Large Size and Large Slip of the 2011 Tohoku Earthquake

The Tohoku area is very active seismically, but the huge size of the 2011 event was unexpected. This included the very large slip on the shallow portion of the fault that generated the devastating tsunami. Also, the sources of high- and low-frequency energy have distinctly different locations, which affect the character of the strong motions. The earthquake was quickly detected by the Early Warning System which quickly issued alerts of the severe shaking.