HR: 1330h
AN: T12D-0497    [PDF]
TI: Crustal Structure of the Northern Juan de Fuca Plate From Marine Seismic Refraction and Gravity Data
AU: * McClymont, A F
EM: amcclymont@eos.ubc.ca
AF: Dept. Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
AU: Clowes, R M
EM: clowes@lithoprobe.ubc.ca
AF: Dept. Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
AB: A seismic refraction experiment was conducted in 1980 as part of the Vancouver Island Seismic Project (VISP80). Profile VISP II was positioned to provide insight into the structure of the oceanic crust on the northernmost part of Juan de Fuca plate. The refraction data were recorded on three ocean bottom seismometers (OBSs) deployed at the ends and middle of a 110 km line oriented parallel to the deformation front of the Cascadia Subduction Zone. An airgun source at 0.5 km spacing and explosive charges at $\sim$ 2.5 km spacings were fired into the OBSs. Direct, converted and reflected phases are observed from vertical and horizontal component geophones. A velocity model is constructed using forward ray trace modeling and synthetic seismograms are produced from this model for comparison with the recorded seismogram sections. Travel time picks for the Pn phase indicate significantly different lower crustal velocity structure toward either end of the profile. The Pn phase picks are modeled by a pronounced increase in igneous crustal thickness of the Juan de Fuca plate, from $\sim$ 7 km at the southern part of the model to $\sim$ 10 km at the northern part. A complementary 2.5-D gravity model is produced. Densities for this model are derived from the velocity model using a general relation between P-wave velocity and density for typical oceanic crust. The gravity anomaly calculated from the model of thick crust is not replicated in the free-air gravity field. The P-wave velocities and densities required to match the gravity data may be explained by serpentinization of the uppermost mantle.
DE: 0930 Oceanic structures
DE: 0935 Seismic methods (3025)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting