At press events Wednesday, two groups of scientists will present their views on the science of the Comprehensive Test Ban Treaty (CTBT) which goes up for a ratification vote next week.

In order to test nuclear weapons without firing them, as required by CTBT, scientists rely on a combination of complex computer modeling programs and sub-critical tests. Data is taken from different parts of the nuclear device, and run through a super-computer, which helps scientists predict how parts of the nuclear device will behave.

Scientists also model the shape, materials, electrical systems and chemical operations present in a nuclear weapon. The model is then subjected to the physical forces it might encounter if were detonated or involved in an accident.

Scientists can look at the components before and after detonation and see if the weapon behaves as it is designed to. Then, to ensure that the results being produced by the computer are accurate, scientists compare the computer simulations with prior nuclear, and non-nuclear (sub-critical), tests. This allows scientists to test the efficacy of nuclear weapons, without having to do additional nuclear testing.

Another consideration is how to monitor possible nuclear testing by other countries in violation of the CTBT. The treaty calls for 170 seismic monitoring stations, which will be set up to detect seismic activity underground. The seismic network is designed to monitor seismic events worldwide, both natural and man-made, that have a magnitude of 4 or greater (a one kiloton explosion creates a seismic event of roughly 4 on the Richter scale). In many areas of monitoring concern, the detection threshold is actually much lower.

Looking at the type of seismic waves that make up an event, scientists can determine where the event was located, and whether it was an explosion, or a natural occurrence like an earthquake.

There are two types of seismic waves, compression waves, and shear waves. By calculating the difference in the times that the compression and sheer waves arrive at the sensor (compression waves travel faster) scientists can determine how far away the seismic event was. Then, using additional sensors (sometimes far from the original event), scientists can triangulate the location of the seismic activity. To determine whether the seismic event was natural or man-made, scientists look at the strength of the seismic waves. Explosions produce stronger compression waves, whereas earthquakes produce stronger shear waves.

Two separate events will take place Wednesday, October 6th in Washington, D.C. related to the Comprehensive Test Ban Treaty.

1)Wednesday, October 6, 1999
10:00 am EDT
American Geophysical Union
2000 Florida Avenue NW
Washington, DC 20009

The American Geophysical Union and the Seismological Society of America will hold a press conference to announce a position statement on the capability of monitoring the CTBT. It will take place at AGU headquarters in Washington. Scientists will be available to answer questions.

2) Wednesday, October 6, 1999
3:00pm EDT
East Room
The White House

An unprecedented number of Physics Nobel Laureates have come together in a single statement supporting the Comprehensive Test Ban Treaty and the reliability of simulated testing of nuclear weapons. A representative group will be at the White House event to read their statement, which was sent to every member of the US Senate on Tuesday.

Press interested in attending either of these events should contact AGU or the White House directly.

Harvey Leifert
American Geophysical Union
(202) 777-7507

White House Press Office
(202) 456-2580