Finite‐fault slip model of the 2011 M_w5.6 Prague, Oklahoma earthquake from regional waveforms

Abstract

The slip model for the 2011 M w 5.6 Prague, Oklahoma, earthquake is inferred using a linear least squares methodology. Waveforms of six aftershocks recorded at 21 regional stations are used as empirical Green's functions (EGFs). The solution indicates two large slip patches: one located around the hypocenter with a depth range of 3-5.5 km; the other located to the southwest of the epicenter with a depth range from 7.5 to 9.5 km. The total moment of the solution is estimated at 3.37 × 10 24 dyne cm (M w 5.65). The peak slip and average stress drop for the source at the hypocenter are 70 cm and 90 bars, respectively, approximately one half the values for the M w 5.8 2011 Mineral, Virginia, earthquake. The stress drop averaged over all areas of slip is 16 bars. The relatively low peak slip and stress drop may indicate an induced component in the origin of the Prague earthquake from deep fluid injection.

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

“…The sense of slip during both major events was predominantly strike‐slip which justified the use of vertical faults, but in reality geometrical effects would have contributed to the magnitude and shape of the stress changes along Fault B. Our fault model geometry was further justified by the inversion performed by Sun and Hartzell [], which placed the hypocenter of the nucleation site of Event B at 5 km depth (similar to the foreshock), and because the distribution of aftershocks on both faults existed at similar depths over the range of several kilometers. Using a two‐dimensional model allowed us to employ a spatial discretization along the faults that was fine enough to ensure numerically converged solutions for the earthquake nucleation process for values of the characteristic slip‐weakening distance as low as δ c =50 × 10 −6 m [ Lapusta , ; Rice and Ben‐Zion , ].…”

“…The hypocentral depths of Events A and B were recorded as 4.0 km and 7.0 km, respectively, although McNamara et al [] suggested that these depth estimations have large errors associated with them. The inversion performed by Sun and Hartzell [] suggested that slip on Fault B nucleated at a hypocentral depth of 5 km and was confined initially between depths of 4 and 6 km. In their analysis, Sumy et al [] estimated the rupture dimension for Event A as 2.8 km long by 2.9 km deep and for Event B as 8.3 km long by 5.4 km deep based on the distributions of aftershocks.…”

Resolving Horizontal Rupture Directivity of Moderate Crustal Earthquake in Sparse Network With Ambient Noise Location

“…The resolved rupture length is 4.4 km (Pnl), 7.6 km (Rayleigh wave), and 5.2 km (Love wave). In the slip distribution model (Sun & Hartzell, 2014), the largest slip patch is about 2-3 km southwest to the hypocenter. Figure 13 shows the rupture directivity derived from ambient noise location method, reference earthquake method, and aftershocks within 48 h. The distribution of early aftershocks extends for about 12 km, much longer than the typically value for a M w 5.7 event (McNamara et al, 2015;Somerville et al, 2001).…”

“…Due to the adoption of time shift in waveform fitting, the centroid depth derived by the CAP method is stable and less sensitive to the velocity model than other algorithms (Zhu & Helmberger, 1996). Sun and Hartzell (2014) inverted for the finite-fault slip model with regional waveforms, and the largest slip patch is located around the hypocenter with a depth range of 3.0-5.5 km. In the CAP inversion, for Pnl part, time window is 20 s long and the band-pass filter range is 0.05-0.25 Hz; for the surface waves, time window is 60 s long and the filter range is 0.02-0.1 Hz.…”

Efforts to monitor and characterize the recent increasing seismicity in central Oklahoma

“…In addition, earthquake source parameters determined by the USGS NEIC are used to determine long-term earthquake hazard throughout the United States (Petersen et al, 2014). The USGS is working on several fronts to understand better the mechanisms that drive the increase in earthquake rate and to estimate the changing earthquake hazard in Oklahoma (Hough, 2014;Keranen et al, 2014;Sumy et al, 2014;Sun and Hartzell, 2014;Ellsworth et al, 2015;McNamara et al, 2015;Petersen et al, 2015;H. M. Benz, R. McMahon, D. Aster, D. McNamara, and D. Harris, personal communication, 2015).…”