Data-Driven Two-Fault Modeling of the Mw 6.0 2008 Wells, Nevada Earthquake Suggests a Listric Fault Rupture

Structural fault complexity at depth affects seismic hazard, earthquake physics, and regional tectonic behavior, but constraining such complexity is challenging. We present earthquake source models of the February 21, 2008, Mw 6.0 Wells event that occurred in the Basin and Range in the western USA, suggesting the rupture of both the shallow and deep parts of a listric fault. We use a large data set including 150 local seismic waveforms from the USArray combined with high-quality Interferometric Synthetic Aperture Radar and teleseismic waveforms. Rather than imposing an a priori fault geometry in the source inversions, as is often done in the literature, we use a data-driven approach whereby all the faulting parameters and number of faults are determined by the data alone. We find a two-fault normal faulting solution comprising: (i) a shallow (centroid depth similar to 4.6 km) sub-event with Mw 5.3 and fault dip of similar to 77 degrees; and (ii) a deeper (centroid depth similar to 8.8 km), larger Mw 6.0 sub-event on a fault with shallower dip angle (similar to 41 degrees). Our preferred two-fault model is consistent with aftershocks and with the tectonics of the region. The local USArray waveforms used in the modeling are key to detect the rupture of both shallow and deep parts of the possible listric fault. The lack of such dense and uniform coverage of earthquakes in other regions on Earth may explain why the full seismic rupture of listric faults may have gone undetected in the past. Thus, earthquake slip on whole listric faults may be more common than previously thought.