The Largest Earthquakes We Should Prepare for
Graduate School of Science, Tohoku University, 6-6 Aza-Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan
We should estimate the size of the largest earthquakes carefully to minimize future earthquake losses. Taking the earth’s size and the thickness of the lithosphere into account, the largest earthquakes are estimated to have a magnitude (M) of 11. The occurrence of such a gigantic earthquake, however, could wipe out the human race because energy from an M11 earthquake would be as large as the asteroid impact that is thought to have caused the extinction of the dinosaurs. This would make it meaningless to prepare for M11 earthquakes. It would be more realistic to calculate the seismic moment expected from the longest plate boundary, i.e., from the northern to northwestern boundary of the Pacific plate. The plate boundary is about 10,100 km long and the magnitude of an earthquake occurring there is estimated at approximately 10, assuming that the fault is 200 kmwide and average slip is 20 m. This means that M10 events would be the largest earthquakes we could estimate as occurring. It will not be pragmatic, however, to attempt to devise measures against such extremely rare events. It is nonetheless important to numerically simulate beforehand what might happen during such events to quickly and accurately determine the initial response to quake shaking and tsunamis.
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