New animation produced by scientists in Germany, shows that the 8.9 magnitude earthquake that struck northern Japan on March 11, was preceded two days earlier by a strong foreshock measuring 7.2 in almost exactly the same place.
Based on analysis of data provided by more than 500 sensors off the coast of northern Japan, geophysicists at Potsdam's GFZ German Research Research Centre for Geosciences have produced an animated illustration showing seismic activity before, during and after the historic earthquake on March 11, one of the strongest ever recorded.
The animation shows the earthquake activity in the region of Honshu, Japan, measured at the GFZ since 8 March 2011.
After a seismically quiet 8th March, the morning of the March 9 began with an earthquake of magnitude 7.2 off the Japanese east coast, followed by a series of smaller aftershocks.
The morning of March 11 sees a dramatic escalation of seismic activity peaking with the 8.9 magnitude quake that triggered the devastating tsunami. The earthquake is followed by many severe aftershocks, two of which almost reach the magnitude 8.
In the following days, activity slowly subsides to the point where, by March 16, relatively small magnitude 5 quakes, and a few of magnitude 6 are being registered.
The activity of aftershocks focuses mainly on the area of the March 11 earthquake. Based on the distribution of the aftershocks, scientists say, the length of the fraction of the main quake can be estimated at about 400 km. Overall, 428 earthquakes in the region of Honshu were registered at the GFZ between March 9 and March 16.
Further analysis by GFZ scientists Rongjiang Wang and Thomas Walter has found that horizontal displacements of up to five meters in an eastern direction occurred at the east coast of Japan close to the contact interface of the Pacific plate with Japan. Computer simulations of this surface show that an offset of up to 25 meters occurred during the earthquake.
Calculations of the GFZ modeling group headed by Stephan Sobolev even yielded a displacement of up to 27 meters and a vertical movement of seven meters. This caused an abrupt elevation in the deep sea, thus triggering the tsunami.