The 1968 Tokachioki Earthquake caused much damage to railway embankments built on soft subsoils. After having taken emergency action for restoration of traffic, the author started a thorough examination into the cause of embankment damage. The present paper outlines the results of the studies conducted in the first year of scheduled investigation period.

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The dams which were damaged during the Tokachioki earthquake of 1968 are small earth dams of volcanic sandy loam founded on soft sandy loam of an average thickness of 3 m. These dams were constructed before around 1920 according to the technical standards of those days. On the basis of investigations of 93 damaged dams, the damage features are classified into the following five types, and discussed from the viewpoint of earth dam design : (a) Sliding resulting in complete failure of dam(b) Sliding of upstream slope(c) Sliding of downstream slope(d) Cracking in the dam body(e) Damage to appurtenant structures

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Damage to various harbour structures caused by the 1968 Tokachioki earthquake and subsequent tsunami is described. Stability analysis was made for these structures by the current design method, and the result was compared with the actual condition of damage.According to the result of damage survey and quantitative analysis, the following conclusions were derived.(1) The feature of earthquake damage to harbour structures was, in general, not different from those observed in past earthquakes.(2) The current procedures for earthquake resistant design of harbour structures as a whole are on the fairly safe side.

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Field investigations to clarify the characteristics of liquefaction of level sandy ground were carried out at Nanaehama beach near Hakodate in Hokkaido after the Tokachioki earthquake of 1968. Three borings were carried out about three weeks after the earthquake and the results of these borings were compared with those before the earthquake. The soil stratum which was presumed to have liquefied was indentified by the proposed criteria and compared with the soil test results and photomicrographs. The hydraulic fill at Nanaehama beach underwent complete liquefaction during the Tokachioki earthquake of 1968.

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