HR: 1340h
AN: S33A-1039    [Abstracts]
TI: Upper Crustal Velocity Model of the Goldstream Valley, Central Alaska
AU: * Dougherty, S L
EM: doughesb@bc.edu
AF: Boston College, Department of Geology and Geophysics, Devlin Hall 213, 140 Commonwealth Ave., Chestnut Hill, MA 02467, United States
AU: * Dougherty, S L
EM: doughesb@bc.edu
AF: Weston Geophysical Corporation, 181 Bedford St. Suite 1, Lexington, MA 02420, United States
AU: Ebel, J E
EM: ebel@bc.edu
AF: Boston College, Department of Geology and Geophysics, Devlin Hall 213, 140 Commonwealth Ave., Chestnut Hill, MA 02467, United States
AU: Leidig, M
EM: mleidig@westongeophysical.com
AF: Weston Geophysical Corporation, 1004 Augusta Dr., Houston, TX 77057, United States
AB: A series of five explosions were detonated in the schist bedrock of the Goldstream Valley region of central Alaska and recorded on more than 120 local sensors to develop 1-D and 3-D models of the upper crust. Simple refraction analyses reveal that both P- and S-wave arrival times are azimuth dependent, with the fastest velocities seen in the north and northeast for P-waves and in the southeast and northeast for S-waves. In one layer over a half-space P models, average velocities of 3.46 ± 0.41 km\backslashs for layer 1 and 4.79 ± 0.53 km\backslashs for layer 2 are seen. Two layers over a half-space models indicate average P-wave velocities of 3.05 ± 0.19 km\backslashs (layer 1), 3.90 ± 0.18 km\backslashs (layer 2), and 5.12 ± 0.35 km\backslashs (layer 3). Analysis of S-wave travel time data yields an average velocity for only one layer (2 or 3), with a value of 2.77 ± 0.47 km\backslashs. The azimuthal dependence is modeled with velocity anisotropies of ± 1-10% and ± 2-12% for P and S, respectively, at a fast direction of ~40-70°, which is consistent with the northeast trending fault pattern of the region. Poisson's ratio calculations reveal a well constrained average value of 0.283 ± 0.031 at distances ≥ 7 km and a more scattered value of 0.277 ± 0.062 at 2-7 km distance from the source. These values are consistent with known Poisson's ratios for mica-quartz schist and greenschist or amphibolite facies pelitic schist, which are the major geological components of the region. The highly scattered Poisson values at close distances are likely due to the higher porosity of the bedrock at low pressures. In addition to the simple travel time analysis, the S-wave velocity structure of the upper crust is determined through multiple filter analysis and inversion of 0.4-2 sec period Rg waves. The resulting shear wave velocity model is incorporated into the refraction analysis results to help constrain the 1-D and 3-D models of the area.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
SC: Seismology [S]
MN: 2007 Fall Meeting