Threshold Test Ban Treaty
| Treaty on the Limitation of Underground Nuclear Weapon Tests | |
|---|---|
| Type | Arms control |
| Signed | 3 July 1974 |
| Location | Moscow, Soviet Union |
| Effective | 11 December 1990 |
| Condition | Ratification by United States of America and Union of Soviet Socialist Republics |
| Signatories | |
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The Treaty on the Limitation of Underground Nuclear Weapon Tests, also known as the Threshold Test Ban Treaty (TTBT), was signed in July 1974 by the United States and Soviet Union. It establishes a nuclear "threshold," by prohibiting tests of nuclear devices having a yield exceeding 150 kilotons (equivalent to 150,000 tons of TNT).
The threshold is militarily important since it removes the possibility of testing new or existing nuclear weapons going beyond the fractional-megaton range. In the 1960s, many tests above 150 kilotons were conducted by both countries. The mutual restraint imposed by the Treaty reduced the explosive force of new nuclear warheads and bombs which could otherwise be tested for weapons systems. Of particular significance was the relationship between explosive power of reliable, tested warheads and first-strike capability. Agreement on the Threshold Test Ban Treaty was reached during the summit meeting in Moscow in July 1974.
The treaty included a protocol which detailed technical data to be exchanged and which limited weapon testing to specific designated test sites to assist verification. The data to be exchanged included information on the geographical boundaries and geology of the testing areas. Geological data—including such factors as density of rock formation, water saturation, and depth of the water table—are useful in verifying test yields because the seismic signal produced by a given underground nuclear explosion varies with these factors at the test location. After an actual test has taken place, the geographic coordinates of the test location are to be furnished to the other party, to help in placing the test in the proper geological setting and thus in assessing the yield.
The treaty also stipulates that data will be exchanged on a certain number of tests for calibration purposes. By establishing the correlation between stated yields of explosions at the specified sites and the seismic signals produced, this exchange improved assessments by both parties of the yields of nuclear explosions based primarily on the measurements derived from their seismic instruments. The tests used for calibration purposes may be tests conducted in the past or new tests.
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