| Description |
The University of Utah Seismograph Stations recorded 293 earthquakes (3.0 < M < 5.9) between April 17, 2007 and June 30, 2012. During this time, four-element infrasound data were collected from three permanent (NOQ, BGU, and EPU; installed 2006 - 2007) and six temporary (BRP, WMU, HWU, FSU, LCM, and PSU; installed summer of 2010) seismo-acoustic arrays. Unique epicentral infrasound observations from nine earthquakes with M 3.6 - 5.9 are identified and characterized. The detections were recorded from normal, oblique normal, and strike-slip faulting earthquakes at distances of 156 - 695 km and depths of 5 - 12 km. We use ray-tracing through ground-to- space atmospheric models from the epicenters to each array to determine the atmospheric turning altitude and associated wind velocities. Distance and wind corrected amplitudes match previously determined scaling relations. However, the duration observations from smaller magnitude earthquakes suggest the possibility of an additional scaling relation for events M < 4.6. This possible change in duration scaling relation is inconsistent with the hypothesis that infrasound duration scales with the areal extent of the epicentral region subjected to a threshold peak ground acceleration. The predicted ground motions show that the area subject to the threshold increases more rapidly with increased magnitudes. Overall, the small percentage of infrasound detections from the total possible suggests that infrasound is not a robust method of detecting and characterizing small earthquake sources. |
