Adjoint Tomography for the Middle East

Adjoint Tomography for the Middle East Shear-velocity event kernel for an earthquake in the strait of Hormuz recorded 2005 by several regional stations. Sensitivities are shown on a horizontal cross-section at 5 km depth and a vertical cross-section through the source and a station location down to a depth of 670 km.
We evaluate 3D models of the Middle East by computing full waveforms for a set of regional earthquakes [Savage et al., 2009]. We measure traveltime shifts between observed broadband data obtained from IRIS and synthetic seismograms for distinct seismic phases within selected time windows using a recently developed, automated measurement algorithm [Maggi et al., 2009]. Based on the measurements for our study region, we selected a best model to feature as the starting seismic model for a fully numerical 3D seismic tomography approach.
</p><p>In order to improve the initial 3D seismic model, the sensitivity to seismic structure of the traveltime measurements for all available, regional network recordings is computed. As this represents a computationally very intensive task, we take advantage of an adjoint method combined with spectral-element simulations [Tromp et al., 2005]. We calculate such sensitivity kernels for all seismic events and regional records and use them in a conjugate-gradient approach to iteratively update the 3D seismic model. This will lead to various improvements of the initial seismic structure in order to better explain regional seismic wave-forms in the Middle East for nuclear monitoring.
</p><p>Maggi, A., C. Tape, M. Chen, D. Chao and J. Tromp, 2009. An Automated time-window selection algorithm for seismic tomography, Geophys. J. Int., 178, 257–281.
</p><p>Savage, B., D. Peter, B. Covellone, A. Rodgers and J. Tromp, 2009. Progress towards next generation, waveform based three-dimensional models and metrics to improve nuclear explosion monitoring in the Middle East, Proceedings of the 31th Monitoring Research Review of Ground-Based Nuclear Explosion Monitoring Technologies, LLNL-PROC-414451, 9 pages.
</p><p>Tromp, J., C. Tape and Q. Y. Liu, 2005. Seismic tomography, adjoint methods, time reversal and banana-doughnut kernels, Geophys. J. Int., 160, 195–216.
</p><p>Acknowledgements: This research is sponsored by Air Force Research Laboratory and by National Nuclear Security Administration, Contract No. FA8718-08-C-0009.</p>


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