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Comparison of long shot and earthquakes Currie, Ralph Gordon

Abstract

The seismic signal generated by the underground nuclear explosion, Long Shot, has been compared with seismic signals of earthquake origin and found to be similar on a regional scale. Negative Long Shot magnitude residuals are associated with areas of recent tectonic activity as are late arrivals, while positive Long Shot magnitude residuals and early arrivals have been found to be associated with tectonically stable regions. These trends are coincident with those indicated by data from other seismic events. The more detailed comparison of Long Shot and earthquake magnitude residuals at Penticton and Port St. James indicates that the Long Shot residuals also reflect the location of the source. At these stations, earthquakes with distances and azimuths comparable to Long Shot exhibit magnitude residuals that are most similar to those of Long Shot. The magnitude residuals at the University of British Columbia exhibit the same dependence on source parameters although a direct comparison with Long Shot could not be made. An examination of earthquake travel time residuals at Penticton and Fort St. James also indicates the same dependence on source location. Long Shot surface waves indicate an average unified magnitude of 5.1 at Canadian stations as compared with an average unified magnitude of 6.0 from body waves at the same stations. The comparison of the power spectra of Long Shot and earthquakes at Leduc and Victoria indicates relatively more energy at high frequencies from Long Shot than from earthquakes. This variation in spectral decrement is interpreted as an effect of the different source mechanisms. The spectrum of Long Shot at Rocky Mt. House appeared to be anomalous as it had a significantly larger spectral decrement than at the other stations and was indistinguishable from the spectra of earthquakes recorded at Rocky Mt. House. The trend of the power spectra also appear to be partially determined by the crustal and upper mantle structure in the vicinity of the station. The effect of the source parameters and travel path is also indicated by a tendency for the spectral decrement to increase with increased distance to source and with increased depth.

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