Abstract

Deformation across three major fault strands within the Lake Tahoe basin has been mapped by using a novel combination of high-resolution seismic chirp, airborne laser-and acoustic-multibeam–derived bathymetry, and deep- and shallow-water sediment cores. Submerged erosional terraces of late Pleistocene age (19.2 ± 1.8 ka) record vertical deformation across fault strands that ranges between 10 and 15 m; offset of 10 m is observed across the southern part of the West Tahoe fault. Avalanche deposits from the catastrophic McKinney Bay slide (ca. 60 ka) are offset across the Stateline fault by at least 21–25 m. The submerged shoreline terraces and debris avalanche provide marker beds with which to constrain the extensional history of the region for the past 60 k.y. This history is then used to assess the future seismic hazard of the region. Data on deformation across these two important marker beds, combined with chronological control from 14C and optically stimulated luminescence measurements, yield an estimate of extension across the Lake Tahoe basin that is 0.4–0.5 mm/yr. On the basis of these measurements, there exists the potential for a large, seiche wave–generating M7 earthquake every ∼3 k.y. Late Pleistocene and Holocene vertical deformation rates within the Tahoe basin are characteristic of Basin and Range faulting and place the Tahoe basin within the western limits of the extensional Basin and Range province.

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