We propose to use GPS technology in the area of the Pawnee earthquake to measure slow movements of the ground caused by the earthquake that are expected to occur there during the next 1-2 years. One of the causes of these so-called ?post-seismic? movements after natural earthquakes is the readjustment of fluids around the fault to the new crustal stress field generated by the earthquake. The injection of wastewater in Oklahoma from oil production has increased from 5 to 10 times since 2009, and this increased injection rate is thought to have induced a concurrent 450% increase in the number of earthquakes in this state. The Pawnee earthquake is the largest historical event in Oklahoma and, if confirmed that it is induced, among the largest induced earthquakes to date worldwide. The proposed work will provide the first capture of the postseismic deformation field of an earthquake not associated with a seismically active plate boundary such as the existing in California, and if confirmed that it is induced, a human induced earthquake. Analysis of the post-seismic signal will contribute to understanding the role of fluid, and the injection of fluid, in both natural and possibly induced earthquakes, and guide development of strategies to mitigate damage from earthquakes induced by fluid injection.
We propose installing 8 geodetically monumented, Continuous GPS (CGPS) stations to perform post-seismic deformation measurements in the epicentral region of the 3 September 2016, M 5.8, Pawnee, Oklahoma earthquake. In addition to being intraplate, and the largest historical earthquake in Oklahoma, this event also occurred within a region experiencing an exponential increase in seismic activity since the start of 2009 that we think is related to a significant coincident increase in the rate of disposal by injection of wastewater from petroleum production. An earthquake this size should produce a measurable postseismic deformation signal over a period of a few years that can provide important information about the event and the properties and state of the crust and faults in the epicentral region. The CGPS measurements will complement seismic and other geophysical studies of this earthquake by providing data on post-seismic crustal deformation, especially the fluid poroelastic component, caused by the earthquake. Such data will be essential for modeling crustal and fault properties, potentially contribute to improving our understanding the role of fluids in the earthquake process, and reducing seismic hazard from induced earthquakes.
