seismic explosion
Soldiers monitoring a seismic explosion from a distance, Jan. 26, 2011. Photo by Eliahu Hershkovitz
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The Geophysical Institute of Israel carried out a controlled explosion using 100 tons of explosives Wednesday morning in order to calibrate the instruments of acoustic stations that monitor nuclear testing throughout the world.

The explosion, carried out at the Israel Defense Forces' ground forces testing site in the Negev, is the largest controlled explosion ever conducted in Israel. It created a mushroom cloud that, according to preliminary measurements, reached a height of two to three kilometers, and sound waves that carried some 6,000 kilometers and could be measured at testing stations in Russia, Kazakhstan and even Mongolia.

All these countries are part of the International Monitoring System created after the 1996 adoption of the Comprehensive Nuclear Test Ban Treaty. Their stations provide data about nuclear testing that has gone unreported to the United Nations and the international community.

There are dozens of such monitoring stations worldwide, in Africa, North America, South America, Asia and Europe. A controlled explosion like yesterday's, with a known quantity of explosives, allows accurate calibration based on known data.

The data was broadcast to them in real time from equipment placed up to 100 meters from the blast site that measured pressure and other parameters. The stations then broadcast the data instantaneously, by satellite, to the international data center in Vienna for analysis.

The blast, which measured 2.7 on the Richter Scale, was also detected by seismic stations throughout Israel.

According to Dr. Yefim Gitterman of the Geophysical Institute, acoustic waves cross great distances because they first rise to a height of some 100 kilometers and are then borne on stratospheric winds.

In a similar explosion conducted last year, the acoustic waves moved mainly toward Europe and reached as far as France.

The scientists and military officials who conducted the test observed it from a bunker six kilometers away. At another observation point in an open area nine kilometers away, visiting scientists from institutes in the United States and France, soldiers from the nearby base, journalists and students were able to observe the impressive cloud of smoke that bloomed from among the hills in complete silence, followed only some 25 seconds later by the sound of the blast.

The explosion created a crater 20 meters in diameter and four meters deep.

Researchers from various fields were interested in different aspects of the test. Geophysical researchers climbed into the hole to study the rocks, while weapons specialists had pulled out advanced sensors from the soil. Scientists from Ben-Gurion University, in cooperation with the IDF, had built two bunkers some 100 meters from the blast point to study the structures' durability.

Prof. Gabi Ben-Dor, dean of the Faculty of Engineering Sciences at Ben-Gurion and head of its center for the development of protective technology, said the IDF wants to test the durability of its weapon storage sites.

Dr. Rami Hofstetter, head of seismology at the Geophysical Institute, said the experiment was also important because learning how acoustic wave travel will make it possible to distinguish the waves produced by earthquakes from those produced by explosions, and thus to build a precise historical catalog of earthquakes in order to calculate seismic risks.