Isotropic and Nonisotropic Components of Earthquakes and Nuclear Explosions on the Lop Nor Test Site
COLORADO UNIV AT BOULDER
Pagination or Media Count:
We test the hypothesis that the existence of an observable isotropic component of the seismic moment tensor can be used as a discriminant to distinguish nuclear explosions from shallow earthquakes. We do this by applying the method described by Bukchin et al., 2000 to a set of data recorded between 1990 and 1996 following events seven nuclear explosions and three earthquakes that occurred on the Lop Nor test site in Western China. We represent each source as the sum of an isotropic component at the surface and a nonisotropic, double couple component at an estimated depth. The explosions all possess a significant isotropic component, and the estimated depth of the double-couple component of the moment tensor, presumably the result of tectonic release, lies between 0 and 3 km. For the earthquakes studied, the isotropic component is indistinguishable from zero and the depths of the sources are estimated at 3, 17 and 31 km. The data set we have studied, although very small, suggests that certain source characteristics namely, double couple depth and the ratio of the isotropic to nonisotropic components of the seismic moment tensor may prove useful in discriminating explosions from shallow earthquakes. Further work is needed to determine whether these observations hold for explosions at other test sites, to investigate a much larger set of shallow earthquakes located in regions of interest, and to study the robustness of the estimated source parameters as source magnitude and the number of observing stations decrease.
- Numerical Mathematics
- Seismic Detection and Detectors