Seismic Discrimination of Earthquakes and Explosions, with Application to the Southwestern United States

Abstract

This study examines seismic discrimination between underground nuclear explosions and earthquakes in the Southwestern United States. A thorough review of theoretical and applied research on this problem, especially as it relates to that region, is presented first, followed by a presentation of the seismic discrimination parameters computed for a suite of events in the Southwest and a series of experiments with multi-dimensional discrimination. Review of past work finds some theoretical support for successful discrimination based upon several distinct measurements on seismic recordings. Although negative first motion and presence of pP both indicate a natural earthquake source, they cannot be found confidently in many cases. The relative level of shear-wave and Love-wave phases should be a good classification parameter. The long-period P spectrum of explosions should be diminished due to the surface interaction and consequent cancellation by pP. The region under study extends from California to the southern Rocky Mountains and from roughly 40 degrees N to the Gulf of California. A region of high seismicity, it is also a complex region encompassing several tectonic provinces, including the Basin-Range Province where the Nevada Test Site is located. In general, seismic discriminant parameters obtained from the recordings reflected the theoretical expectations of earthquake-explosion differences. Path-station effects were large for every parameter, especially for short-period data.

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