MAGNITUDE DETERMINATION AT REGIONAL AND NEAR-REGIONAL DISTANCES IN THE UNITED STATES
Abstract
This report deals with the problems of variation of P sub n amplitudes in the regional and near-regional distance ranges (200-2100 kilometers). The data used were recorded by Long Range Seismic Measurement (LRSM) vans of the VELA Seismological Center as a result of earthquakes throughout the United States and numerous nuclear and chemical explosions in the same region. It is shown that the patterns of P sub n amplitudes versus delta in Western and Eastern United States (WUS and EUS) are markedly different and that these differences are related to different velocity structures in the two regions. These differences extend to at least 150 kilometers depth. Neither the WUS nor EUS patterns conform even approximately to that predicted or suggested by Gutenberg and Richter in the 1000-2000 kilometer range. The hypothesized shadow-zone does not exist and over-estimation of magnitude by as much as 1.5 magnitude units is frequently done because of failure to properly understand the patterns of radiation. By proper calibration of WUS by use of numerous events, it is now possible to get consistent estimates of magnitude at all distance ranges for most explosions and earthquakes. This is very important when body wave magnitudes are used as an essential element in an identification criterion.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 30, 1965
- Accession Number
- AD0634137
Entities
People
- Jack F. Evernden