SURFACE SLIP DURING LARGE OWENS VALLEY EARTHQUAKES

Compilation of geomorphic offsets along-strike enables the assessment of fault-slip distributions for past earthquakes and provides key insight into fault behavior. With the advent of high-resolution lidar topography and imagery, such studies contribute to an increasing inventory of well-described earthquake ruptures useful for characterizing earthquake magnitude and potential. The 1872 Owens Valley earthquake ranks among the largest historical surface ruptures in California, although sparse data and rupture trace complexities confounded earlier attempts to define the slip distribution and reconcile the total moment release. Here, we seek an improved understanding of Owens Valley fault slip to test for slip variability and patterns of moment release. We present a new and comprehensive record of surface slip for 1872 and earlier Owens Valley earthquakes based on combined lidar and field observations. Our lidar investigation utilizes a newly developed analytical tool to measure fault separation based on the cross correlation of linear topographic features. Our results include 180 new point measurements of lateral and vertical separation from landforms mapped in the field, with lateral displacements ranging up to 87 m. Stacking individual probability density functions of fault slip along-strike to form cumulative offset probability distribution plots (COPDs) highlights common values corresponding to single event and cumulative fault displacements. Lateral offsets contributing to the 1872 peak range from ~1.0 to 6.0 m and average ~3.1 m. Vertical separation measured from these offsets ranges from ~0.1 to 2.0 m and is predominantly east-side-down with a mean of ~1.0 m. The corresponding average horizontal-to-vertical ratio of slip is ~5:1 m. Progressively larger COPD peaks attributed to earlier surface ruptures imply a similar amount of slip (~4 m) to the most recent event. Lateral slip during these events ranges from ~3-9 m, 8-14 m, and 13-19 m. COPD peaks evident for past ruptures are relatively complex and bimodal, reflecting heterogeneous slip along geometric fault segments and subordinate fault strands. Evaluating these cumulative displacements in the context of dated landforms in the Owens Valley suggests relatively constant, modest rates of fault slip (~1 mm/yr) over the Mid-to-Late Quaternary.