Differencing of airborne laser scanning data acquired before and after the 2014 South Napa earthquake Abstract

abstract

  • Post-earthquake airborne laser scanning (ALS) data allow rapid and high-resolution analysis of fault ruptures and hazards. Differencing techniques used to quantify surface displacements along the rupture and associated secondary effects including mass movements, liquefaction, and subsidence, also require pre-event reference data. Such data are increasingly likely to be available for surface rupturing earthquakes in the U.S. and Japan, where ALS covers many active deformation zones. We are exploring new ways to observe earthquake effects and ground deformation using laser scanning, which affords scale and resolution that complement other ground- and space-based methods imaging of coseismic deformation. For the Aug. 24, 2014 South Napa earthquake, pre-earthquake ALS data had been acquired over the Napa Watershed by NCALM in 2003 (http://dx.doi.org/10.5069/G9BG2KW9). These data present an opportunity to create surface displacement fields, so DWR, CGS, USGS, PEER and GEER contracted to acquire ALS data on Sept. 9, 2014 (Hudnut et al., AGU EOS 2014, Hudnut et al., USGS OFR 2014-1249, hddsexplorer.usgs.gov, and www.opentopography.org). We used both a standard open-source iterative closest point (ICP) differencing approach and newly refined ICP (with weighting scaled by trajectory and scanning geometry) to analyze the co-seismic displacement field, and independently showed that it reaches a local maxima of ~50 cm. We have checked point cloud density and calibrations, and identified and removed artifacts across the project area. DEMs have been produced by several methods in support of fault hazard mapping by CGS and ground failure checks along levees by DWR. In addition to these latest findings using the two data sets, we compare the performance of our refined and open-source ICP methodologies for determining surface displacements across this region of distributed fault rupture.

publication date

  • 2015