Coloumb Stress Modeling of the 2011 M5.7 Oklahoma Earthquake Sequence

On 6 November 2011, a M5.7 earthquake ruptured a ~N55E-striking trend near the Wilzetta fault in Prague, Oklahoma. This earthquake was preceded by a M5.0 foreshock that occurred on 5 November 2011 and followed by a M5.0 aftershock that occurred on 8 November 2011. Three broadband seismometers were deployed following the M5.0 foreshock, and an additional seven broadband, eight short-period, and five strong-motion seismometers were installed following the mainshock, as part of a OU/PASSCAL-RAMP experiment. In addition, ten USGS stations were deployed in an approximately 100 km long linear array east of the mainshock epicenter. Using these temporary stations, approximately 700 events were recorded in the twelve hours leading up to the mainshock. The M5.7 event was followed by an active aftershock sequence and we manually detected aftershocks in the hours and days following the mainshock. Approximately 1000 events are located using manually picked arrivals and a 1D velocity model. Here, we use Coulomb 3 (Toda et al., 2011) to investigate the local Coulomb stress changes due to the M5.0 foreshock, M5.7 mainshock, and M5.0 aftershock. The foreshocks and aftershocks located within the first few hours surrounding the mainshock suggest very active faulting, with events defining three near-vertical fault planes. The planes defined by the seismicity of the foreshock and mainshock strike 34° and 55°, consistent with the range of strikes within the Wilzetta fault zone. The M5.0 aftershock appears to have occurred on a plane striking nearly 90°, clearly distinct from structures that were previously mapped. We first examine whether the stress change induced by the M5.0 foreshock increases the stress at the hypocentral location of the subsequent mainshock. Similarly, we determine the combined stress change from the foreshock and mainshock at the hypocentral location of the largest aftershock. Then, we compare the spatial distribution of earthquake activity after each of the three primary events to the Coulomb stress changes imposed on fault orientations inferred from aftershock focal mechanisms. These results will improve our understanding of earthquake interaction and triggering in this intraplate region.