STUDY ON THE EVIDENCE OF DISASTER AT THE ARCHAEOLOGICAL RUINS-EARTHQUAKE, VOLCAIC ERUPTION AND WAR

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There are many ancient remains and remnants suffered from the natural disasters. It is important to find the evidence of natural disaster at the archaeological sites, and the collaborative research is planned among natural sciences and archaeology.We studied the sand dyke at the archaeological sites. To date the sand dyke formed at the past earthquake, the archaeomagnetic method was developed. By using the method for the sand dyke at Ishizuka site in Toyama prefecture, we successfully determined the Jogan earthquake in 8th century.The sand dyke found at the Uchiide site near Toyama Bay shows the age of AD 1450 ± 50, however there have not been formerly reported earthquakes at 15th century in Toyama Prefecture. After our study, the ancient document is found which suggests the occurrence of this earthquake near Uchiide site. That is, the magnetic study clears the unknown paleo-erathquake from the archaeological sites. By the ground penetrating radar survey, the supply of sand dyke originated from the sand layer 1.5-2m under the surface plane.At the Gushikawajo castle site in Okinawa prefecture, we studied the remanent magnetization of the limestone forming stone wall of caste. The results indicate that the limestone was heated up to 350 degrees centigrade, which supports the historical evidence that the castle was burnt in a fire at the war in 16th century.At the archaeological ruins affected by volcanic disaster, to know the subjected heating influence by eruptions is valuable. Mt. Tarumae in Hokkaido is the active volcano and frequently caused the damage on the archaeological ruins of Ainu. We conducted the magnetic study on the pumice fall and/or pyloclastic flow of Mt. Tarumae at the area a few km from the crater, and found that the temperature of the eruptions at their landing is fairly high.