Earthquake and Tsunami in Japan

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 damage.

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 (please refer 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.

Japan_surface
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 Disaster Prevention)

References
NIED, http://www.k-net.bosai.go.jp/k-net/topics/TohokuTaiheiyo_20110311/nied_kyoshin1e.pdf