Using Passive Seismic Methods to Detect Underground Cavities

Abstract:

An underground cavity (or low velocity anomaly) may interact with a seismic wavefield in several ways: scattering or reflecting seismic body waves, changing the dispersion of surface waves, inducing resonances within the cavity, or by generating waves traveling around the cavity interface. In theory, these features may be observed using either active or passive seismic surveys. We explore the possibility of detecting the sites of underground nuclear explosions using passive seismic data first by generating a set of synthetic models and second by a field experiment. We generated 3D synthetics on an idealized representation of the cavity and chimney and estimated constraints on detection. Eight broadband seismometers were deployed around the site of a known underground nuclear explosion (UNE) at the U.S. Nevada National Security Site. Examination of the observed data does not show clear indications of resonance within the cavity and chimney caused by seismic waves from teleseismic, regional, or local earthquakes. Green’s functions of raypaths between station pairs have been generated using seismic interferometry based on ambient seismic noise and these will be used to generate a tomographic model. Prepared by LLNL under Contract DE-AC52-07NA27344. Release number LLNL-ABS-675177.