New Zealand Journal of Geology and Geophysics abstracts
Seismic detection of the 7 July 1999 Hawera fireball
V. Manville*
S. Sherburn
Institute of Geological & Nuclear Sciences Ltd
Wairakei Research Centre
Private Bag 2000
Taupo, New Zealand
*email: v.manville@gns.cri.nz
T. Webb
Institute of Geological & Nuclear Sciences Ltd
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract In the afternoon of 7 July 1999, a meteor estimated
to weigh up to 10 tons entered the Earth’s atmosphere to the northwest
of
New Zealand. Visual observers between Whangarei and Timaru reported the path
of the fireball across the sky, before it exploded c. 33 km above the small
Taranaki town of Hawera. United States Department of Defence satellites detected
the terminal blast at 04:14:42 UTC (c. 4:14 p.m. local time). This detonation
produced a quasi-spherical atmospheric shock wave that weakly coupled with
the ground, generating a signal that was recorded by 18 seismograph stations
that form part of the geological hazards monitoring network operated by the
Institute of Geological & Nuclear Sciences. Modelling of arrival times
of the sonic boom at a subset of stations constrains an explosive point source
location to 39.45°S, 174.45°E, at an elevation of 32 km, which places
the explosion 20 km northeast of Hawera. Minimum source energy of the terminal
blast is estimated at c. 0.3 kiloton from inversion of the zone of audibility
of the explosion. Although optimised for the monitoring of terrestrial geohazards,
New Zealand’s seismic stations have also shown their utility in detecting
extra-terrestrial phenomena.
Keywords meteor; bolide; seismic network; shock wave
G02063; Received 2 December 2002; accepted 19 December 2003; Online publication
date 20 May 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 269–274
0028–8306/04/4702–0269 © The Royal Society of New Zealand 2004
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