A study of acoustic propagation from a large bolide in the atmosphere with a dense seismic network

Abstract

A large meteor entered the atmosphere above northeastern Oregon on 19 February 2008 at 530 PST. Several hundreds of broadband seismic stations in the U.S. Pacific Northwest recorded acoustic‐to‐seismic coupled signals from this event. The travel times of the first arriving energy are consistent with a terminal explosion source model, suggesting that the large size of the explosion masked any signals associated with a continuous line source along its supersonic trajectory. Several infrasound arrays in North America also recorded this event. Both the seismic and infrasound data have been used to locate the explosion in 3‐D space and time. Climatological atmospheric velocity models predict that infrasound signals from sources that occur at mid‐northern latitudes in winter are usually ducted to the east due to eastward zonal winds. In this paper, we analyze travel time picks and use 3‐D ray tracing to generate synthetic travel times based on various atmospheric models to show that the seismic network data instead reveal a predominant westward propagation direction. A sudden stratospheric warming event that reversed the zonal wind flow explains this westward propagation. The seismic data illuminate in unprecedented spatial detail the range and azimuthal definition of shadow zones out to a range of 500 km, suggesting that dense seismic networks can be used to study infrasound propagation at spatial resolutions that exceed that which can be done with only a handful of globally distributed infrasound arrays.