The Upper Shimanto Supergroup in South Kyushu is composed of tow major fault-bounded tectono-stratigraphic units, the Hyuga Group (late Middle Eocene to Early Oligocene) on the northwest and the Nichinan Group (Late Oligocene to Earlist Miocene) on the southeast. The Hyuga and Nichinan Groups can be defined as a subduction complex and an olistostrome, respectively, and contain a thick, coherent sequences of flysch facies accumulated by deep-sea fan sedimentation. Their sedimentological features were investigated closely to reconstruct the sedimentary environments and sedimentary system of forearc region of different two stages.
The Hyuga Group is divided into three units, the Melange, Lower Flysch and Upper Flysch Units. These units are all of contemporaneous heterotopic facies, fundamentary, but differ so much in deformation facies with one another. The Upper Flysch Unit, dominantly medium-to thick-bedded sandstone, shows no synaccretionary deformations. It represents a coarsening-and-thickening upward sequence, as a whole, consisting the deposits of fan fringe, the smooth lobe, channeled lobe and/ or levee deposits, successively. Judging from the sedimentological and structural data, the Upper Flysch Unit can be evaluated convincingly to be forearc basin deposits whose sequence was developed by a process of progradation accompanied with the growing of accretionary prism toward the trench.
Among the olistoliths in the Nichinan Group, those in Late Oligocene to Earlist Miocene ages can be regarded to be the allochthonous sequences having been deposited under the shallow and the deep-marine environments in the forearc region at that time. Deep-marine flysch sequences investigated in detail on some representative olistoliths show a mudstone dominant turbidite facies, in which an asymmetric finining-and-thinning upward cycle is developed well, that begins with conglomerate or pebbly sandstone, passes into massive sandstone and interbeds of sandstone and mudstone, and ends with mudstone, typically. Sedimentological features, such as sedimentary facies, cycles and paleocurrent patterns, indicate that the sequences are inferred to be a suprafan complex, including channel-fill deposits, smooth lobe deposits, channeled lode deposits and fan fringe deposits. There are, however, many differences in lithology, thickness, sedimentary rate, paleocurrent pattern, and so on, among the olistoliths. It might be stated, therefore, that the deep-marine flysch sequences in the Nichinan Group were accumulated in the poly-axial turbidete basins and were developed by the shifting of main channels. The characteristics of such sedimentary system of forearc region are very similar to those of the California Borderland, where has been controlled by strike-slip tectonics since Oligocene.
The differences in sedimentary systems and processes between the Hyuga and Nichinan Groups may be considered to be attributed to the different tectonics of the forearc region at each stage. It appears to be correspond well to the different plate motions of the Philippine Sea Plate; the orthogonal convergence during middle Eocene to early Oligocene time, and the subsequent transform processes during late Oligocene to earlist Miocene times, respectively.

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In the study on Disaster Prevention Science, we need many data of past events to investigate the frequency, magnitude of extraordinary phenomena which have brought about serious damages to people's life through the long history.
Sedimentological method and knowledge can supply useful information about past natural disasters using the sedimentological data, such as sedimentary structures or sediment properties. Sometimes, we can explain physical processes of past events from careful analysis of the data.
Useful results of sedimentological studies for Disaster Prevention Science are shown in this paper refering to examples for studies on various natural disasters—debris flows, storms, floods and earthquakes.
Close cooperation between Disaster Prevention Science and Sedimentology is needed to study the physical processes of extraordinary events and their effects on the sedimentological environments.

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