Surface Wave Identification Research in the Middle East and North Africa
Abstract
We are in the process of making improvements in surface wave identification throughout the Middle East and North Africa. Seismic surface waves have long played an important role in nuclear explosion monitoring by providing both information about the lithosphere they pass through and the source that generated them. We have made high resolution group velocity maps of the Middle East and North Africa using the tomographic inversion of more than 10,000 individual path measurements. These maps provide valuable constraints on models of the underlying structure of the region. The maps also provide estimates of expected phase of new events that can be used in phase match filters to compress the expected signal and thus improve the signal-to-noise ratio. Of very high interest is improving the performance of the traditional MS:mb discriminant and extending the discriminant down to events with smaller magnitude that are recorded at closer regional distances. This paper directly addresses the improvement that phase match filters bring to the estimation of the surface wave magnitude, MS. We have estimated MS for over 8000 events at 30 stations, both with and without the use of phase match filters, and have found a marked improvement in our ability to discriminate between earthquakes and explosions. When considering smaller magnitude events, however, several other problems emerge. In our analysis, for example, deep events can flag as "explosion-like" using the mb:MS discriminant, since they are also inefficient generators of surface waves. If unidentified as deep events or classified as ?normal? depth events, they can contaminate the actual distribution of surface wave magnitudes (and their derived discriminants) for shallow earthquakes. It is clearly very important to independently identify the source depth of these events in order to avoid misclassifying them. One possible method is through the use of waveform modeling.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2000
- Accession Number
- ADA529911
Entities
People
- Arthur Rodgers
- Michael Pasyanos
- Peter A. Goldstein
- William R. Walter
Organizations
- Lawrence Livermore National Laboratory