Extending Regional Wave Form Modeling to Shorter Periods to Improve the Location and Identification of Small Seismic Sources
Abstract
In an effort to improve the location of small seismic events near known test sites, we are determining source-station specific corrections (SSSC's) for regional P, S and Lg phases recorded at IMS stations within 20 deg of these locals, in particular the central Asian test sites of Lop Nor Semipalantinsk. To this end, we are calculating travel-time residuals between phase arrival information from various sources -- CEB and ISC values as well as direct waveform picks -- and IASP91 predictions using available ground-truth data for events in and near these test sites. These residuals are then averaged for each station to determine the empirical SSSC's. Ground-truth data for these events vary in accuracy; in particular, the level of ground truth for more recent Lop Nor explosions, which are the only ones recorded by many of the newer IMS stations, is not well constrained, being GT25 locations from the Reviewed and Calibration Event Bulletins (REB and CEB). As accurate hypocentral information is crucial to obtaining well-calibrated travel-time corrections, we re-evaluated these more poorly constrained ground-truth data. We found that the ISC locations were quite similar to those of GT5 Lop Nor events which were determined from joint epicenter determinations (JED). For m(b) greater than or equal to 5 explosions the average difference in epicentral locations is 2.9 km, with the maximum being 5.5 km; and differences in origin time being 0.1 sec on average, with the maximum being 0.3 sec. Epicentral errors for these ISC locations are small, being less than 5 km. Discrepancies and errors are significantly larger for the smaller (m(b) less than or equal to 4.7) explosions, and are assumed to be due to SNR phase picking problems and fewer observations used to determine locations. Consequently the ISC teleseismic locations for the m(b) is greater than or equal to 5 explosions can be considered to be of GT5 quality.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2000
- Accession Number
- ADA529902
Entities
People
- Bradley B. Woods
- Chandan K. Saikia
- Hong K. Thio