Investigation of Upper Mantle Structure in Central Eurasia from Analysis of Broad-Band Far Regional Seismograms (and Comparison to Western U.S.)

摘要

Waveforms from nuclear explosions at the E. Kazakhistan test site were recordedat ARU GAR at the distance range studied for Nevada Test Site explosions (between 1380 and 1540 km). Waveforms at ARU are characterized by weak initial P waves following by strong secondary arrivals within 5 seconds. Within approximately 14 seconds comes a strong later arrival, preceded by a longer-period arrival. Filtering in different frequency bands shows initial P wave long period arrival are consistent with an amplitude ratio of 1:2. Other arrivals are high-frequency vanish for periods longer than 2 sec. Synthetic reflectivity seismogram calculations test previous P wave models for Central Eurasia for compatibility with identified waveform patterns. Most models produce impulsive 1st arrivals fail to generate strong secondary arrivals. Only models by Mechie et al. (1993) Priestley Cipar (1994) show some observed P wave patterns. With a new model strong secondary arrivals are generated with observed frequencies attribute these arrivals to a Moho underside reflection free surface reflection PP. (MM).