The Nephi segment of the Wasatch fault zone (WFZ) comprises two fault strands, the northern and southern strands, which have evidence of recurrent late Holocene surface-faulting earthquakes. We excavated paleoseismic trenches across these strands to refine and expand their Holocene earthquake chronologies; improve estimates of earthquake recurrence, displacement, and fault slip rate; and assess whether the strands rupture separately or synchronously in large earthquakes. Paleoseismic data from the Spring Lake site expand the Holocene record of earthquakes on the northern strand: at least five to seven earthquakes ruptured the Spring Lake site at 0.9 ± 0.2 ka (2σ), 2.9 ± 0.7 ka, 4.0 ± 0.5 ka, 4.8 ± 0.8 ka, 5.7 ± 0.8 ka, 6.6 ± 0.7 ka, and 13.1 ± 4.0 ka, yielding a Holocene mean recurrence of ~1.2–1.5 kyr and vertical slip rate of ~0.5–0.8 mm/yr. Paleoseismic data from the North Creek site help refine the Holocene earthquake chronology for the southern strand: at least five earthquakes ruptured the North Creek site at 0.2 ± 0.1 ka (2σ), 1.2 ± 0.1 ka, 2.6 ± 0.9 ka, 4.0 ± 0.1 ka, and 4.7 ± 0.7 ka, yielding a mean recurrence of 1.1–1.3 kyr and vertical slip rate of ~1.9–2.0 mm/yr. We compare these Spring Lake and North Creek data with previous paleoseismic data for the Nephi segment and report late Holocene mean recurrence intervals of ~1.0–1.2 kyr for the northern strand and ~1.1–1.3 kyr for the southern strand. The northern and southern strands have similar late Holocene earthquake histories, which allow for models of both independent and synchronous rupture. However, considering the earthquake timing probabilities and per-event vertical displacements, we have the greatest confidence in the simultaneous rupture of the strands, including rupture of one strand with spillover rupture to the other. Ultimately, our results improve the surface-faulting earthquake history of the Nephi segment and enhance our understanding of how structural barriers influence normal-fault rupture.
Citation Information
Publication Year | 2017 |
---|---|
Title | Holocene surface-faulting earthquakes at the Spring Lake and North Creek Sites on the Wasatch Fault Zone: Evidence for complex rupture of the Nephi Segment |
Authors | Christopher Duross, Michael D. Hylland, Adam Hiscock, Stephen Personius, Richard W. Briggs, Ryan D. Gold, Gregg Beukelman, Geg N McDonald, Ben Erickson, Adam McKean, Steve Angster, Roselyn King, Anthony J. Crone, Shannon A. Mahan |
Publication Type | Report |
Publication Subtype | Other Government Series |
Index ID | 70189851 |
Record Source | USGS Publications Warehouse |
USGS Organization | Geologic Hazards Science Center |
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Ryan D Gold, Ph.D.
Director, Geologic Hazards Science Center
Shannon Mahan
Research Geologist, TRIGA Reactor System Administrator, Acting Deputy Center Director
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Ryan D Gold, Ph.D.
Director, Geologic Hazards Science CenterEmailPhoneShannon Mahan
Research Geologist, TRIGA Reactor System Administrator, Acting Deputy Center DirectorEmailPhone