Hundreds of earthquakes per day: The 2014 Guthrie, Oklahoma, Earthquake Sequence

A remarkable increase in seismic activity in Oklahoma since 2009 has been shown
to correlate closely with enhanced hydrocarbon extraction and associated
wastewater disposal; 99% of this recent Oklahoma earthquake activity has
occurred within 15 km of a call II injection well (Ellsworth, 2013). In response
to this increase in seismic activity, the U.S. Geological Survey (USGS) partnered
with the Oklahoma Geological Survey (OGS) to exchange waveform data from
permanent and temporary seismic stations to improve the cataloging of
earthquake source parameters for a broad region of north-central Oklahoma. For
a particularly persistent earthquake sequence near Guthrie, Oklahoma, a
subspace detection method is applied to data from nearby seismic stations. This
approach documents the occurrence of hundreds of readily detectable, highly
similar, earthquakes per day, with rates occasionally exceeding 1000
earthquakes per day. Time-varying changes in b-value appear episodic,
suggesting a correlation with periods of reversible fault weakening and
associated failure.