Dept. Earth and Ocean Sciences
University of British Columbia
Canada
Email:
bostock@geop.ubc.ca
poster/oral: oral
| The next decade will likely see a substantial increase in the number of broadband, three-component instruments available for targetted studies of lithospheric and mantle structure. To fully realize the potential of this opportunity will require that seismologists effectively exploit multichannel recordings of scattered waves. We are examining this problem in the context of inverse scattering of teleseismic wavefields. In a preliminary study, we have developed a practical yet formal inversion procedure that permits the recovery of 2-D structure from teleseismic recordings made on dense linear arrays. The approach is based on the assumption of high-frequency, single (ie linearized) scattering and incorporates free-surface interactions. Ongoing work is focussed on accounting for non-linear aspects of the problem. We have applied the 2-D inversion approach to investigate crust and mantle structure in the southern Cascadia subduction zone using data recorded during the IRIS-PASSCAL CASC93 experiment. We find very low S-velocities in the cold mantle forearc as evidenced by the exceptional occurrence of an "inverted" continental Moho that reverts to normal polarity seaward of the Cascade arc. This observation provides compelling evidence for a highly hydrated and serpentinized forearc, consistent with thermal and petrologic models of the mantle wedge. The identification of this structure may have important implications for our understanding of the downdip rupture limit of great thrust earthquakes and the genesis of arc magmas. |