Geophysical Research Letters Geophysical Research Letters 0094-8276 1944-8007 04 28 2015 42 8 10.1002/grl.v42.8 https://agupubs.onlinelibrary.wiley.com/toc/19448007/42/8 Earthquake hypocenters and focal mechanisms in central Oklahoma reveal a complex system of reactivated subsurface strike‐slip faulting D. E. McNamara U.S. Geological Survey Denver Colorado USA H. M. Benz U.S. Geological Survey Denver Colorado USA R. B. Herrmann Department of Earth and Atmospheric Sciences Saint Louis University St. Louis Missouri USA E. A. Bergman Global Seismological Services Golden Colorado USA P. Earle U.S. Geological Survey Denver Colorado USA A. Holland Oklahoma Geological Survey Norman Oklahoma USA R. Baldwin U.S. Geological Survey Denver Colorado USA A. Gassner U.S. Geological Survey Denver Colorado USA Abstract

The sharp increase in seismicity over a broad region of central Oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure. Since early 2010, numerous organizations have deployed temporary portable seismic stations in central Oklahoma in order to record the evolving seismicity. In this study, we apply a multiple‐event relocation method to produce a catalog of 3639 central Oklahoma earthquakes from late 2009 through 2014. Regional moment tensor (RMT) source parameters were determined for 195 of the largest and best recorded earthquakes. Combining RMT results with relocated seismicity enabled us to determine the length, depth, and style of faulting occurring on reactivated subsurface fault systems. Results show that the majority of earthquakes occur on near‐vertical, optimally oriented (NE‐SW and NW‐SE), strike‐slip faults in the shallow crystalline basement. These are necessary first‐order observations required to assess the potential hazards of individual faults in Oklahoma.

 Key Points

Oklahoma seismicity is occurring on faults capable of larger earthquakes

A high degree of potential earthquake hazard exists in Oklahoma

Reactivated structures in Oklahoma are optimally oriented for failure

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