Abstract

The 192-km-long Steens fault zone is the most prominent normal fault system in the northern Basin and Range province of western North America. We use trench mapping and radiometric dating to estimate displacements and timing of the last three surface-rupturing earthquakes (E1–E3) on the southern part of the fault south of Denio, Nevada. Coseismic displacements range from 1.1 to 2.2 ± 0.5 m, and radiometric ages indicate earthquake times of 11.5 ± 2.0 ka (E3), 6.1 ± 0.5 ka (E2), and 4.6 ± 1.0 ka (E1). These data yield recurrence intervals of 5.4 ± 2.1 k.y. between E3 and E2, 1.5 ± 1.1 k.y. between E2 and E1, and an elapsed time of 4.6 ± 1.0 k.y. since E1. The recurrence data yield variable interval slip rates (between 0.2 ± 0.22 and 1.5 ± 2.3 mm/yr), but slip rates averaged over the past ∼18 k.y. (0.24 ± 0.06 mm/year) are similar to long-term (8.5–12.5 Ma) slip rates (0.2 ± 0.1 mm/yr) measured a few kilometers to the north. We infer from the lack of significant topographic relief across the fault in Bog Hot Valley that the fault zone is propagating southward and may now be connected with a fault at the northwestern end of the Pine Forest Range. Displacements documented in the trench and a rupture length of 37 km indicate a history of three latest Quaternary earthquakes with magnitudes of M 6.6–7.1 on the southern part of the Steens fault zone.

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