Threshold Test Ban Treaty (TTBT)

The Threshold Test Ban Treaty (TTBT) of 1974, formally known as the Treaty on the Limitation of Underground Nuclear Weapons Tests, establishes a nuclear "threshold" by prohibiting nuclear tests of weapons having a yield of more than 150 kilotons (150,000 tons of TNT). It was signed by the United States and the Soviet Union on July 3, 1974. The TTBT was a companion treaty to the Peaceful Nuclear Explosions Treaty of 1976.

Verification

The Treaty restricted weapons testing to defined nuclear sites to help with verification. It included a Protocol which outlined technical information to be exchanged, including the geographical boundaries and geology of the testing sites. According to Section 1 of the additional verification Protocol, the following information will be exchanged between the two nations:

1. The geographic coordinates of the boundaries of each test site and of the boundaries of the geophysically distinct testing areas therein.
2. Information on the geology of the testing areas of the sites (the rock characteristics of geological formations and the basic physical properties of the rock, i.e., density, seismic velocity, water saturation, porosity and the depth of water table). Geological data can be used to verify test yields because the seismic fingerprint produced by a given undergroud nuclear explosion varies with geological factors.
3. The geographic coordinates of underground nuclear weapon tests, after they have been conducted. After every test, the geographic coordinates of the test location are to be given to the other party.
4. Yield, date, time, depth and coordinates for two nuclear weapon tests for calibration purposes from each geophysically distinct testing area where underground nuclear weapon tests have been and are to be conducted.

The Threshold Test Ban Treaty calls for open communication between the two nations. The Coordinating Group was set up as the forum for resolving disputes and ensuring correct implementation of the Treaty.

The Coordinating Group meets to oversee implementation of the Threshold Test Ban Treaty. The Soviet delegation sits on the left; the US delegation is on the right. The Group met from February-March 1991.

History

The first proposal for the cessation of nuclear weapons testing was made in 1955. The first major negotiations with the Soviet Union were held in 1958 with the participation of the United Kingdom. During the 1960's, many tests of over 150 kilotons were being conducted by the US and the Soviet Union. The 100 megaton Tsar Bomba, detonated in 1961 by the Soviet Union, was the largest nuclear explosion ever to occur on Earth.

In 1963, the Partial Test Ban Treaty was signed by the USSR, the US, and the UK. It prohibited nuclear weapons testing in the atmosphere, in outer space, and underwater. However, underground nuclear explosions were not expressly prohibited by the PTBT. In the spring of 1974, the US and the Soviet Union agreed to pursue further restrictions on nuclear weapons testing. A delegation of US experts was sent to Moscow for technical negotiations.

During the summit meeting in Moscow oof July 1974, agreement was reached on the Threshold Test Ban Treaty. It was signed on July 3, 1974.

Although the treaty was not ratified for many years, both nations agreed to observe the Treaty-defined limit of 150 kilotons for nuclear tests. After the an additional verification Protocol was agreed upon in June 1990, both nations ratified the Treaty. It entered into force on December 11, 1990, along with its companion treaty, the Peaceful Nuclear Explosions Treaty (PNET).