Source location of the 19 February 2008 Oregon bolide using seismic networks and infrasound arrays

Abstract

a bolide traveled across the sky along a southern trajectory ending in a terminal burst above Oregon. The event was well recorded by the USArray, other seismic networks, four infrasound arrays, and several video cameras. We compare the results of locating the burst using these different sensor networks. Specifically, we reverse time migrate acoustic-to-seismic coupled signals recorded by the USArray out to 800 km range to image the source in 2-D space and time. We also apply a grid search over source altitude and time, minimizing the misfit between observed and predicted arrival times using 3-D ray tracing with a high-resolution atmospheric velocity model. Our seismic and video results suggest a point source rather than a line source associated with a hypersonic trajectory. We compare the seismic source locations to those obtained by using different combinations of observed infrasound array signal back azimuths and arrival times. We find that all locations are consistent. However, the seismic location is more accurate than the infrasound locations due to the larger number of seismic sensors, a more favorable seismic source-receiver geometry, and shorter ranges to the seismometers. For the infrasound array locations, correcting for the wind improved the accuracy, but implementing arrival times while increasing the precision reduced the accuracy presumably due to limitations of the source location method and/or atmospheric velocity model. We show that despite known complexities associated with acoustic-to-seismic coupling, aboveground infrasound sources can be located with dense seismic networks with remarkably high accuracy and precision.

Trajectory of the August 7, 2010 Biwako fireball determined from seismic recordings

“…Waveforms here are very similar to the waveforms of the 2002 Tagish Lake reball (Brown et al, 2002) and 1989 St. Helens reball (Qamar, 1995), which both show concentric isochrons. Similar concentric isochrones were also observed in Arrowsmith et al (2007) and Walker et al (2010). Multipathing through the atmosphere might also complicate the character of the waveforms; however, this is generally observed at distances greater than 200 km (Walker et al, 2010), which is not the range of the data in this study.…”

“…Similar concentric isochrones were also observed in Arrowsmith et al (2007) and Walker et al (2010). Multipathing through the atmosphere might also complicate the character of the waveforms; however, this is generally observed at distances greater than 200 km (Walker et al, 2010), which is not the range of the data in this study.…”

“…This distance is comparable to a difference of 32 seconds in the arrival time of the waveforms. Therefore, the extremely long duration of the signal is not necessarily unreasonable (Walker et al, 2010). Edwards et al (2008) explained that observations of explosive pointsource events tend to be diffuse, with no distinct arrival time, in contrast to the sharp onset of ballistic observations.…”

“…The location of the termination point of the signal is east of Lake Biwa, and at an altitude of 26 km. The 95% condence interval of each parameter is calculated by a bootstrap method with 100 replicates (Efron and Tibshirani, 1993;Walker et al, 2010). The uncertainties of the parameters x 0 , y 0 , z 0 , t 0 , θ are small, since the arrival time of the shock wave is sensitive to these parameters.…”

“…The airwave signal from this reball was recorded by about 50 seismic stations in Japan (NIED, 2010). This is one of the few events having an airwave signal that has been recorded by a dense seismic network (Walker et al, 2010). In this paper, we estimate the trajectory of the Biwako reball and the location of the termination point of the signal by analyzing the seismograms, and discuss the characteristic waveforms and mechanism of reball fragmentation.…”