HR: 0800h
AN: S11A-0999    [Abstracts]
TI: Imaging the M7.9 Denali Fault Earthquake 2002 rupture at the Delta River using LiDAR, RADAR, and SASW Surface Wave Geophysics
AU: * Kayen, R
EM: rkayen@usgs.gov
AF: U.S. Geological Survey, MS999, 345 Middlefield Road , Menlo Park, CA 94025 United States
AU: Barnhardt, W
EM: wbarnhardt@usgs.gov
AF: U. S. Geological Survey, Quissett Campus 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Carkin, B
EM: bcarkin@usgs.gov
AF: U.S. Geological Survey, MS999, 345 Middlefield Road , Menlo Park, CA 94025 United States
AU: Collins, B D
EM: bcollins@ce.berkeley.edu
AF: University of California at Berkeley, Dept. of Civil and Enviro. Engineering, Davis Hall, Berkeley, CA 94720` United States
AU: Grossman, E E
EM: egrossman@usgs.gov
AF: U.S. Geological Survey, MS999, 345 Middlefield Road , Menlo Park, CA 94025 United States
AU: Minasian, D
EM: dminasian@usgs.gov
AF: U.S. Geological Survey, MS999, 345 Middlefield Road , Menlo Park, CA 94025 United States
AU: Thompson, E
EM: erict@email.unc.edu
AF: U.S. Geological Survey, MS999, 345 Middlefield Road , Menlo Park, CA 94025 United States
AB: The Mw 7.9 Denali fault earthquake of 3 November 2002 resulted in approximately 5.5 meters of right-lateral offset and sub-meter (0.6m average) up-to-the north vertical displacement of alluvial deposits of the Delta River. We characterize the surface rupture and shallow fault structure of the Denali fault zone at the Delta River in order to better understand these most recent displacements and to estimate the total vertical offset of alluvium above glacially scoured bedrock. To analyze deformations along the fault-trace, we performed tripod-mounted ground-based LiDAR surveys, and Spectral analysis of Surface Wave (SASW) and Ground Penetrating RADAR (GPR) geophysical investigations. These studies were performed between the Trans-Alaska Pipeline (TAPS) corridor on the terrace deposits of the eastern flanks of the Delta River valley and the steeply sloping bedrock surface on the western side of the river. To produce digital terrain models (DTM) of the surface break we used a Riegl Z210i Laser-scanner to image eight independent LiDAR scans, and ISite3D modeling software to merge these scans into three DTM surfaces. We find that using a rotating scanning-laser allows us to produce ultra-high resolution quantitative DTMs for geomorphic analysis that can be used to resolve features and detect topographic changes on a fine-scale (0.9-2.5cm). Local geo-referencing control points are established using fixed auto reflectors. The near subsurface alluvium was imaged using reflection-based (GPR). A suite of parallel and orthogonal GPR reflection lines were measured to develop block models of the surface rupture at two locations. Radar imagery clearly delineates a plane of chaotic reflectors across the rupture zone. To characterize the depth of alluvium over bedrock on either side of the fault, we used the spectral analysis of surface waves (SASW) approach to invert the near-surface shear wave velocity profile. An Alyeska Co. Catepillar D9N track-mounted dozer was used as a high-energy random-wave source for the SASW test. This source allowed us to profile to depths in excess of 200 meters on either side of the fault. We found the combination of LiDAR and GPR allows us to analyze the surface and near-surface characteristics of a complex oblique rupture across the braid bars of the Delta River. SASW-based shear wave velocity profiles on either side of the fault indicate total up-to-the north uplift on the Denali fault of between 60-90 meters since Pleistocene (?) deglaciation. This investigation is the product of a collaborative research and development agreement between the Alyeska Pipeline Services Company, Pacific Gas and Electric Company and the U.S. Geological Survey.
UR: http://walrus.wr.usgs.gov/geotech/
DE: 7223 Seismic hazard assessment and prediction
DE: 0933 Remote sensing
DE: 0935 Seismic methods (3025)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting