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Embargoed for 1:30 P.M., EDT
NSF PR 97-41 - May 28, 1997
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Seismic Mystery Remains in Australia
Scientist-Sleuths to Report on
Latest Findings
It's a tale of Down Under, set against a backdrop
of international terrorism.
On a dark night in May, 1993, somewhere in the empty
miles of dry-as-dust Australian outback, a streak
blazed through the sky and the ground shook, according
to eyewitnesses, aborigines prospecting for gold.
In a likely script for an episode of the "X Files,"
the event happened near a ranch owned by the Japanese
cult "Aum Shinrikyo," the group accused of the poison-gas
attack on Tokyo subways in 1995. Investigators in
Australia and the United States raised concerns, at
first, that the seismicity might be the result of
cult activities. Cult followers had recently acquired
land on the outback, and were known to be mining uranium
and carrying out weapons tests there.
The U.S. Senate's Permanent Subcommittee on Investigations
became interested and requested that scientists affiliated
with the National Science Foundation (NSF)-supported
Incorporated Research Institutions for Seismology
(IRIS) in Washington, D.C., look into the incident.
IRIS scientists have been studying, ever since, seismic
recordings of the occurrence for the subcommittee.
The sleuths have concluded from seismic data -- after
ruling out a nuclear detonation -- that the earth's
trembling on that dark May night could have been caused
by the impact of a meteorite made of iron.
The scientists will present a report on their latest
findings, Earthquake Sources: Processes and
New Observations, at the spring meeting of
the American Geophysical Union, May 28, at 1:30 p.m.
at the Baltimore Convention Center.
"If the eyewitness accounts are credible," says seismologist
Gregory van der Vink, director of planning at IRIS,
"the seismic signal was most likely created by the
impact of an iron meteorite about two meters in diameter.
Such a meteorite could survive passage through the
atmosphere, and impact earth with sufficient energy
to create the seismic signal picked up by one of our
stations in the Global Seismographic Network." But,
as there is no previously known digital seismic signal
from a meteorite impact, "we have nothing to compare
this record to," adds Christel Hennet, van der Vink's
colleague at IRIS.
The IRIS scientists -- joined in their quest by researchers
Danny Harvey of the University of Colorado, Chris
Chyba of the University of Arizona, and Vipin Gupta
of Sandia National Laboratory -- estimate that only
about once every ten years does an iron meteorite
of this size survive its hurtling free-fall through
earth's atmosphere, and reach our planet's surface
intact.
"A meteorite this size would create a crater and thus
provide positive evidence of what the seismic network
readings indicate," says van der Vink. "But as yet,
no such crater has been found."
The impact of a meteorite this large would produce
a hole the size of a football field, difficult to
overlook in populous regions of the world, but perhaps
hard to find in the wide Australian outback, the equivalent
of trying to locate a contact lens in a barn. "But
we now have a good determination of the location from
analyzing the seismic records, and are working with
Sandia Labs to track it down," says van der Vink.
"We're closing in on an answer to this mystery."
If no crater can be found, says van der Vink, then
the event may have been caused by an earthquake.
If a crater is never found, and there is no credible
alternative explanation for the eyewitness accounts,
he says, "we may never know what happened that night
in a remote corner of Australia."
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Seismic readings image
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Map location of the 1993 seismic mystery
event in Australia
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