Publication Date:
2002-01-01
Description:
Seismic data recorded at the broad-band teleseismic GRF array and the short-period regional GERESS array, which is a designated IMS primary station, are analyzed to determine the effectiveness of teleseismic P-wave complexity for the purpose of seismic event screening within the framework of Comprehensive Nuclear-Test-Ban Treaty verification. For the GRF array, seismic waveform data from nearly 200 nuclear explosions have been recorded since its installation in the late 1970's, which were studied along with several thousand earthquakes from the last few years. Additionally, we investigated teleseismic P wave complexity for a similar number of earthquakes recorded at GERESS. However, owing to its operation starting in 1991, only a limited number of nuclear explosion seismograms are available for study. For nuclear explosions, complexity does not exceed levels of 0.3 except for a number of events from the Nevada Test Site recorded only at the GRF array and located at a large distance where PcP may interfere with the initial P wavelet. Since all events with complexity at GRF larger than 0.3 are exclusively located on Pahute Mesa within the Nevada Test Site, near-source geology or topography must play a dominant role for these increased complexity values, while PcP may not contribute significantly to the high-frequency energy measured by the complexity parameter. Although many earthquakes show complexities below this level, for more than 25% of the earthquakes investigated the complexities determined are larger than 0.7, thus showing distinctly larger values than nuclear explosions. Therefore, this percentage may be screened as earthquakes from all seismic events detected. As currently only about half of the events detected by the global IMS network are screened out based on focal depth and the mb:Ms criterion, teleseismic P-wave complexity may contribute significantly to the task of seismic event screening.
Print ISSN:
1383-4649
Electronic ISSN:
1573-157X
Topics:
Geosciences
,
Physics
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