このレポートは、Scientific American誌ブログに掲載されています。

Greetings from Drilling Vessel Chikyu! We are floating precisely at N37’ 57” E143’54”. I know we are precisely there because this unusual ship with its five working thrusters can maintain position to within meters. The sixth thruster was damaged on March 11, 2011 when D/V Chikyu, with full crew and elementary students aboard, when the tsunami caused by the Tohoku earthquake arrived at the port of Hachinohe. Thanks to quick thinking by the captain and crew, no one onboard was injured and the children were returned safely to land.

This memory is fresh in the minds of the crew and science party aboard this ship, many of whom experienced the events of March 11. The earthquake was larger than expected for this part of the coast, and the seismological community has been very active in the past 13 months revisiting everything we used to know about earthquake hazard. What’s more, the tsunami generated by this earthquake was bigger than expected ? as you have seen in the photos and videos of waves topping the seawalls in towns along the Tohoku coast. For its size, this earthquake was alarmingly effective at creating a tsunami wave.

Why? What was so special about this earthquake? Clues started emerging in the days and weeks after March 11. Japan has the most detailed network of seismometers and GPS stations, all collecting data in real time, of any country in the world. The seismometers recorded the seismic waves generated by the earthquake, and the GPS stations tracked the motion of the Japanese islands toward the deep ocean trench. Data were collected from sensors on the ocean bottom that recorded the changes in water depth related to ground deformation, ships studied the bathymetry, which showed the horizontal displacement of the edge of the North American plate toward the west.

続きはScientific American誌ブログへ