Geophysical Constraints on the Crustal Architecture of the Transtensional Warm Springs Valley Fault Zone, Northern Walker Lane, Western Nevada, USA

• Published in: Journal of geophysical research. Solid earth 2021-10, Vol.126 (10), p.n/a
• Main Authors: Briggs, Rich W., Stephenson, William J., McBride, John H., Odum, Jackson K., Reitman, Nadine G., Gold, Ryan D.
• Format: Article
• Language: English
• Subjects: Depth; Depth profiling; Dipping; Escarpments; Fault lines; Fault zones; Faults; Geological faults; Geological hazards; Geophysics; Holocene; Pleistocene; Reflection; Resolution; Seismic activity; Seismic analysis; Seismic data; Seismic hazard; Seismic profiles; seismic reflection; Seismic reflection profiles; Seismic surveys; Seismological data; Slip; transtension; Valleys; Walker Lane
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2020JB020757

The Walker Lane is a zone of distributed transtension where normal faults are overprinted by strike‐slip motion. We use two newly acquired, high‐resolution seismic reflection profiles and a reprocessed Consortium for Continental Reflection Profiling (COCORP) deep crustal reflection profile to assess the subsurface geometry of the Holocene‐active, transtensional Warm Springs Valley fault zone (WSVFZ) near Reno, Nevada, USA. Our multiscale observations extend to 12 km depth and suggest that the WSVFZ is more complex in the subsurface than implied by late Pleistocene surface fault traces. Two 4‐km‐long high‐resolution profiles image to a depth of ∼2 km and reveal moderately dipping reflections and truncations, some of which project to mapped scarps formed in late Pleistocene surfaces. The shallow lines are collocated with COCORP profile NV 08 along ∼40°N latitude. Reanalysis of the COCORP data reveals previously unidentified coherent reflections to a depth of ∼12 km and a previously mapped ∼30° west‐dipping fault at 8–12 km. From these seismic profiles, the WSVFZ is not a simple, subvertical fault zone extending through the entire seismogenic crust. Instead, the reflections are consistent with a zone of steeply and moderately dipping faults that simplify and steepen with depth before intersecting a mid‐crustal, low‐angle (∼25–30°) fault. The complex fault geometry of the WSVFZ implies that crustal shear is accommodated by a mix of dipping and subvertical faults in the transtensional northern Walker Lane. If so, transtensional fault zones may present challenges to paleoseismic and geodetic studies and require careful treatment when included in seismic hazard analyses. Plain Language Summary We use seismic data to obtain underground images in an area where modern faults move sideways (strike‐slip) but this motion is overprinted on faults that formerly moved only up‐and‐down (normal). We find evidence that the faults are more complicated underground than they appear at the surface, and that the former up‐and‐down (normal) faults may move in a sideways (strike‐slip) sense today. Key Points Shallow seismic reflection and deep crustal imaging reveal the geometry of a transtensional fault zone The Warm Springs Valley fault zone comprises subvertical and dipping faults that appear to terminate against a low‐angle fault at ∼8 km depth Transtensional fault zones present unique challenges to paleoseismic and geodetic studies and require careful treatment in seismic haza