Infrasound studies and seismic station development

A large-scale set of experiments involving measurement of infrasound (long period acoustic signals) from high altitude explosions on rockets launched at White Sands Missile Range (WSMR) was conducted during 2005 and 2006. Studies of the infrasound signals from the explosions determined that propagation patterns were predictable from climatology data but that the predictions of explosive yield using established period/yield relationships underestimated known yields by about one order of magnitude. In addition, yield estimates did not scale at source heights greater than about 40 km indicating some physical change in the atmosphere above these heights that was not included in the scaling relations.; A subsequent study to the WSMR experiments motivated by the apparent discrepancies in yield estimation and studies of infrasound propagation to distances less than about 250 km was completed. This distance range is traditionally known as the zone of silence where it was believed that no energy would return to the ground surface based on classical ray theory using average atmospheric models. This study supports similar observations by others that documents the presence of signals at these distances and relates them to empirically determined atmospheric models which predict complex and multiple energy returns to the surface. In addition to quantification of these propagation path effects the explosive source strength is calibrated using a period-yield scaling relationship originally developed for nuclear explosions on the surface. Significant work conducted by the Geophysics Laboratory at Southern Methodist University since about 1993 focusing on the design, construction, installation and utilization of high performance seismic and infrasound regional arrays is documented. These designs have made significant international contributions to the field of regional seismic and infrasound monitoring for purposes of characterizing man made activities and in particular, the monitoring of a Comprehensive Nuclear Test Ban Treaty. The work described directly relates to the two studies involving infrasound phenomenology. Infrasound data observations made at the International Monitoring System (IMS) Texas array (TXAR) resulted in efforts associated with the experiments at WSMR. Seismic and infrasound observations at the IMS Nevada array (NVAR) led to the experiments concerning propagation in the zone of silence.