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Geology and the Seismic Test Ban System

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trinitite

Trinitite: fused desert sand from the first atomic bomb test.

Photo (c) Andrew Alden, licensed to About.com (fair use policy)

The atomic age began on 16 July 1945, and atomic warfare began three weeks later. In the decades since then, thousands of nuclear explosives have been tested. There's a map on the Web that shows where the bombs were deployed and who exploded them: the dots scattered around the world's remote places look no different from the two dots in populated southern Japan. And for millions of citizens, thousands of activists and hundreds of disarmament negotiators, every new dot during those years was just as much a threat to peace as those two over Hiroshima and Nagasaki.

Finally, in 1996 the Comprehensive Nuclear Test Ban Treaty (CTBT) was wrapped up and quickly signed by a large set of countries. As of 2009, 180 nations had signed it and 148 of those had formally ratified it. A crucial part of the treaty is watching everybody to ensure that there are no cheaters. The watchers are geologists.

The Seismic Forensic Solution

Seismic networks have always been a part of the Cold War—indeed, once it was learned exactly how deep explosions differ from ordinary quakes, the military was a constant presence in earthquake studies. Now the spies have come in from the cold, military and civilian programs have been consolidated, and a large international seismic network has been set up. This nuclear "neighborhood watch," part of the International Monitoring System (IMS), is able to hear an explosion of one kiloton, and pinpoint it to within about 40 kilometers, anywhere on Earth.

The IMS will have some 170 seismic stations (50 primary and 120 auxiliary), and will coexist with three other networks: 80 air-sampling stations that will detect radioactive byproducts of any nuclear test, 11 sets of ocean-mounted hydrophones, and 60 atmospheric stations to pick up the infrasound made by explosions. All of the data—and this is where the envelope gets pushed—will be sent in real time to a central facility, open to anyone in the world. An excellent introduction to the whole system is on the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) site.

The Promised Network

While the diplomats were dickering all those years, an international group of scientists was testing the network that will be needed.

President Clinton, representing the first nuclear nation, was the first to sign the CTBT, and during his adminstration the United States had the largest Web sites related to its role in the IMS. The seismic data from many stations flowed through a national data center at the Air Force Technical Applications Center (AFTAC) in Florida, where they could be shared with scientists and institutions worldwide. These seismic measurements, as well as more data from the air-sampling, hydroacoustic, and infrasound networks, were to flow to the central repository or International Data Center (IDC).

The U.S. Senate failed to ratify the CTBT in 1999, and the Bush administration stopped progress on the plan. As a candidate, Barack Obama promised to end the freeze as soon as practicable, but no action has been taken as of mid-2011.

The majority of the seismic network has already been emplaced by the international earthquake consortium IRIS (Incorporated Research Institutions for Seismology), the U.S. Geological Survey, and the National Science Foundation. We are building a global set of ears-to-the-ground that while ensuring nuclear verification for the future will also be ready to collect high-quality earthquake data. The cause of peace will, in time, pay huge dividends for science.

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