Bg. Bukchin et al., Isotropic and nonisotropic components of earthquakes and nuclear explosions on the Lop Nor test site, China, PUR A GEOPH, 158(8), 2001, pp. 1497-1515
We test the hypothesis that the existence of an observable non-zero isotrop
ic component of seismic moment can be used as a discriminant to distinguish
nuclear explosions from shallow earthquakes. We do this by applying the me
thod described herein to a small set of data recorded between 1990 and 1996
following events (seven nuclear explosions, three earthquakes) that occurr
ed on the Lop Nor test site in Western China. We represent each source as a
sum of an isotropic component at the surface and a nonisotropic, double-co
uple component at an estimated depth. The explosions all possess a signific
ant nonzero isotropic component and the estimated depth of the double-coupl
e component of the moment tensor, presumably the result of tectonic release
, lies between about 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 still
very small, suggests that certain source characteristics (namely, double-c
ouple depth and the ratio of the isotropic to nonisotropic components of se
ismic moment) may prove useful in discriminating explosions from shallow ea
rthquakes, Further work is needed to determine whether these observations h
old for explosions at other test sites, to investigate a much larger set of
shallow earthquakes located in regions of interest, and to study the robus
tness of the estimated source parameters as source magnitude and the number
of observing stations decrease.