HR: 1340h
AN: T53A-1125    [Abstracts]
TI: Widespread presence of serpentinite within the Cascadia megathrust suggested by teleseismic receiver function analysis.
AU: * Nikulin, A
EM: anikulin@eden.rutgers.edu
AF: Rutgers University, Geological Sciences Rutgers University Wright-Rieman Labs 610 Taylor Road, Piscataway, NJ 08854, United States
AU: Levin, V
EM: vlevin@rci.rutgers.edu
AF: Rutgers University, Geological Sciences Rutgers University Wright-Rieman Labs 610 Taylor Road, Piscataway, NJ 08854, United States
AU: Park, J
EM: jeffrey.park@yale.edu
AF: Yale University, Geology and Geophysics Department Yale University P.O. Box 208109, New Haven, CT 06520-8109, United States
AB: Receiver function analysis of data from long-running observatories located along the West coast of the US in Oregon and Washington is used to characterize the crustal and upper mantle structure of the Cascadian forearc. Our primary goal is to explore along-strike variation in the structure of the crust and the uppermost mantle. Long periods of data collection (5 and more years) allow us to construct well-populated backazimuth and epicentral distance gathers of receiver functions throughout the region. In the area between the coast and the volcanic arc we are able to identify coherent SV-polarized phases consistent with P-S conversion from the top of the subducting Juan-de-Fuca plate. We note that in all cases these phases display significant directional variation, sometimes even switching polarity. We also note that in all cases there is corresponding SH-polarized energy associated with these phases. P-SH scattering has significant amplitude, but does not exhibit polarity changes in the slab dip direction, which means that seismic anisotropy exerts a strong influence on P-S conversion at the top of the Cascadia slab. Beneath Corvallis, Oregon a strongly anisotropic layer on top of the Juan-de-Fuca plate has been related to the presence of serpentinite within the zone of plate contact. Our new results suggest that this feature is wide-spread in Cascadia, although the specific receiver function signature varies considerably. Presence of serpentinized material between tectonic plates of subduction zones has been proposed as an inhibitor to earthquake rupture. We will compare the area of serpentinized plate contact to other constraints on the depth of the seismogenic zone in Cascadia.
DE: 0935 Seismic methods (3025, 7294)
DE: 1734 Seismology
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting