Regional Seismic Event Characterization Using a Bayesian Kriging Approach

Abstract : This effort focuses on collecting and analyzing regional seismic data for earthquakes and underground explosions to improve seismic event characterization capabilities with regard to monitoring the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Digital data have now been acquired and processed for 267 regional recordings of 160 underground nuclear (UNE) and chemical (UCE) explosions. The explosion data set includes 99 Nevada Test Site (NTS) UNE's recorded by MNV and KNB; 6 Lop Nor UNE's recorded by NIL, ZAL, ULN, WMQ, BRVK and MAKZ; 22 Semipalatinsk (STS) UNE's recorded by WMQ and BRVK; 6 Novaya Zemlya (NZ) UNE's recorded by ARCES and KEV; and one UNE at the Indian Test Site recorded by NIL. In addition, the set includes 20 Former Soviet Union (FSU) peaceful nuclear explosions (PNE) recorded by BRVK and KEV; and 6 STS UCE's recorded by ZAL and BRVK. (Note: not all of these explosions have recordings by all stations listed.) Over 5300 regional recordings, between 3 and 17 degrees, by existing seismic stations of the International Monitoring System (IMS) are also used in this study. The regional recordings correspond to 4173 presumed earthquakes above mb 3.5 in the Reviewed Event Bulletin (REB) that were processed at the prototype International Data Center (pIDC). Maximum amplitude measurements of Pn, Pg, Sn and Lg have been computed in several frequency bands ranging from 2 Hz up to 14 Hz (depending on the Nyquist frequency of a given station). The data for the presumed earthquakes have been used to estimate attenuation corrections for Pn/Sn and Pn/Lg amplitude ratios in the 2-4, 4-6, 6-8, and 8-10 Hz passbands for tectonic and stable region types. The regional phase amplitude ratios are further corrected for path variations using a Bayesian Kriging algorithm.