Stress heterogeneity as a driver of aseismic slip during the 2011 Prague, Oklahoma aftershock sequence

The interaction of aseismic and seismic slip before and after an earthquake is fundamental for both earthquake nucleation and postseismic stress relaxation. However, it can be difficult to determine where and when aseismic slip occurs within the seismogenic zone because geodetic techniques are limited to detecting small slip at or near the surface. Here, we use repeating earthquakes as a proxy for aseismic slip during the 2011 Prague, Oklahoma earthquake sequence. We identify repeating events in both the basement and the Arbuckle formation by cross correlating waveforms with a 1-25 Hz bandpass filter using an average cross correlation value of at least 95% at three stations. Repeating earthquakes are recorded immediately after the November 6 Mw 5.7 and continue for at least two months. We find that areas of repeating earthquakes are co-located both in time and in space with areas of dense aftershocks. We interpret this as evidence that aftershocks are being driven by afterslip in the immediate vicinity. We highlight three geologically interesting groups of repeating earthquake families within the Prague sequence. Repeating earthquakes in the Arbuckle formation are co-located with the intersection of the three main faults in the area. The two deeper areas of repeating earthquakes occur at the intersections of the foreshock-mainshock faults and the mainshock-aftershock faults. Helmstetter and Shaw (2009) outlined how areas of high stress heterogeneity can have afterslip whether or not the material is velocity strengthening or weakening. We interpret our findings as evidence that areas of high stress heterogeneity, such as at fault intersections, allow for afterslip. This has implications for how stress is transferred post-seismically.