The 2015-2016 Earthquake Sequence in Cushing, Oklahoma driven by Coulomb
Stress Changes and Fluid Diffusions
Abstract
An M5 earthquake occurred on November 7th, 2016, near the city of
Cushing in Oklahoma, the largest crude oil storage site in the USA,
after nearby disposal wells had been shut-in responding to three M4+
earthquakes in 2015. In this study, we investigated the rupture process
of these M4+ events with finite fault model (FFM) inversions and
computed Coulomb stress changes during this Cushing sequence. We found
that the rupture processes of the four M4+ earthquakes are very complex,
and they appeared to trigger one another, as evidenced by the inverted
finite fault slip distribution and the calculated Coulomb stress change
after each event. The foreshocks of the first M4 earthquake are probably
triggered by Coulomb stress changes from previous earthquakes during
2014 and 2015 on unmapped faults several kilometers to the south. Fluid
diffusion likely drives the bilateral seismic migration of the Cushing
earthquake sequence after the foreshocks were triggered. In addition,
fluid injection from the northwest of Cushing fault might have gradually
increased the pore pressure on the Cushing fault, making the shallow
part of the fault critically stressed.