Local Distance P/S Amplitude Ratios for Event Discrimination

Session: Explosion Seismology Advances [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The ability to discriminate between earthquakes and other seismic signals, including underground explosions, is crucial for global security and test ban treaty monitoring and important for other seismological endeavors. Historically, discrimination for large explosions, such as nuclear tests, from surrounding seismicity could be achieved on the basis of lower shear generation for explosive sources, particularly at higher frequencies, by using seismic P/S amplitude ratios. This method proved effective at many test sites and emplacement conditions around the world for explosions that could be recorded at regional distances (>200 km). However, very little testing of this discriminant exists for data at local distances (< 200 km), and it is poorly understood if P/S ratios would be useful for smaller explosions that require data recorded at shorter distances.

Previous work has looked at the P/S discriminant at local distances using data in granite from the Source Physics Experiment (SPE), a series of well-recorded chemical explosions in southern Nevada designed to improve our understanding and modeling capabilities of the shear energy generated by explosions. This work found that the discriminant may be highly unreliable at these short distances, appearing to work at some stations, but not others. A number of explanations for this inconsistency are possible and require further investigation. One possibility is that differences in the direction of explosion shear energy generation from very near the source region extend a long way before they are scattered and attenuated out at regional distances causing large variations in the expected explosion S-wave amplitude. Another possibility is that earthquake radiation patterns are poorly accounted for at short distances, contributing to excess scattering in the P/S ratios from the earthquake population. We continue investigations into the far-field shear energy estimation using additional data from chemical explosions with different emplacement conditions in dry alluvium geology from Phase II of the SPE.

Presenting Author: Moira L. Pyle

Authors