The US Geological Survey issued a report with preliminary outlines of models to predict severity of ground tremors in areas where sharp seismicity increases have been reported. It said the models ultimately aim to calculate how often earthquakes are expected to occur in the next year, and how hard the ground will likely shake as a result.
The report also identifies issues that must be resolved to develop a final hazard model, which is scheduled for release at yearend after the preliminary models have been examined, the US Department of the Interior agency said. These preliminary models should be considered experimental and not be used to make decisions, it emphasized.
A sharp increase in earthquake activity since 2009 in the eastern and central US has been linked to industrial operations that dispose of wastewater by injecting it into deep wells, USGS said. Although wastewater disposal potentially can trigger earthquakes, most wells do not produce tremors that can be felt, it said.
Many questions also have been raised about whether hydraulic fracturing used as part of unconventional oil and gas production also might be responsible, it added. USGS said its studies suggest that the actual fracing process only occasionally directly causes felt earthquakes.
"These earthquakes are occurring at a higher rate than ever before and pose a much greater risk to people living nearby," USGS National Seismic Hazard Modeling Project Chief Mark D. Petersen said Apr. 23 as the report was released. "USGS is developing methods that overcome the challenges in assessing seismic hazards in these regions in order to support decisions that help keep communities safe."
17 areas in 8 states
USGS said its scientists identified 17 areas within Alabama, Arkansas, Colorado, Kansas, New Mexico, Ohio, Oklahoma, and Texas where seismicity rates have been high since 2000 and have increased substantially since 2009. They developed the models by analyzing earthquakes in these zones and considering their rates, locations, maximum magnitude, and ground motions.
The agency released updated National Seismic Hazard Maps in 2014, which describe hazard levels for natural quakes. Those maps are used in building codes, insurance rates, emergency preparedness plans, and other applications. They forecast the likelihood of quakes over 50 years, which is a building's average lifetime.
New induced seismicity products display intensity of potential ground-shaking over a year because the induced activity can vary rapidly with time and is subject to commercial and policy decisions which could change at any point, USGS said.
Noting that the report looked at the central and eastern US, USGS said future research will incorporate data from western states as well.
