New Mexico Geological Society Annual Spring Meeting — Abstracts

Earthquake magnitude scales with the length of the ruptured fault plane. Regional seismic hazard assessments therefore require an understanding of how individual fault segments may link together to produce large earthquakes. Though fault segmentation’s impact on rupture has been explored along strike-slip faults, such as the San Andreas system in California, similar studies along normal faults are generally limited to the Wasatch fault in Utah (e.g. Duross 2016, Valentini et al., 2020). The Alamogordo fault is a segmented normal fault in the Tularosa Basin of south-central New Mexico with established seismogenic potential (Koning and Pazzaglia, 2002). A rupture along this fault would threaten critical infrastructure, such as the city of Alamogordo (population >30,000), White Sands Missile Range, and Holloman Air Force Base. Here we assess fault segmentation along the Alamogordo fault using a combination of remote sensing, field-based mapping, and geodynamic modeling techniques. Restricted access within the White Sands Missile Range has limited previous mapping efforts, but the release of new statewide lidar datasets allows us to conduct more detailed remote sensing-based neotectonic mapping. Our remote mapping efforts have increased the length of Quaternary rupture by >15 km at both ends of the fault. We have verified these remote mapping interpretations at three locations using high-resolution (1:5,000) neotectonic mapping at locations along the fault with differing geologic and geomorphic characteristics, including variations in basin depth, lithology, and fault geometry. We present one of those neotectonic maps here. These maps identify which Quaternary surfaces have been offset by the fault, allowing us to place an upper bracket on rupture timing. To assess different scenarios for segment linkage and long-term slip rates, we have integrated our updated fault geometries into the lithospheric dynamics code ASPECT. We compare these model results with slip rates derived from soil chronosequences that provide preliminary ages of offset surfaces. Future work will include the collection of cosmogenic nuclide geochronology datasets to validate soil chronosequence interpretations, allowing us to more precisely verify model results and the rupture history of the Alamogordo fault.

References:

1. DuRoss, C. B., S. F. Personius, A. J. Crone, S. S. Olig, M. D. Hylland, W. R. Lund, and D. P. Schwartz, 2016, Fault segmentation: New concepts from the Wasatch Fault Zone, Utah, USA, J. Geophys. Res. Solid Earth, 121, 1131–1157, doi:10.1002/ 2015JB012519.
2. Koning, D.J., and Pazzaglia, F. J., 2002, Paleoseismicity of the Alamogordo fault along the Sacramento Mountains, southern Rio Grande rift, New Mexico in: Lueth, V., Giles, K.A., Lucas, S.G., Kues, B.S., Myers, R.G., and Ulmer-Scholle, D., eds., New Mexico Geological Society 53rd Fall Field Conference Guidebook, Geology of White Sands, p. 107–119.
3. Valentini, A., C.B. DuRoss, E. H. Field, R. D. Gold, R. W. Briggs, F. Visini, and B. Pace, 2019, Relaxing segmentation on the Wasatch Fault Zone: Impact on seismic hazard, Bull. Seismol. Soc. Am. 110, 83-109, doi: 10.1785/0120190088