東日本大震災のメカニズムと地震・津波の想定(<小特集>大震災から1年,今後の省エネルギー政策の方向性と節電の効果,第2回[省エネルギー,生活,「エネルギー学」三部会(LSE)セミナー])

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Future earthquakes have been predicted from past earthquakes assuming that they repeat at nearly same interval and location. Past earthquakes have been recorded by seismograms, historical documents, and sediments. Because recurrence intervals of the giant tsunamis are inferred to be longer than 500 years, only sediments can leave records of several events of tsunamis. We surveyed tsunami deposits generated by the 869 Jogan earthquake in the Sendai and surrounding areas and found that the tsunami inundated for more than 3 km from the coasts. We also constructed the source fault model of the tsunami which reached to the area of tsunami deposits distribution. The Tohoku 2011 earthquake was much larger than our Jogan model, however, the 2011 earthquake proved that the tsunami deposits are reliable warning of a future giant tsunami. Our study on the Jogan tsunami was reported to the Headquarter of Earthquake Research Promotion in 2010 and Headquarter was evaluating the possibility of a giant tsunami, but the earthquake has occurred before the issue of warning of giant tsunamis. Pacific coasts along Kanto district and SW Japan have been damaged repeatedly, and we need to prepare future earthquakes and tsunamis.
2012-10-20