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From Project Leader
The 2011 off the Pacific coast of Tohoku Earthquake, the largest in Japanese history with a magnitude of 9.0, hit Japan on 11 March 2011. The exceptional aspect of this event was its extensive nature. Whereas earthquakes off the Miyagi prefecture and off Sanriku would previously have been expected to occur separately along the Japan trench, in this event they actually struck together. This strong quake was produced from a focal region with a length of ~500 km and a width of ~200 km wide offshore, and triggered a devastating tsunami with a maximum run-up height of 40m, that was responsible for extensive loss of life and property.
As for the Nankai Trough located off the southwest coast of Japan (i.e. close to capital territory and Chukyo and Kansai regions), Tokai, Tonankai and Nankai, earthquakes occur every 100 to 200 years and often take place either almost simultaneously, or sequentially, potentially producing several quakes of magnitude of 8.0 or above. If earthquakes occur, they could cause damage from Tokyo to Kyushu, which could exceed the entire national budget of Japan. Therefore, one of the important issues that we can put control measures in place for is the preparation for large earthquakes and tsunamis before they occur.
As part of the Earthquake and Tsunami Research Project for Disaster Prevention in JAMSTEC, the real-time seafloor observatory network system is being constructed in the focal region of the Tonankai and Nankai earthquakes and extends from Kumano-nada off the Kii Peninsula to the area off Cape Muroto. The system can capture evidence of earthquakes, crustal movements and tsunamis, contributing rapid detection and simulation study of seismic shaking and tsunami immediately after the earthquake for disaster prevention and mitigation. The processing of the collected data allows us to analyze the sub-seafloor structure in detail, investigate seismicity around the focal region, and also allows a better understanding of the mechanisms of subduction zone segmentation and seismogenesis.
Yoshiyuki Kaneda
Project Leader, Earthquake and Tsunami Research Project for Disaster Prevention