Evidence for a transient hydromechanical and frictional faulting response during the 2011 Mw 5.6 Prague, Oklahoma earthquake sequence

Mechanisms for the delayed triggering between the Mw 4.8 foreshock and Mw 5.6 main shock of the 2011 earthquake sequence near Prague, Oklahoma, USA were investigated using a coupled fluid flow and fault mechanics numerical model. Because the stress orientations, stress magnitudes, fault geometry, and earthquake source mechanisms at the Prague site have been well-characterized by previous studies, this particular earthquake sequence offered an opportunity to explore the range of physical processes and in-situ fault properties that might be consistent with the 20 hour delayed triggering effect observed at the site. Our numerical experiments suggest that an initial undrained response resulting from elastic stress transfer from the foreshock followed by transient fluid flow along the fault may have contributed to the earthquake nucleation process. The results of the numerical experiments were used to constrain fault compliance and fault transmissivity for the fault that hosted the Mw 5.6 event. Relatively compliant behavior in response to changes in normal stress, corresponding to Skempton pore pressure coefficients near 1, was consistent with the field observations. Fault transmissivity was estimated to range from 10−18 to 10−15 m3. This study has implications for understanding hydraulic properties, frictional properties, and faulting behavior of basement faults in Oklahoma that are large enough to host damaging earthquakes.