Lg-Wave Propagation in Heterogeneous Media
Final rept. 15 Feb 1988-14 Feb 1989
AUSTRALIAN NATIONAL UNIV CANBERRA RESEARCH SCHOOL OF EARTH SCIENCES
Pagination or Media Count:
The Lg wave is of importance for nuclear discrimination problems because it is commonly the largest phase on a seismic record at regional ranges. It is therefore likely to be detected even for quite small events. The energy comprising Lg is dominantly guided in the crustal waveguide which is known to be a region with very considerable horizontal variability in properties. The effect of heterogeneity on Lg and other regional phases has been assessed by the development of a new method for the description of seismic wave propagation processes in laterally varying media. This scheme is based on propagation operators which allow for the major processes of interconversion between seismic wavetypes. This approach is used to generate descriptions of the propagation processes contributing to the main regional seismic phases Pn, Pg, Sn and Lg. These representations are then used to examine the theoretical basis for the discriminants between earthquakes and underground nuclear explosions based on the relative amplitudes of P and S waves. The ratio of Sn to Pn amplitude looks promising as a high frequency discriminant. However, the ratio of Lg to Pn amplitudes is not as useful because of the complex nature of the propagation characteristics of Lg.
- Seismic Detection and Detectors
- Nuclear Weapons