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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy<br />

(S) - <strong>IASPEI</strong> - International Association of Seismology and Physics of the Earth's<br />

Interior<br />

JSS002 Oral Presentation 1737<br />

Geology and archaeology evidence of megatsunami impact in Easter Island<br />

from tsunamigenic tectonic event in Southern Chile: May 22, 1960 (M 9.5)<br />

and December 16, 1575 (M 8.5) Earthquakes<br />

Prof. Oscar Gonzalez-Ferran<br />

GEOLOGY AND GEOPHYSIC UNIVERSITY OF CHILE IAVCEI<br />

Cortez Carolina, E .Lorca, E .Zarate, R Mazzuoli, S .Rapu<br />

Easter Island (2709S / 10926W) one of the most isolated land in the Earth at the southeastern Pacific<br />

Ocean, famous for the giant megalitic monument of the Rapa Nui culture, building during the century<br />

XIII XVII, declared by UNESCO as a World Heritage Site since 1995 , had been the most important and<br />

the best elements for register and preservation some geophysical hazard in the past, as earthquakes,<br />

tsunamis and landslide. Into the archaeological ruins, we have been recognise two main groups of<br />

Ahus: the oldest semipiramidal which represent to hoard up ruins; and the youngest ahu-moai, the<br />

biggest and mainly collapsed by earthquakes. The Island is entirely compound by young volcanic rocks,<br />

characterized by a rough triangular shape with 160 Km2, represent the small emerged portion of the<br />

large submarine volcanic complex, that rise from about 3000 m. over the oceanic Nazca plate.<br />

Geological and geophysics hazard research along the coast perimeter of the island, which is<br />

characterized by the high cliff at the three volcanic corner, and about 70% flat and broadly beaches of<br />

basaltic lava flows without sand, where are developed a sequence of small rocky pocket beaches, inlets<br />

and boulder-blocky-pebbles in the marine abrasion zone, which are quite narrow. On this coast line,<br />

where set up about 90% the biggest megalithic monuments. We discover the enormous impacts caused<br />

by the big mega tsunamis occurred in May 1960 and December 1575, not only for the geological<br />

evidences as a great amount of marine detritus deposit run up along the southeastern coast and strong<br />

erosion of the Poike volcano cliff, also for the huge catastrophic impact to archaeological ruins of AHU<br />

MOAI by the 1960, and double impact to the AHU SEMIPIRAMIDAL by the 1575 and 1960 tsunamis.<br />

The measure the inundation areas, the variation of the high wave, where maximum was estimated<br />

about 30 m. high near the Poike cliff-Tongariki valley and 10 to 15m. toward southwest and the run up<br />

characteristics deposits variables between few meters and near one kilometre in land and also remove<br />

big moai which weight more than 40 ton.. and many basaltic block more than 6 ton, for hundred meters<br />

in land. These research had give an important information about the magnitude of these two mega<br />

tsunamigenic impact in the Easter Island, located about 4500 kms. north west from the earthquakes<br />

epicentre at the subduction zone in southern Chile. We present here six sections: Tongariki; Hanga<br />

Maihiku; Hanga Tetenga; Akahanga-Ura uranga Te Mahina; Koe-Koe and Hanga Poukura-Hanga Tee.<br />

Five of them were lucky not have been remove by archaeologist and conserved unaltered the tsunamis<br />

and earthquakes evidences through time, complemented with photographic documentation before and<br />

after the events. On the base these information we present the Tsunami Hazard Chart for Easter Island,<br />

which also is correlated with the tsunami numerical modelling techniques from distance.<br />

Keywords: easter island, megatsunami archaeotsunami, field survey data hazard map

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