Surface Slip During Large Owens Valley Fault Earthquakes

The 1872 Owens Valley earthquake is the third largest known historical earthquake in California. Relatively sparse field data and a complex rupture trace, however, inhibited attempts to fully resolve the slip distribution and reconcile the total moment release. We present a new, comprehensive record of surface slip based on lidar and field investigation, documenting 162 new measurements of laterally and vertically displaced landforms for 1872 and prehistoric Owens Valley earthquakes. Our lidar analysis uses a newly developed analytical tool to measure fault slip based on cross‐correlation of sublinear topographic features and to produce a uniquely shaped probability density function (PDF) for each measurement. Stacking PDFs along strike to form cumulative offset probability distribution plots (COPDs) highlights common values corresponding to single and multiple‐event displacements. Lateral offsets for 1872 vary systematically from ∼1.0 to 6.0 m and average 3.3 ± 1.1 m (2σ). Vertical offsets are predominantly east‐down between ∼0.1 and 2.4 m, with a mean of 0.8 ± 0.5 m. The average lateral‐to‐vertical ratio compiled at specific sites is ∼6:1. Summing displacements across subparallel, overlapping rupture traces implies a maximum of 7–11 m and net average of 4.4 ± 1.5 m, corresponding to a geologic Mw ∼7.5 for the 1872 event. We attribute progressively higher‐offset lateral COPD peaks at 7.1 ± 2.0 m, 12.8 ± 1.5 m, and 16.6 ± 1.4 m to three earlier large surface ruptures. Evaluating cumulative displacements in context with previously dated landforms in Owens Valley suggests relatively modest rates of fault slip, averaging between ∼0.6 and 1.6 mm/yr (1σ) over the late Quaternary

A 50,000-year record of lake-level variations and overflow from Owens Lake, eastern California, USA

A continuous lake-level curve was constructed for Owens Lake, eastern California by integrating lake-core data and shoreline geomorphology with new wind-wave and sediment entrainment modeling of lake-core sedimentology. This effort enabled refinement of the overflow history and development of a better understanding of the effects of regional and global climate variability on lake levels of the paleo-Owens River system during the last 50,000 years. The elevations of stratigraphic sites, plus lake bottom and spillway positions were corrected for vertical tectonic deformation using a differential fault-block model to estimate the absolute hydrologic change of the watershed-lake system. New results include 14C dating of mollusk shells in shoreline deposits, plus post-IR-IRSL dating of a suite of five beach ridges and OSL dating of spillway alluvial and deltaic deposits in deep boreholes. Geotechnical data show the overflow area is an entrenched channel that had erodible sills composed of unconsolidated fluvial-deltaic and alluvial sediment at elevations of ∼1113–1165 m above mean sea level. Owens Lake spilled most of the time at or near minimum sill levels, controlled by a bedrock sill at ∼1113 m. Nine major transgressions at ∼40.0, 38.7, 23.3, 19.3, 15.6, 13.8, 12.8, 11.6, and 10.6 ka reached levels ∼10–45 m above the bedrock sill. Several major regressions at or below the bedrock sill from 36.9 to 28.5 ka, and at ∼17.8, 12.9, and 10.4–8.8 ka indicate little to no overflow during these times. The latest period of overflow occurred ∼10–20 m above the bedrock sill from ∼8.4 to 6.4 ka that was followed by closed basin conditions after ∼6.4 ka. Previous lake core age-depth models were revised by accounting for sediment compaction and using no reservoir correction for open basin conditions, thereby reducing discrepancies between Owens Lake shoreline and lake-core proxy records. The integrated analysis provides a continuous 50 ka lake-level record of hydroclimate variability along the south-central Sierra Nevada that is consistent with other shoreline and speleothem records in the southwestern U.S

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Cambrian and Ordovician rocks in the foreground. i

Chronology of tectonic, geomorphic, and volcanic interactions and the tempo of fault slip near Little Lake, California

New geochronologic and geomorphic constraints on the Little Lake fault in the Eastern California shear zone reveal steady, modest rates of dextral slip during and since the midto- late Pleistocene. We focus on a suite of offset fl uvial landforms in the Pleistocene Owens River channel that formed in response to peri odic interaction with nearby basalt fl ows, thereby recording displacement over multiple time intervals. Overlap between 40Ar/39Ar ages for the youngest intracanyon basalt fl ow and 10Be surface exposure dating of downstream terrace surfaces suggests widespread channel incision during a prominent outburst fl ood through the Little Lake channel at ca. 64 ka. Older basalt fl ows fl anking the upper and lower canyon margins indicate localization of the Owens River in its current position between 212 ± 14 and 197 ± 11 ka. Coupled with terrestrial light detection and ranging (lidar) and digital topographic measurements of dextral offset, the revised Little Lake chronology indicates average dextral slip rates of at least ~0.6–0.7 mm/yr and <1.3 mm/yr over intervals ranging from ~104 to 105 yr. Despite previous geodetic observations of relatively rapid interseismic strain along the Little Lake fault, we fi nd no evidence for sustained temporal fl uctuations in slip rates over multiple earthquake cycles. Instead, our results indicate that accelerated fault loading may be transient over much shorter periods (~101 yr) and perhaps indicative of time-dependent seismic hazard associated with Eastern California shear zone faults