Trinity Site Atomic Blast Rocked The Seismographs

Guest Commentary
By David Medcalf

The world's first atomic bomb was exploded July 16, 1945 at the Trinity Site, on the White Sands Proving Ground (now White Sands Missile Range), 37 miles southeast of Socorro.
When the bomb exploded at approximately 5:30 a.m. MWT (Mountain War Time), the light given off was so bright it could be seen 250 miles away.
Sound waves from the blast could be heard 50 miles away. Manhattan Project scientists had an array of instruments recording the event, including high-speed cameras and radiation detectors, but another group of scientists was watching the phenomenon as well.
Harvard professor L. Don Leet was an expert at recording seismic waves from explosions and was brought to the Trinity site to record "explosion tests." For security reasons, he wasn't told what he was really supposed to measure until after he arrived in New Mexico. Leet set up a portable seismograph of his own design at San Antonio, 30 miles from Trinity. The machine's recording of the atomic blast exhibited evidence of a new type of earth motion that was later dubbed a "hydrodynamic wave." The graph also confirmed the existence of a so-called "coupled wave" which had been recorded only once before. In a 1946 paper, Leet was to write that from the test ". . . one of the most important records of earth motion in the history of seismology was obtained."
But seismologists farther afield detected the strange event as well. Seismographs at Tucson, operated by the U.S. Coast and Geodetic Survey, and at the California Institute of Technolo-gy's geophysical observatories at Palomar and Riverside, logged the episode. Using these recordings, Caltech seismologist Beno Gutenberg was able to determine the time of the detonation as 5 hours, 29 minutes, 21 seconds MWT with an error of no more than 2 seconds. This turned out to be particularly helpful because the precision timing equipment at the Trinity site had failed, leaving the time of the blast uncertain by plus or minus 15 seconds.
Gutenberg was also able to measure low frequency sound waves from the explosion using microbarographs.
The Trinity Site will be open to the public this Saturday, April 3.
Further information is available at the White Sands web site.

Medcalf is a biologist at New Mexico Tech.

Trinity Site Atomic Blast Rocked The Seismographs