Accession Number : ADA332346

Title :   The Portability of Regional Seismic Discriminants Using Wavetrain Energy Ratios, and mb:Mo to Various Tectonic Regions

Descriptive Note : Final rept.

Corporate Author : WOODWARD-CLYDE FEDERAL SERVICES PASADENA CA

Personal Author(s) : Woods, B. B. ; Saikia, C. K.

PDF Url : ADA332346

Report Date : 07 NOV 1997

Pagination or Media Count : 129

Abstract : We have examined broadband regional waveforms of recent (1988+) NTS underground explosions and earthquakes throughout the Southwestern U.S. and Baja, Mexico recorded by TERRAscope and other IRIS stations in order to characterize seismic sources for the purposes of event identification. We have developed several seismic discriminants based on our observations. The most promising discriminant is the ratio of short-period, vertical component, regional P-wave energy to long-period, three component, surface-wave energy (SP:LP). For this ratio explosions tend to have a higher value than do earthquakes. This discriminant works on the same premise as the difference between the teleseismic body-wave and surface-wave magnitude measurements for which earthquakes are richer in long-period surface-wave energy relative to explosions with the same body-wave magnitude. Another potential discriminant examined is the ratio of P-wave to S-wave energy in the short-period, vertical-component of regional seismograms (SP-P:S). We find that this criterion only yields marginal separation of the source populations but becomes more effective at higher frequency bands or when comparing observations from a single station. However, network-averaged values improve the performance as well. Using regional stations for sources 200 to 1300 km away, the magnitude threshold for the SP:LP discriminant is roughly magnitude 4.0, the limiting factor being the signal level of the Airy phase, while that for the SP-P:S discriminant is roughly magnitude 3.0 for the same distance ranges. We investigate the portability of regional seismic discriminants, which were developed using this southwestern U.S. earthquake and NTS explosion data, by applying them to data from other geographic regions.

Descriptors :   *SEISMIC DATA, *SEISMIC DISCRIMINATION, DATA BASES, NUCLEAR EXPLOSIONS, SURFACE WAVES, WAVEFORMS, UNDERGROUND EXPLOSIONS, EARTHQUAKES, PRIMARY WAVES(SEISMIC WAVES).

Subject Categories : Seismology

Distribution Statement : APPROVED FOR PUBLIC RELEASE