On March 11, at 05:46 a.m. UTC, an earthquake of
Moment-Magnitude 9.0 occurred in the Japan Trench east of Honshu
Island. The earthquake, preceded by a M7.3 earthquake on March 9,
ruptured an area of approximately 400 km times 100 km parallel to
the coast along the interface between the Pacific and the North
American Plate. More than 300 aftershocks of magnitude 5 or higher
occurred within the following week, causing very limited additional
The earthquake is the largest recorded earthquake in the
subduction zone east of Japan. It is even one of the largest
recorded earthquakes worldwide, only exceeded by the earthquakes in
Chile (1960), Alaska (1964) and Sumatra (2004).
Despite the large distance between the rupture zone and the
coast, measured acceleration from the dense Japanese seismograph
networks K-Net and KiK-Net is around 0.5g in the coastal area
here and figure 1 below). This is in line with Japanese
attenuation functions as shown in the cited article. Nevertheless,
earthquake damage seems to be relatively limited, in many coastal
areas evidence of earthquake damage has been erased by the tsunami
induced by the earthquake.
Figure 1: Peak
ground Acceleration at the surface. The largest peak ground
acceleration among K-NET and KiK-net sites was recorded at MYG004
K-NET station, reaching 2933 gals (3 components vector summation).
(Source: NIED; National Research Institute for Earth Science and