Ahmedabad, March 13 : The 8.9 magnitude earthquake that shook Japan on Friday released energy equivalent to 336 megatons of TNT explosive, says a media report.
This earthquake is also the seventh largest in the known history of the earthquakes, says Dr J G Negi, founder director general, Institute of Seismological Research, Gandhinagar.He said that Japanese coast had tsunami waves reported to be of at least four metres.
Negi said that based on the historical records available, Dwarka in Gujarat too had experienced a tsunami of this kind once in every 500 years.
He said that normally when atmospheric motions like monsoon and motions inside the earth plates increases there is an increase in a wobble inside the earth called 'Chandler's Wobble'.
During the 2005 Java-Sumatra quake of 9.0 magnitude, there was an increase in Chandler's Wobble by 0.75 degree. The Friday Japan quake was preceded by foreshocks on March 9 of magnitude 7.2, about 40 km from the epicentre of the Friday's earthquake, and was sustained with another three earthquakes greater than magnitude 6.0 on the same day. These were precursors and must have disturbed the rotation of the earth.
It is expected that the earthquake of such a large magnitude would have precursors in the movements of Lithospheric masses. It is estimated that the 8.9 magnitude earthquake could have increased Chandler's Wobble by about 0.7 degrees. He said that a close observations of Chandler's Wobble and particularly its increase can give indication of a large quake that may be imminent.
Even in Japan's turbulent seismic history, the 8.9-magnitude earthquake that struck Friday was one for the record books.The quake—the fifth-largest recorded since 1900 and the biggest to hit Japan in three centuries—released almost 1,000 times the energy released in the Haiti quake a year ago. Friday's quake also triggered a tsunami that traversed the planet, all the way to the shores of California.
