Introduction

The need to monitor broader areas and an increasing number of nations with nascent nuclear weapons programs has lead to major challenges to nuclear explosion monitoring research. Agencies must, in fact, be prepared to detect, identify and locate nuclear explosions in wide regions, often aseismic and lacking previous seismic observations from specific test sites. Since the 1980's, the importance of monitoring at regional distances has been well established. However, such monitoring is complicated by the passage of seismic waves through the structurally complex crust and uppermost mantle. As a consequence, traveltimes and amplitudes of regional phases show great variability leading to large uncertainties in event locations and decreased performance of regional discriminants. A major requirement for the accurate modeling of regional seismic data and therefore improved event locations and regional discriminant performance are 3D regional velocity models characterized by high resolution from the crust down to the transition zone.

Our aim is a 3D velocity model of the crust and upper mantle for the geographic region extending from the western Mediterranean to Pakistan, including the aseismic region of North Africa. The joint inversion of different types of seismic data with diverse sensitivity to the crust and mantle is essential to achieve a high resolution image of the structure in this tectonically complex area, where six major tectonic plates and several microplates interact with each other. We expect predictions for seismogram characteristics (phase arrival times, amplitudes, dispersion) based on this new model to match most observations and be useful for event discrimination. Simultaneously, the new model will refine our understanding of the structure and tectonics in the study region.

Berkeley Seismological Laboratory
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