Oklahoma is No. 1 in ‘16 for number of earthquakes

Oklahoma has the highest potential for earthquake damage in 2016, according to a new report from the United State Geological Society.

For the first time, new USGS maps identify potential ground-shaking hazards from both human-induced and natural earthquakes. In the past, USGS maps only identified natural earthquake hazards.

The most significant hazards from induced seismicity are in six states, listed in order from highest to lowest potential hazard: Oklahoma, Kansas, Texas, Colorado, New Mexico and Arkansas. Oklahoma and Texas have the largest populations exposed to induced earthquakes.

“By including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the United States,” said Mark Petersen, Chief of the USGS National Seismic Hazard Mapping Project. “This research also shows that much more of the nation faces a significant chance of having damaging earthquakes over the next year, whether natural or human-induced.

“In the past five years, the USGS has documented high shaking and damage in areas of these six states, mostly from induced earthquakes. Furthermore, the USGS Did You Feel It? website has archived tens of thousands of reports from the public who experienced shaking in those states, including about 1,500 reports of strong shaking or damage.”

This is also the first one-year outlook for the nation’s earthquake hazards, and is a supplement to existing USGS assessments that provide a 50-year forecast.

The central United States has undergone the most dramatic increase in seismicity over the past six years. From 1973 to 2008, there was an average of 24 earthquakes of magnitude 3.0 and larger per year. From 2009 to 2015, the rate steadily increased, averaging 318 per year and peaking in 2015 with 1,010 earthquakes. Through mid-March in 2016, there have been 226 earthquakes of magnitude 3.0 and larger in the central U.S. region. To date, the largest earthquake located near several active injection wells was a magnitude 5.6 in 2011 near Prague, Oklahoma.

The report shows that approximately 7 million people live and work in areas of the central and eastern United States (CEUS) with potential for damaging shaking from induced seismicity. Within a few portions of the CEUS, the chance of damage from all types of earthquakes is similar to that of natural earthquakes in high-hazard areas of California.

USGS claims that induced earthquakes are triggered by human activities, with wastewater disposal being the primary cause for recent events in many areas of the CEUS. Wastewater from oil and gas production operations can be disposed of by injecting it into deep underground wells, below aquifers that provide drinking water.

USGS scientists only distinguished between human-induced and natural seismicity in the Central United States. In the west, scientists categorized all earthquakes as natural. Scientists also used a different methodology in looking at the CEUS compared to the west.

USGS scientists identified 21 areas with increased rates of induced seismicity. Induced earthquakes have occurred within small areas of Alabama and Ohio but a recent decrease in induced earthquake activity has resulted in a lower hazard forecast in these states for the next year.

In other areas of Alabama and small parts of Mississippi, there has been an increase in activity, and scientists are still investigating whether those events were induced or natural.

Building code committees are still determining whether it is appropriate to treat induced earthquakes in building code revisions, in part because induced seismicity changes on short time scales compared to the years it takes for building codes to be updated, reviewed and adopted.

While there are some areas of induced earthquakes in the western U.S., they don’t significantly change the regional hazard level compared to the much more abundant natural earthquakes. Therefore scientists just considered the historical catalog in the western United States and did not separate natural from induced earthquakes. Future research could take a more detailed look at induced seismicity in the west, including in California at The Geysers, Brawley or the Los Angeles Basin.

The USGS published a study in 2014 that only considered natural earthquakes. The largest changes in this new report are primarily due to hazards from induced earthquakes, but the calculations also consider updated forecasts for natural earthquakes since the previous hazard map was released. For example, the New Madrid Seismic Zone near Memphis has experienced a higher rate of natural earthquakes in the past two years, leading to a slightly higher hazard potential in small portions of Arkansas, Missouri, Illinois, Kentucky and Tennessee.

Wastewater disposal is thought to be the primary reason for the recent increase in earthquakes in the Central United States, according to the report.

While most injection wells are not associated with earthquakes, some other wells have been implicated in published scientific studies, and many states are now regulating wastewater injection in order to limit earthquake hazards.

Many questions have been raised about hydraulic fracturing—commonly referred to as “fracking”—and USGS studies suggest that this process is only rarely the cause of felt earthquakes.

To determine whether particular clusters of earthquakes were natural or induced, the USGS relied on published literature and discussions with state officials and the scientific and earthquake engineering community. Scientists looked at factors such as 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 that 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 Central United States, 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. These factors were taken into account in the analysis.

“We are using the best available data and principles to determine when, where and how strong the ground could shake from induced earthquakes,” said Petersen. “Of course there is a level of uncertainty associated with this and all hazard maps, as we are still learning about their behavior and can only forecast with probability – instead of predict with certainty – where earthquakes are likely to occur in the future. Testing these maps after a year will be important in validating and improving the models.”

Governor Mary Fallin said the USGS map illustrates why action taken earlier this year by the Oklahoma Corporation Commission (OCC) was necessary.

Researchers say the state’s rise in earthquakes is caused by the disposal of produced saltwater deep into the Arbuckle formation. The OCC, which has constitutional authority over oil and natural gas activity in the state, is following the recommendation of researchers and is continuing to work with operators to significantly reduce the overall disposal of produced water into the area of seismic interest within the Arbuckle formation area to 40 percent below the 2014 total.

The OCC last month issued a wide-ranging directive to saltwater disposal well operators in areas experiencing earthquakes. In the past year, regulators have issued more than a dozen directives to disposal well operators to limit activity or shut down in areas of earthquakes.

“Recent declines in produced wastewater disposal in Oklahoma are not reflected in the USGS map,” Fallin said. “This gives us even a stronger base in going forward and gives state regulators further justification for what they are doing.”

The USGS report, which used earthquake data from 2015, states that some places in Oklahoma may experience damage if the induced seismicity continues unabated.

“Oklahoma remains committed to doing whatever is necessary to reduce seismicity in the state. The report supports the actions that we are taking,” said Fallin, who in 2014 formed the Coordinating Council on Seismic Activity, which organizes state resources and related activities to address Oklahoma’s earthquakes.

Fallin asked Department of Emergency Management Director Albert Ashwood to lead a statewide working group to develop an earthquake response plan.

Ashwood and several agency directors held their first meeting last week.

“In Oklahoma, we recognize the importance of being prepared for all types of disasters that could affect the state, including earthquakes,” Ashwood said. “The Oklahoma Department of Emergency Management is reviewing the report released by the United States Geological Survey to determine how it may aid our catastrophic earthquake planning efforts.”

Oklahoma Energy and Environment Secretary Michael Teague said the USGS report highlights why action has been taken to address induced seismic risk in the state of Oklahoma.