal wells, especially in Oklahoma.
The revised maps came in the agency’s first 1-year outlook describing the potential of both natural and induced seismicity for central and eastern US (CEUS) states. Previously, USGS maps only identified natural earthquake hazards.
USGS scientists distinguished between human-induced and natural seismicity only in the CEUS. In the west, scientists categorized all earthquakes as natural. A different methodology was used for the CEUS than for the west.
Typically, emergency management officials and government building code committees use USGS seismic-risk maps.
“By including human-induced events, our assessment of earthquake hazards has significantly increased,” in some states, Mark Petersen, USGS national seismic hazard mapping project chief, said in a statement.
Some 7 million people in the CEUS live or work in areas threatened by induced seismicity, USGS said, although it stopped short of relating that earthquake exposure to potential severity of any damage.
Oklahoma was listed as having the greatest risk for hazards associated with induced seismicity. Other states listed in order of highest potential risk after Oklahoma were Kansas, Texas, Colorado, New Mexico, and Arkansas. Oklahoma and Texas have the largest populations exposed to induced earthquake potential.
Oklahoma’s response
“The good news is that we are already seeing a very positive response to those actions in the form of reduced seismic activity in the central and north central areas of Oklahoma,” the Oklahoma Oil & Gas Association said in a statement.
Saltwater injections into disposal wells peaked in 2014 at 1.8 million b/d, the Oklahoma Geological Survey said, adding that volume has been cut in half, which it attributed in part to lower oil prices.
The Oklahoma Corporation Commission (OCC) previously released two regional seismicity response plan covering thousands of miles and hundreds of disposal wells in central and western Oklahoma.
Dana Murphy, a commissioner with OCC, described the USGS earthquake hazard map as being another element demonstrating the need for the actions already taken by OCC to reduce the risk of induced earthquakes in Oklahoma.
“The OCC has taken more than 25 actions over the past 3 years, and the response will continue to evolve with the science and the research,” Murphy said.
Murphy noted that researchers across various states are working to develop a model to predict the risk of induced seismic risk for a given area.
To determine whether particular clusters of earthquakes were natural or induced, USGS said it relied on published literature and discussions with state officials and the scientific and earthquake engineering community.
USGS scientists said they considered whether an earthquake occurred near a wastewater disposal well and whether the well was active at the time these earthquakes occurred. If so, it was classified as an induced event.
Current research indicates the maximum magnitudes of induced earthquakes may be lower than for natural earthquakes, but many scientists suggest that induced earthquakes can trigger larger earthquakes on known or unknown faults.
In the CEUS, there may be thousands of faults that could rupture in a large earthquake. Induced earthquakes also tend to exhibit swarm-like behavior with more numerous and smaller earthquakes at shallower depths. USGS noted in its news release.
Contact Paula Dittrick at [email protected].
