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Possible Meteorite Fall in Australia

National Science Foundation

NSF PR 97-41					May 28, 1997

Contact:
Cheryl Dybas
(703) 306-1070/cdybas@nsf.gov

Program contact:
Dan Weill
(703) 306-1558/dweill@nsf.gov

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."

                                    -NSF-
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