SCEC Award Number 12188 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Evolution of the Hector Mine Earthquake Surface Rupture: a decadal view
Investigator(s)
Name Organization
Joann Stock California Institute of Technology Sinan Akciz University of California, Irvine
Other Participants Ken Hudnut (USGS) as no-cost collaborator; graduate student Frank Sousa (Caltech)
SCEC Priorities 4b, 4c SCEC Groups Geology, Seismology, FARM
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 We obtained new constraints on the rupture zone of the Mw 7.1 Hector Mine earthquake, Mojave Desert, California, using two sets of LiDAR data (collected in 2000 and 2012), post-earthquake aerial photography, and new field work. This earthquake produced a 48 km long surface rupture with up to 5.2 m of right lateral slip, as measured by field geological investigations shortly after the earthquake (Treiman et al, 2002). With the 2012 LiDAR data we made a ~0.35 m DEM over a ~1 km wide swath along the entire length of the rupture (Sousa et al., 2012a) and used it to identify and measure offset geomorphic features. Subtraction of congruent 0.5 m DEMS made from the 2000 and 2012 point cloud data yields a new raster showing specific and quantifiable areas of erosion and aggradation. Dozens of offset features are still preserved along the bedrock part of the rupture and can be accurately measured in the field. A new maximum offset of 6.7 m +/- 0.5 m right-lateral slip was found a few kilometers south of what was documented as the maximum slip area by Treiman et al (2002). Large-magnitude slip variability (over 1m difference) within short distances (less than 0.5 km) is clearly identifiable within certain parts of the maximum slip zone. Our results address processes of long term evolution of fault scarps as well as coseismic slip variability.
Intellectual Merit We have documented new information about the distribution of slip on a 13 year old strike-slip fault rupture, including the recognition of larger offsets than those previously reported. We have confirmed that there is substantial variability in the amount of strike-slip offset over short distances (< 500 meters), along a straight segment of the fault zone with no subsidiary faults. This has important implications for the dynamics of earthquake rupture. We have developed methods for examining differences in post-earthquake LiDAR point clouds, to quantify the geomorphic changes that occur along fault scarps, which will be useful to compare with theoretical models of fault scarp degradation.
Broader Impacts The project involved two graduate students (Frank Sousa and Janet Harvey). Sousa was trained in LiDAR data processing. Both students were trained in making field observations of recent fault ruptures. The project has strengthened the partnership among the 3 institutions (Caltech, USGS and UC Irvine) and has generated a good working relationship between our group of researchers and the US Marine Corps personnel at 29 Palms Air Ground Combat Center.
Exemplary Figure Figure 2. NAIP 2012 imagery (left) and congruently subtracted raster between 2000 and 2012 LiDAR scans (right) along a segment of the HM surface rupture on Lavic Lake. NAIP imagery shows a basalt outcrop exposed above the dry lake bed. Red line on both images shows field collected GeoXH high precision (~10 cm after post-processing) GPS trace of fault scarp. Difference raster (right) is corrected for a 20 cm static vertical shift between the two LiDAR datasets. At right, beige areas represent zero vertical change from 2000 to 2012. Green areas scale to 15 cm (darkest green) decrease in elevation, purple areas scale to 15 cm (darkest purple) increase in elevation over same time span. Sharp scarp is clearly delineated on the LiDAR difference raster. Figure created by Frank Sousa.
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