Paleoseismic Results from the Alpine Site, Wasatch Fault Zone: Timing and Displacement Data for Six Holocene Earthquakes at the Salt Lake City–Provo Segment Boundary

Research Article| October 02, 2018 Paleoseismic Results from the Alpine Site, Wasatch Fault Zone: Timing and Displacement Data for Six Holocene Earthquakes at the Salt Lake City–Provo Segment Boundary S. E. K. Bennett; S. E. K. Bennett aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.govdNow at Geology Minerals Energy and Geophysics Science Center, U.S. Geological Survey, Menlo Park, California 94025. Search for other works by this author on: GSW Google Scholar C. B. DuRoss; C. B. DuRoss bUtah Geological Survey, P.O. Box 146100, Salt Lake City, Utah 84114eNow at Geological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401. Search for other works by this author on: GSW Google Scholar R. D. Gold; R. D. Gold aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.gov Search for other works by this author on: GSW Google Scholar R. W. Briggs; R. W. Briggs aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.gov Search for other works by this author on: GSW Google Scholar S. F. Personius; S. F. Personius aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.gov Search for other works by this author on: GSW Google Scholar N. G. Reitman; N. G. Reitman aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.govfNow at Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado 80309. Search for other works by this author on: GSW Google Scholar J. R. Devore; J. R. Devore aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.gov Search for other works by this author on: GSW Google Scholar A. I. Hiscock; A. I. Hiscock bUtah Geological Survey, P.O. Box 146100, Salt Lake City, Utah 84114 Search for other works by this author on: GSW Google Scholar S. A. Mahan; S. A. Mahan cLuminescence Dating Laboratory, U.S. Geological Survey, Box 25046, MS 974, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar H. J. Gray; H. J. Gray cLuminescence Dating Laboratory, U.S. Geological Survey, Box 25046, MS 974, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar S. Gunnarson; S. Gunnarson cLuminescence Dating Laboratory, U.S. Geological Survey, Box 25046, MS 974, Denver, Colorado 80225gNow at University of Iceland ‐ Háskóli Íslands, Reykjavík, Iceland. Search for other works by this author on: GSW Google Scholar W. J. Stephenson; W. J. Stephenson aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.gov Search for other works by this author on: GSW Google Scholar E. Pettinger; E. Pettinger aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.gov Search for other works by this author on: GSW Google Scholar J. K. Odum J. K. Odum aGeological Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, sekbennett@usgs.gov Search for other works by this author on: GSW Google Scholar Bulletin of the Seismological Society of America (2018) 108 (6): 3202–3224. https://doi.org/10.1785/0120160358 Article history first online: 02 Oct 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation S. E. K. Bennett, C. B. DuRoss, R. D. Gold, R. W. Briggs, S. F. Personius, N. G. Reitman, J. R. Devore, A. I. Hiscock, S. A. Mahan, H. J. Gray, S. Gunnarson, W. J. Stephenson, E. Pettinger, J. K. Odum; Paleoseismic Results from the Alpine Site, Wasatch Fault Zone: Timing and Displacement Data for Six Holocene Earthquakes at the Salt Lake City–Provo Segment Boundary. Bulletin of the Seismological Society of America 2018;; 108 (6): 3202–3224. doi: https://doi.org/10.1785/0120160358 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract To improve the characterization of Holocene earthquakes on the Wasatch fault zone (WFZ), we conducted light detection and ranging (lidar)‐based neotectonic mapping and excavated a paleoseismic trench across an 8‐m‐high fault scarp near Alpine, Utah, located <1 km south of the boundary between the Salt Lake City and Provo segments (SLCS and PS). We document evidence for six paleoearthquakes (AL6–AL1) from scarp‐derived colluvial wedges and crosscutting relations. A ground‐penetrating radar survey across the scarp resolved fault‐zone width, but not paleoearthquake stratigraphy. Bayesian (OxCal) modeling of 13 radiocarbon and 13 optically stimulated luminescence ages indicates that six earthquakes occurred ∼6.2–0.4 ka⁠. Interseismic recurrence ranges from 0.2 to 1.8 ky (mean 1.2 ky). We estimate 6.5±0.7 m of cumulative vertical tectonic displacement across the ≥14‐m‐wide fault zone used near‐field observations of scarp‐derived colluvial‐wedge thicknesses, antithetic faulting, and graben backtilting. This is similar to our independent estimate of 6.5±0.5 m using far‐field observations of the offset ground surface and correlation of alluvial‐fan stratigraphy across the WFZ. These results suggest that colluvial‐wedge thickness at the Alpine site approximates one‐half the original west‐facing fault scarp height. Per‐event vertical displacements range from 0.8 to 1.2 m (mean 1.1 m), which we use to estimate surface rupture lengths that may exceed 50 km from earthquakes as large as moment magnitude (⁠Mw⁠) ∼7.0⁠. The late Holocene average vertical slip rate is 0.9 mm/yr (⁠0.7–1.2 mm/yr range). Earthquake frequency has increased in the past ∼1 ky⁠, whereas displacement per event has been similar for the past ∼6 ky⁠, suggesting that strain accumulation is not the sole factor that controls the frequency and size of earthquakes at the SLCS–PS segment boundary. These findings can be used for a more nuanced characterization of earthquakes at the SLCS–PS boundary and improve earthquake hazard assessments along the Wasatch Front. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.