On June 30th, 1908, something exploded over Tunguska, in central Siberia. Among many different effects, the Tunguska explosion produced shock waves, which were recorded by seismographs at several sites. A. Ben-Menahem (1975) made a detailed analysis of these seismic records and derived an explosive energy of 12.5 Mton. Other analyses suggested an energy value in the range 10-20 Mton. Ben-Menahem also concluded that the data on the energy source are consistent with an airburst at a height of about 8.5 km.
The explosion occurred at 0h 14' 28'' UT and devastated about 2,150 square kilometers of Siberian taigà, felling more than 60 million trees. The explosion epicenter has been localized at 60° 53' 09'' N and 101° 53' 40'' E, near the river Stony Tunguska.
Over the last ninety years this catastrophic event has inspired a plethora of scientific investigations. Despite many interesting findings, there are still substantial open questions and inconsistencies among the theories and the available data.
On July 20 - August 1, 1991, the first italian expedition, composed by M. Galli, G. Longo, S. Cecchini and R. Serra, went in Siberia. The italian researchers found several microspherules in trees, that are remnants of the Tunguska Cosmic Body (TCB). After an analysis with scanning electron microscopy (SEM), they found some chemical elements that strengthen the hypotesis of the asteroidal origin of the TCB.
On July 14-30, 1999, a second italian expedition went in Siberia in order to find scientific data, which allow to give a reasonable certainty about this event. |
