Seismic Precursors to Space Shuttle Shock Fronts

--Seismic precursors to space shuttle re-entry shock fronts are detected at TXAR in Southwest Texas when the ground track of the orbiter vehicle passes within 150-200km of the observatory. These precursors have been termed "shuttle-quakes" because their seismograms superficially mimic the...

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Bibliographic Details
Published in:Pure and applied geophysics 2002-03, Vol.159 (5), p.1153-1181
Main Authors: Sorrells, G., Bonner, J., Herrin, E. T.
Format: Article
Language:English
Subjects:
Bow waves
Earthquakes
Geophysics
Horizontal
Phase velocity
Precursors
Seismic activity
Seismic engineering
Seismic phenomena
Seismology
Shock fronts
Space shuttle
Space shuttles
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Summary:--Seismic precursors to space shuttle re-entry shock fronts are detected at TXAR in Southwest Texas when the ground track of the orbiter vehicle passes within 150-200km of the observatory. These precursors have been termed "shuttle-quakes" because their seismograms superficially mimic the seismograms of small earthquakes from shallow sources. Analysis of the "shuttle-quake" seismograms, however, reveals one important difference. Unlike ordinary earthquakes, the propagation azimuths and horizontal phase velocities of the individual phases of the "shuttle-quakes" are functionally related. From a theoretical model developed to account for the origin of these precursors it is found that the seismic phases of "shuttle-quakes" are "bow" waves. A "bow" wave originates at the advancing tip of the shock front trace (i.e., intersection of the re-entry shock front with the surface of the earth) when the ground speed of the orbiter vehicle exceeds the horizontal phase velocity of a particular seismic phase. "Bow" waves are shown to differ in two important respects from the ordinary seismic phases. They vanish ahead of the advancing tip of the shock front trace and their propagation azimuths and horizontal phase velocities are functionally related. The ground speed of the orbiter vehicle exceeds the horizontal phase velocities of crustal seismic phase over much of the re-entry flight profile. As a result, P,S, and R ^sub g^"bow" waves will be seen as precursors to the re-entry shock front at stations located within a few hundred km of its ground track.[PUBLICATION ABSTRACT]
ISSN:0033-4553
1420-9136
DOI:10.1007/s00024-002-8676-0