Most of offshore constructions use the natural ground (alluvial clay layer) as a landfill bottom liner. The Ministerial Ordinance Determining Engineering Standards Pertaining to Final Disposal Site for Municipal Solid Wastes and Final Disposal Site for Industrial Wastes (Ordinance No.1 of the General Administrative Agency of the Cabinet and the Ministry of Health and Welfare, 14^th March, 1977) provides that the landfill bottom liner must have suitable liner structure.
 Therefore, knowing the settling phenomena of landfilled wastes is very important in case of analyzing influences of offshore constructions to the surrounding environment. However, little research had been carried out to investigate the effect of waste dumping on the landfill bottom liner so far, and it's not so easy to grasp actual phenomena. It is the major reason that the presence of suspended solids in water interferes the observation of such phenomena. So, we have tried to know the settling phenomena of landfilled wastes by using sonar exploration (i.e., side imaging sonar).
 As a result, images obtained by the sonar exploration enabled to know the settling phenomena of a swarm of solid particles, then the possibility to know the change of seabed shape was revealed. In conclusion, the observation by using the sonar exploration can be a useful method in the management of waste dumping for offshore constructions.

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 We conducted a trench excavation and array drillings on the northeastern part of the Eastern Ube fault, in order to reveal the fault activity in central-southern Yamaguchi Prefecture.
 A fault thrown down to the southeast was found at the trench wall. By combining the trench survey results with previous studies, we showed that the latest and the penultimate events of the fault occurred in a period from 11,500 to 400 years ago and 38,000 to 20,000 years ago, respectively. Accordingly, the recurrence interval of the fault ranges from 8,500 to 37,600 years. No fault could be detected by the array drilling survey.

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 We examined the relationship between the Absolute Ages and the Compression Strength of the sandstones and the mudstones in the Miyazaki Group. As a result, we prove the compression strength increase rate of the sandstones is larger than that of the mudstones.
 And we can achieve the economically design of engineering works but the according uneconomical design of civil structure by the relationship between the Absolute Ages and the compression strength in the Miyazaki Group.

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