Pg/Lg Discrimination in the Western United States
Abstract
Various P/Lg ratios have suggested as viable methods of discriminating explosions from earthquakes. However, the performance of these phase ratios as discriminants has been varied depending on the geographic region, the specific phases, and the frequency passband chosen for analysis. Recently installed networks capable of recording broadband and high-frequency digital data present the opportunity of using high-frequency data with possible improvements in discrimination performance. This study measured Pg/LG ratios over the frequency bands 0.5-1.0 Hz, 1-2 Hz, 2-4 Hz and 4-8 Hz for earthquakes and explosions in the western United States using GDSN data. Earthquake and explosion Pg/Lg ratios overlap almost completely for the 0.5-1.0 Hz band; at higher frequencies the Pg/Lg ratio for explosions increases, providing some separation. Smaller explosions tend to look like earthquakes, perhaps due to their shallow depth. The explosion Pg/Lg ratios generally increase with increasing depth in most of the frequency bands studied, which may be due to an increase in source medium velocity with depth, increasing Pg amplitudes relative to Lg. The dominant factor in Pg/Lg ratios appears to be the propagation path. Earthquakes from Southeastern Cal. systematically lower Pg/Lg ratios than those from Nev. The explosions have similar Pg/Lg ratios to the Nevada earthquakes in all frequency bands except 4-8 Hz. This suggests tha for frequencies up to 4Hz, the source-station path may be more important than the source type in determining the Pg/Lg ratio as a discriminant. This is supported by a comparison of the Pg/Lg ratio of three explosions with their corresponding collapses.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 10, 1990
- Accession Number
- ADA226819
Entities
People
- C. S. Lynnes
- R. Baumstark
- R. K. Cessaro
- W. W. Chan