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

Abstract

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 ∼4.6 km) sub‐event with Mw 5.3 and fault dip of ∼77°; and (ii) a deeper (centroid depth ∼8.8 km), larger Mw 6.0 sub‐event on a fault with shallower dip angle (∼41°). 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.

An Atypical Shallow Mw 5.3, 2021 Earthquake in the Western Corinth Rift (Greece)

“…The situation is similar to that in Figure 4 of Frietsch et al. (2021) who note that visual comparison of waveforms for single‐fault and two‐fault models is not very efficient when one of the subevents is significantly greater than the other. It means that our waveform data do not necessarily require the Sub1 but they allow for its presence at depth, which was strongly suggested by the hypocenter location.…”

“…surface, such as bends, relays, or jogs, vertical segmentation is particularly challenging. As pointed out by Frietsch et al (2021), distinguishing multiple subevents of down-dip segmented normal faults during moderate earthquakes is a difficult and understudied topic, important for seismic hazard assessments. Thus, the proposed two-segment faulting hypothesis must be critically examined as follows.…”

Systematic Comparison of InSAR and Seismic Source Models for Moderate‐Size Earthquakes in Western China: Implication to the Seismogenic Capacity of the Shallow Crust

“…Along with the 27% non‐DC component reported by the GCMT and USGS solutions, this event may simultaneously rupture both shallow and deep faults, while only the shallow portion produced measurable surface deformation. Another example is the 2008 Wells, Nevada earthquake that also had a listric fault rupture, as revealed by the joint inversion of seismic and InSAR data (Frietsch et al., 2021). To reveal more rupture details of moderate‐size earthquakes, we may need more near‐field seismic observations, together with the geodetic data to better constrain the source parameters.…”

Crustal Structure of the Western U.S. From Rayleigh and Love Wave Amplification Data

“…Seismic imaging plays a crucial role in probing the structure and composition of the Earth's crust, especially when combined with laboratory measurements of crustal rocks (e.g., Christensen & Mooney, 1995; Rudnick & Gao, 2014). Seismic images of the Earth's crust are also useful for seismic hazard assessment (e.g., by providing key input information for accurate ground motion simulations) and are crucial for accurate earthquake source modeling (e.g., Frietsch et al., 2021). Moreover, removing the effects of the heterogeneous crust on seismic measurements can help constrain mantle structure (e.g., Ferreira et al., 2010; Schaeffer & Lebedev, 2015).…”