HR: 16:30h
AN: NS24A-03    [Abstracts]
TI: Seismic Imaging and Gravity Studies of the Eagle Rock and Raymond Faults in Arroyo Seco, Los Angeles County, California
AU: * Rymer, M J
EM: mrymer@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Fuis, G S
EM: fuis@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Catchings, R D
EM: catching@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Goldman, M R
EM: goldman@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Scheirer, D S
EM: dscheirer@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AB: In August 2007, we acquired high-resolution reflection and refraction data, using both P waves and S waves, across the Eagle Rock and Raymond faults in the Arroyo Seco, Pasadena and South Pasadena, respectively. The studies were conducted to determine the precise location of the faults, their dips, and their possible structural connections. The seismic profiles crossed geologically mapped projections of the faults near the center of the respective profiles. The northern profile, across the Eagle Rock fault, was 1200 m long and was recorded by 240 geophones at 5-m intervals. Seismic sources for the northern line were generated by Betsy-Seisgun ‘shots' at all recording locations and S-wave sources at 70 recording locations distributed symmetrically about the Eagle Rock fault. The southern line, across the Raymond fault, was 450 m long and recorded by 90 geophones at 5-m intervals. Seismic sources for the southern line were generated by combined accelerated weight drops and/or sledgehammer impacts at all recording locations, seisgun shots at a few locations, and S-wave sources at 70 locations. Preliminary shot gathers of P-wave data for both northern and southern profiles demonstrate abundant, robust reflectors. We used a tomographic velocity image from the P-wave data in order to image the structure of faults in both profiles. The resulting velocity models will be used to help migrate the acquired seismic reflection data. We will also create tomographic velocity images from the S-wave data in order to calculate Poisson's ratio and Vp/Vs ratio along the profiles. In addition, gravity data were acquired along both northern and southern profiles at 25-m intervals. Preliminary processing of the gravity data indicates lateral variations in rock density that we will combine with seismic results in the final interpretation.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7250 Transform faults
DE: 8107 Continental neotectonics (8002)
DE: 8175 Tectonics and landscape evolution
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting