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NSF PR 96-51 - September 26, 1996
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Global Neighborhood Watch
Global Seismic Network Provides 'Fail-Safe' to Nuclear Test Ban Treaty
A global monitoring system which includes stations
from the National Science Foundation (NSF)'s global
seismic network is on a global "neighborhood watch."
The United States this week signed the Comprehensive
Test Ban Treaty (CTBT), which will be verified through
an International Monitoring System. This system consists
in part of a primary and auxiliary seismic network,
which will record evidence of any nuclear testing
in violation of the treaty. The global network is
being installed by the IRIS (Incorporated Research
Institutions for Seismology) consortium and the U.S.
Geological Survey, with support from the National
Science Foundation.
Previous treaties have banned nuclear testing in all
environments except underground, but the CTBT makes
the ban complete by extending it to underground tests.
The monitoring of underground tests has been the most
controversial part of verifying the treaty.
The IRIS stations contribute not only to monitoring
of the treaty, but also to the mitigation of earthquake
hazards and scientific exploration of the Earth's
interior. "The development of such multi-use seismic
stations has created an opportunity for us to advance
our fundamental understanding of earth's structure
and dynamics while simultaneously contributing to
this important societal need," says Robert Corell,
assistant director of NSF for geosciences.
The treaty calls for a seismic network of 50 primary
stations and 120 auxiliary stations that can detect
seismic events of magnitude 4.25 and larger, and can
locate those events with an uncertainty of less than
1,000 square kilometers. (A seismic event of magnitude
4.25 corresponds to an explosive yield of approximately
one kiloton, the explosive equivalent of 1,000 tons
of TNT.) The first early U.S. weapons were in the
15-20 kiloton range, as were the first tests of the
Soviet Union, China, Britain, and India. France's
first test was about 60 kilotons. The largest test
has been about 50,000 kilotons, by the Soviet Union.
The official treaty monitoring system is in many cases
only the "tip of the iceberg" in terms of facilities
that have the potential to record seismic signals
from a secret underground explosion, according to
Greg van der Vink, director of planning at IRIS. "These
scientific resources provide the technological equivalent
of a global 'neighborhood watch' program that will
greatly enhance treaty verification."
In central Asia, for example, the Kyrghyzstan and
Kazakhstan regional IRIS network provides a detection
threshold for an area of some 10 million square kilometers
that averages about one seismic magnitude unit better
than what is required of the treaty monitoring network.
When translated to explosive yield, explains van der
Vink, this magnitude difference corresponds to a potential
detection threshold about 20 times better than that
required of the monitoring network.
In the United States, networks installed for earthquake
monitoring average two full magnitude units beyond
treaty network requirements, and are thus able to
detect explosions more than 200 times smaller than
required by the monitoring system.
According to David Simpson, president of IRIS, "More
than 50 of the stations that are part of the International
Monitoring Network required by the treaty are IRIS
stations that have already been installed as multi-use
seismic stations." They fan across the globe, from
Alaska to South America to Greenland to Europe, Africa,
Asia, Australia, and Antarctica.
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