Low footwall accelerations and variable surface rupture behavior on the Fort Sage Mountains fault, northeast California
Bulletin of the Seismological Society of America
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Abstract
The Fort Sage Mountains fault zone is a normal fault in the Walker Lane of the western Basin and Range that produced a small surface rupture (<20 cm) during an ML 5.6 earthquake in 1950. We investigate the paleoseismic history of the Fort Sage fault and find evidence for two paleoearthquakes with surface displacements much larger than those observed in 1950. Rupture of the Fort Sage fault ∼5.6 ka resulted in surface displacements of at least 0.8–1.5 m, implying earthquake moment magnitudes (Mw) of 6.7–7.1. An older rupture at ∼20.5 ka displaced the ground at least 1.5 m, implying an earthquake of Mw 6.8–7.1. A field of precariously balanced rocks (PBRs) is located less than 1 km from the surface‐rupture trace of this Holocene‐active normal fault. Ground‐motion prediction equations (GMPEs) predict peak ground accelerations (PGAs) of 0.2–0.3g for the 1950 rupture and 0.3–0.5g for the ∼5.6 ka paleoearthquake one kilometer from the fault‐surface trace, yet field tests indicate that the Fort Sage PBRs will be toppled by PGAs between 0.1–0.3g. We discuss the paleoseismic history of the Fort Sage fault in the context of the nearby PBRs, GMPEs, and probabilistic seismic hazard maps for extensional regimes. If the Fort Sage PBRs are older than the mid‐Holocene rupture on the Fort Sage fault zone, this implies that current GMPEs may overestimate near‐fault footwall ground motions at this site.
Suggested Citation
Briggs, R., Wesnousky, S.G., Brune, J.N., Purvance, M.D., Mahan, S., 2013, Low footwall accelerations and variable surface rupture behavior on the Fort Sage Mountains fault, northeast California: Bulletin of the Seismological Society of America, v. 103, no. 1, p. 157-168, https://doi.org/10.1785/0120110313.
ISSN: 1943-3573 (online)
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Low footwall accelerations and variable surface rupture behavior on the Fort Sage Mountains fault, northeast California |
| Series title | Bulletin of the Seismological Society of America |
| DOI | 10.1785/0120110313 |
| Volume | 103 |
| Issue | 1 |
| Publication Date | February 05, 2013 |
| Year Published | 2013 |
| Language | English |
| Publisher | Seismological Society of America |
| Contributing office(s) | Geologic Hazards Science Center |
| Description | 12 p. |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Bulletin of the Seismological Society of America |
| First page | 157 |
| Last page | 168 |
| Country | United States |
| State | California |
| Other Geospatial | Fort Sage Mountains Fault |