Source and Path Calibration in Regions of Poor Crustal Propagation Using Temporary, Large-Aperture, High-Resolution Seismic Arrays

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Conference Proceeding

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Broadband seismic data acquired during the Hi - CLIMB field experiment are used to study seismic events and path propagation in the Nepal Himalaya and south - central Tibet an Plateau . S imilarities in regional prop agation between Tibet and Iran motivate this new study . The 2002 – 2005 Hi - CLIMB experiment consisted of 233 stations distributed along a dense 800 km linear north - south array extending from the Himalayan foreland into the central Tibeta n Plateau. The main array was flanked by a 350 km x 350 km sub - array in southern Tibet and central and eastern Nepal. Our dataset provides an opportunity to obt ain seismic event locations for ground truth (GT) evaluation, with emphasis on depth, to determine source parameters, and to study distance evolution of seismic coda for yield estimation in low Q regions. Event detection and preliminary automatic loca tion analysis show tens of thousands, otherwise undetected, local seismic events. We will obtain high - quality event locations from manual P- and S- wave picks by joint inversion for location and 2D and 3D velocity structure . We will also perform relative locations to resolve spatial relations of several highly active event clusters. Besides GT - compatibility, high - quality locations are essential for the source parameter and coda evolution portions of the study. We will perform moment tensor inversions in a wi de magnitude range (1.5 ≤ Mw ≤ 6) , paying particular attention to event depth and size. Full waveform m oment - tensor depth is important for validating traveltime - derived depth ; seismic moment calibrates spectral coda levels and local and regional magnitudes. The dense station spacing of the Hi - CLIMB array is unique for any highly attenuating crustal path region , permitting fine - scale analysis of decay properties for multiple coda types, which is a globally important, unresolved issue in monitoring research. The GT - level locations and moment tensor depths will contribute to Seismic Location Baseline Model (SLBM) tomographic efforts, allow evaluation of depth mislocation for crustal models, and enhance model accuracy throughout central and southern Asia.

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Proceedings of the 2009 Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies, v. 1, p. 158-165