Infrasound in the Zone of Silence
Abstract
Experiments designed to understand the propagation of infrasound signals at distances of less than 200 km were conducted in central Nevada, USA during the week of 11 September 2006. A controlled suite of explosions on the surface, designed to destroy surplus military ordnance, provided the source of the infrasound signals. Three temporary 4-element infrasound arrays were deployed in a line due north of the sources at distances from 76 to 157 km. In addition, seismo-acoustic data was provided by the permanent Nevada Infrasound Array (NVIAR) and collocated seismic array NVAR, located about 36 km east of the source. The experiment was successful, and detections from all explosions were recorded at all arrays. Therefore, the assumption of the absence of signals in the 'zone of silence' is incorrect in this case. At NVIAR the shorter distance and impulsive signals indicated the arrival of direct waves. However, other signals recorded at distances of 76 to 157 km were longer in duration, and initial travel time analysis indicated the rays were turning in the stratosphere. Simultaneous balloon launched rawinsonde weather recordings collected between the sources and the stations through the tropopause showed there were no conditions that would allow turning rays or reflections in the troposphere. Because the travel times were too short for turning rays above the stratosphere, we conclude that the energy was refracted in the stratosphere. Obviously improved atmospheric models through the stratosphere are needed to explain the occurrence of infrasound signals in the "zone of silence".
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2007
- Accession Number
- ADA519293
Entities
People
- Eugene T. Herrin
- Mihan H. McKenna
- Paul W. Golden
- Petru T. Negraru
Organizations
- Southern Methodist University