Mid-Continent Section

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Seismicity Rates in Oklahoma: A look at the seismicity increase of 2014


The seismicity rate observed during 2014 in Oklahoma was greater than any previous year. This includes years that had already seen a significant increase in the rate of seismicity. The record number of earthquakes occurred throughout 40 counties in Oklahoma. Of the 5,417 earthquakes reported in 2014, 967 were reported as felt to the Oklahoma Geological Survey (OGS) and/or the U.S. Geological Survey and 585 were of a local magnitude (ML) 3.0 or greater. Seismicity was concentrated in central and north-central Oklahoma with more than 43% of the earthquakes reported by the OGS located within Grant and Logan Counties. For 2014 the OGS catalog is complete to a minimum magnitude of 2.4ML with several known smaller earthquakes left un-located. Daily seismicity rates through time can be examined to determine when the increase in seismicity rates occurred. These seismicity rates also show that by the end of 2014, the daily rate of magnitude 3.0 or greater earthquakes is roughly equivalent to that of the annual average from 1980 to 2008. The Gutenberg-Richter relationship for the year normalized to a daily rate of earthquakes provides a relationship of a=3.215 ±0.241and b=1.217 ±0.022. We will place the seismicity observed within 2014 in the context of past seismicity in Oklahoma and will also examine whether 2015 seismicity is consistent with that observed during 2014.