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High-resolution seismic compressed high intensity Radar pulse (CHIRP) data and piston cores acquired in Fallen Leaf Lake (FLL) and Lake Tahoe provide new paleoseismic constraints on the West Tahoe-Dollar Point fault (WTDPF), the westernmost normal fault in the Lake Tahoe Basin, California. Paleoearthquake records along three sections of the WTDPF are investigated to determine the magnitude and recency of coseismic slip. CHIRP profiles image vertically offset and folded strata along the southern and central sections that record deformation associated with the most recent event (MRE) on the WTDPE Three faults are imaged beneath FLL, and the maximum vertical offset observed across the primary trace of the WTDPF is ~3.7 m. Coregistered piston cores in FLL recovered sediment and organic material above and below the MRE horizon. Radiocarbon dating of organic material constrained the age of the MRE to be between 3.6 and 4.9 k.y.B.P., with a preferred age of 4.1-4.5 k.y.B.P. In Lake Tahoe near Rubicon Point, approximately 2.0 m of vertical offset is observed across the WTDPF. Based on nearby core data, the timing of this offset occurred between ~3-10 k.y.B.P., which is consistent with the MRE age in FLL. Offset of Tioga-aged glacial deposits provides a long-term record of vertical deformation on the WTDPF since ~13-14 k.y.B.P., yielding a slip rate of 0.4-0.8 mm/yr. In summary, the slip rate and earthquake potential along the WTDPF is comparable to the nearby Genoa fault, making it the most active and potentially hazardous fault in the Lake Tahoe Basin. [ABSTRACT FROM AUTHOR]

The West Tahoe-Dollar Point fault (WTDPF) extends along the western margin of the Lake Tahoe Basin (northern Sierra Nevada, western United States) and is characterized as its most hazardous fault. Fallen Leaf Lake, Cascade Lake, and Emerald Bay are three subbasins of the Lake Tahoe Basin, located south of Lake Tahoe, and provide an opportunity to image primary earthquake deformation along the WTDPF and associated landslide deposits. Here we present results from high-resolution seismic Chirp (compressed high intensity radar pulse) surveys in Fallen Leaf Lake and Cascade Lake, multibeam bathymetry coverage of Fallen Leaf Lake, onshore Lidar (light detection and ranging) data for the southern Lake Tahoe Basin, and radiocarbon dates from piston cores in Fallen Leaf Lake and Emerald Bay. Slide deposits imaged beneath Fallen Leaf Lake appear to be synchronous with slides in Lake Tahoe, Emerald Bay, and Cascade Lake. The temporal correlation of slides between multiple basins suggests triggering by earthquakes on the WTDPF system. If this correlation is correct, we postulate a recurrence interval of ~3-4 k.y. for large earthquakes on the Fallen Leaf Lake segment of the WTDPF, and the time since the most recent event (~4.5 k.y. ago) exceeds this recurrence time. In addition, Chirp data beneath Cascade Lake image strands of the WTDPF offsetting the lake fl oor as much as ~7.5 m. The Cascade Lake data combined with onshore Lidar allow us to map the WTDPF continuously between Fallen Leaf Lake and Cascade Lake. This improved mapping of the WTDPF reveals the fault geometry and architecture south of Lake Tahoe and improves the geohazard assessment of the region. [ABSTRACT FROM AUTHOR]