HR: 08:45h
AN: S11D-02    [Abstracts]
TI: High Resolution 3-D Travel-Time Tomography Using Controlled Sources and Earthquakes: Application to the Cascadia Subduction Zone
AU: * Crosson, R S
EM: crosson@u.washington.edu
AF: University of Washington, Earth and Space Sciences Box 351310, Seattle, WA 98195 United States
AB: High quality portable and permanent networks in regions where both earthquake and controlled source observations are made offer perhaps the best opportunity for high-resolution tomographic imaging of earth structure at lithosphere scales. This opportunity exists in the seismically active regions of the Cascadia subduction zone as a result of over 30 years of regional network operation, and controlled source experiments over the past 10-15 years such as the "SHIPS" experiment. Aspects of current methodology for non-linear P wave travel-time tomography will be described, including the use of a single fine grid spacing (in the 1-2 km range at regional scale) for both travel-time and inversion computations, a feedback method that regularizes both the final model as well as iterative changes in the model, and problems associated with the use of current 3-D finite-difference (FD) algorithms for travel-time computation in complex structure. Although the methodology may be reaching the limits of current FD travel-time accuracy for complex structure, extraordinary detail is revealed in parts of the model that are well constrained by observational data. Earthquake relocation with 3-D models has not made major changes in our view of seismicity obtained previously with 1-D models; however, there is now a clearer association between crustal earthquakes and the tectonically "strong" structural units of the forearc crust. At the highest structural resolution, clear details of the complex basin and fault structure of the forearc of Washington are apparent. At a slightly lower resolution regional scale (280x303x85 km grid at 1.45 km grid spacing), structure including the subducted Juan de Fuca slab to depths of approximately 70 km is imaged beneath Puget Sound, showing evidence of complex interaction between the forearc crust, the mantle wedge region, and the subducted slab. In this same region, no evidence of a continental Moho exists, consistent with the idea of a serpentinized mantle wedge in this part of the forearc.
DE: 7218 Lithosphere and upper mantle
DE: 7260 Theory and modeling
DE: 7203 Body wave propagation
SC: Seismology [S]
MN: 2004 AGU Fall Meeting