HR: 14:25h
AN: T43C-04    [Abstracts]
TI: Seismic Attenuation Structure of the Mariana Subduction System
AU: * Pozgay, S H
EM: spozgay@wustl.edu
AF: Washington University, Department of Earth Sciences, 1 Brookings Drive, St Louis, MO 63130, United States
AU: Wiens, D A
EM: doug@kermadec.wustl.edu
AF: Washington University, Department of Earth Sciences, 1 Brookings Drive, St Louis, MO 63130, United States
AU: Conder, J A
EM: conder@ seismo.wustl.edu
AF: Washington University, Department of Earth Sciences, 1 Brookings Drive, St Louis, MO 63130, United States
AU: Shiobara, H
EM: shio@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AU: Sugioka, H
EM: hikari@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution (IFREE), JAMSTEC, 2-15 Natsushima Cho, Yokosuka, 237-0061, Japan
AB: Analysis of the anelastic structure of a subduction zone can place first-order constraints on variations in temperature and volatile content. We investigate seismic attenuation across the western Pacific Mariana subduction system using data from the 2003-2004 Mariana Subduction Factory Imaging Experiment. This 11 month experiment consisted of 20 broadband stations deployed on islands and 58 semi-broadband ocean bottom seismographs deployed across the forearc, island arc, and back-arc spreading center. Following Stachnik et al. [2004], we compute the amplitude spectra for P and SH arrivals for a given local earthquake and simultaneously invert for the path-averaged attenuation parameter, t*, for each waveform and the seismic moment and corner frequency for each earthquake. Measurements are taken over a frequency band of 0.05 to ~10 Hz, although poor signal to noise along high-attenuation mantle wedge paths limit observations to < 2-3 Hz in some cases. Tomographic inversion of the ~3000 t* measurements shows low attenuation along raypaths traveling through the subducting Pacific plate. A high attenuation anomaly beneath the island arc extends to ~60-80 km depth and is distinctly separated from the higher attenuation anomaly beneath the backarc spreading center. The westward-trending asymmetric backarc anomaly extends to ~100 km depth. We interpret the arc and trough anomalies as due predominantly to increased temperatures. Further exploitation of attenuation-temperature relationships will elucidate which anomalies are thermally controlled versus which are controlled by other mechanisms, such as the presence of volatiles or partial melt.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7270 Tomography (6982, 8180)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting