Re-evaluating offset measurements in the maximum slip zone of the 1999 Hector Mine Earthquake surface rupture

Francis J. Sousa, Joann M. Stock, Katherine M. Scharer, Kenneth W. Hudnut, Sinan O. Akciz, Ryan D. Witkosky, & Janet C. Harvey

Under Review November 15, 2015, SCEC Contribution #6121

The M7.1 Hector Mine earthquake produced a complex surface rupture through a military base in southern California in 1999. Although the location restricted access to the area immediately after the earthquake, it also limited anthropogenic alteration of the scarp, making this earthquake a good candidate for field and lidar study of rupture characteristics. We present new observations of the rupture based on field mapping and a new airborne laser scan dataset covering the entire surface rupture. Our field study focused on an eight kilometer-long maximum slip zone and resulted in observations of offset features not previously reported during the limited post-event field response (Treiman et al., 2002). Increasing the density of measurements along a straight, single-stranded segment of rupture allows for estimation of along-strike slip-variability which is in agreement with other previously published estimates. Field and lidar-based observations include a new set of co-located horizontal offset measurements, allowing for direct comparison of measurements from both the new and previously published datasets (Treiman et al., 2002; Chen et al., 2015). This analysis provides new insights into the methodology used for making such measurements, including a caution to future workers to avoid geomorphically complex features and seek out straight, orthogonal features to measure offset. This study demonstrates the utility of 4D lidar surveys for studying modification of offset features along the entire length of a major earthquake surface rupture.

Sousa, F. J., Stock, J. M., Scharer, K. M., Hudnut, K. W., Akciz, S. O., Witkosky, R. D., & Harvey, J. C. (2015). Re-evaluating offset measurements in the maximum slip zone of the 1999 Hector Mine Earthquake surface rupture. Bulletin of the Seismological Society of America, (under review).