Microquake Activity Associated with Underground Nuclear Testing at the Nevada Test Site

摘要

In the fall of 1976, the Los Alamos Close-In Seismic Network was added to the existing strong motion net deployed around each nuclear test conducted by Los Alamos. Six to ten stations, including both accelerometers and seismometers, are installed within a two-DOB (depth of burial) circle around SGZ (surface ground zero) and operated until the major portion of the microquake activity ceases, usually within 48 hours. Epicentral locations are determined and local magnitudes are calculated from event durations. Four primary conclusions have been reached on the basis of the data analyzed to date: (1) major faults bounding the immediate site of a nuclear test confine the observed microquake activity to the structural block in which the test is conducted; (2) microquake epicenters are generally distributed around the cavity created by the nuclear test with the peak occurrence generally occurring about three cavity radii away from the working point; (3) magnitudes of locatable microquakes apparently distribute randomly over the entire region of activity; and (4) the microquake activity as a function of time appears to be controlled by the collapse phenomenology. (ERA citation 09:001155)