Collaborative Research: Seismic Imaging of Aseismic Transients

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Airborne Laser Swath Mapping of the Southern San Andreas Fault This project is using Airborne Laser Swath Mapping (ALSM) technology, also known as LIDAR, to perform a very high resolution topographic survey of the San Andreas fault (SAF) and other selected fault segments in southern California. Aerial photography obtained during this survey will be draped over the topographic dataset to produce a highly detailed characterization of the earth's surface in the near field of the fault. The intent is to image the fault system in great detail prior to the next great earthquake, i.e. the 'Big One', so that when this event occurs it will be possible to map the near-field displacement and deformation field with unprecedented accuracy. Post-event resurveys of the fault system will determine slip and afterslip heterogeneity, and so help resolve several long-standing debates in earthquake source physics. It will also be possible to characterize near-field deformation associated with the along-strike transition from continuously-creeping to fully-locked sections of the SAF. The project makes extensive use of the new National Center for Airborne Laser Swath Mapping (NCALM) facility, as well as the UNAVCO Inc. facility (to borrow Global Positioning System (GPS) receivers to support aircraft positioning). The NCALM facility will acquire the survey data using the University of Florida's aircraft, LIDAR and digital camera. The aircraft will operate at low altitude (~600 m) to ensure excellent horizontal resolution and vertical accuracy. It will fly along sets of parallel tracks, roughly centered on the fault, so as to obtain sets of overlapping swaths: this redundancy in ground coverage will enable systematic quality control, and provide a means to avoid shadowing problems in steep terrain. The aircraft will be positioned using a combination of inertial guidance and GPS. Kinematic GPS positioning of the aircraft will make use of numerous GPS base stations established every 30 km along the flight path. The ALSM data will at first be analyzed by NCALM using their standard data processing techniques. The point cloud (X,Y, Z and intensity) observations will be provided to OSU, who will then compare them with ground truth data so as to provide external validation. Once validated the raw data and the initial 'bare earth' digital elevation model (DEM) will be released to the general scientific community via the NCALM data archive in UC Berkeley. Probably, this will take about 6 months. The data will be reanalyzed at a more leisurely pace at OSU to see if additional improvements can be made. The OSU team members are also be responsible for draping the digital photography obtained during the ALSM survey onto the preliminary and final DEMs. Once this registration process is complete, the combined product will be tied to a wide range of existing imagery and topographic datasets, including: 1) ASTER, MODIS and Landsat hyperspectral imagery data available through NASA-USGS cooperative efforts, 2) SRTM topographic data from NASA and JPL, 3) USGS topographic data from the National Elevation Dataset, 3) NOAA Coastal Services Center topographic data acquired in late 2002 by EarthData International using GeoSAR, 4) air photos, e.g., low sun-angle, high resolution sets that were flown for the USGS as well as stock photography flown by photogrammetry companies, 5) detailed maps by USGS showing fault zone geomorphology and offsets (e.g., Brown, 1970; Clark, 1984; Wallace, 1990).