Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Geophysics

Supervisor

Dr. Peter Brown

Abstract

We examined the far-field infrasonic signals produced by 78 bolides simultaneously detected by U.S. government sensors to determine the mechanisms responsible for interstation spreads in infrasound signal period. These signal period spreads lead to large variances in source energy estimates. Our analysis suggests that while acoustic source height contributes to some extent to the variance in signal periods, the range from the source to the station and in particular station noise plays a more significant role.

By simulating the near-field weak shocks from a suite of well-observed energetic fireballs, we have empirically estimated how often fireball shocks produce overpressure (∆P) at the ground sufficient to damage windows. Our study suggests that the effective threshold energy for fireballs to produce heavy window damage (where standard windows would have a breakage probability between 0.4 - 7%) corresponding to ∆P > 500 Pa is ~5 - 10 kilotons (kT) of TNT equivalent (where 1 kT is 4.185 x 1012 J). Such fireballs occur globally once every one to two years. The expected frequency of bolide shock waves producing heavy window damage in urban areas is once every ~5000 years. Similarly, we find that light window damage (where standard windows would have a breakage probability between 0.01 - 0.7%) for ∆P > 200 Pa is expected every ~600 years. Hence the largest annual bolide events, should they occur over a major urban centre with a large number of windows, can be expected to produce economically significant window damage.

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