Initial Steps Toward Next-Generation, Waveform-Based, Three-Dimensional Models and Metrics to Improve Nuclear Explosion Monitoring in the Middle East; Conference paper

摘要

In an effort toward improving current seismic-velocity models for the Middle East, the initial Step of building a high-quality database of recordings from well characterized sources is essential. This high-quality database of recordings, or broadband waveforms, encompassing the region from the Mediterranean to the eastern edge of Tibet, will be the primary measure for evaluation and improvement in the iterative, waveform-based, adjoint-inversion process. Adjoint inversions, as with any waveform-based method, require precise estimates of the location, especially depth, and the faulting parameters or moment-tensor elements of the seismic sources. Imprecise locations and/or source terms will result in real changes in the amplitude and the phase of the incoming wave train; when close to a nodal plane, these changes can occur very rapidly with incoming azimuth. These errors will directly map into the resulting velocity model as uncertainty or biased values. The initial database included about 250 well recorded, regional events in the Middle East from 1990 to 2007 with magnitudes Mw> 5.5. To reduce errors in the source-depth and faulting parameters, the events were evaluated using two complementary sets of data, a regional data set contained within the Middle East and a global teleseismic data set. Regional data were first utilized at long period, omega > 20s, using the waveform-based methods of Pasyanos et al. (1996) to determine the moment tensor elements. Then shorter periods, omega > 5 s, were added, following Zhao and Helmberger (1994), to further assess errors in source depth and propagation effects by splitting apart the longer period surface waves from the shorter period, depth-sensitive Pnl waves. Problematic, or high-error, stations and paths were higher analyzed to identify systematic errors with unknown sensor responses and complex wave propagation regions.