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Observation of pulses on an interface

TEXAS INSTRUMENTS INCORPORATED, DALLAS 35, TEXAS

Abstract

Recent theoretical results show that, in addition to P and S pulses, two pulse-like phenomena, denoted by and , can be defined near the boundary of an elastic solid. The pulse is the classic Rayleigh pulse in Lamb's problem and is the classic Stoneley pulse in Cagniard's problem. When the Stoneley existence conditions are violated, the pulse still exists for many solid pairs and can be regarded as a radiating interface pulse. The pulse is distinct only when (Poisson's ratio) is greater than about 0.4. It seems to be the dual to the pulse. It is the classic Stoneley pulse in Strick's problem. The pulse has been observed by Kisslinger in loess and clay near Florrisant, Missouri. The radiating pulse has been observed by Pod''yapol'ski and Vassil'ev on a clay/granite interface, and by Roever and Vining on a fluid/solid interface. Roever and Vining may also have observed the pulse on pitch. Two dimensional seismic model studies of the pulse suggest that it is most easily recognized from its particle orbit. Model results for both the trapped and the radiating pulse agree well with theoretical calculations of orbital motion and orbital tilt. The tilt of the orbit in Lamb's problem is virtually independent of the elastic parameters and the velocity is very nearly twice the S velocity. In dispersion problems both radiating and pulses appear as kinks in the dispersion curves.

Footnotes

Freeman Gilbert is now at the University of California, San Diego, California.

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