We have compiled all the existing data about geomorphic and geologic features of the surface rupture associated with the 1945 Mj 6.8 Mikawa earthquake, which struck the eastern part of Aichi Prefecture, central Japan. The 28-km-long surface trace of the rupture, including a 10-km-long submarine section in Mikawa Bay, showed a hook-like complex shape that consisted of three sections: two N-S-trending sections comprised of the northern 7-km-long section and the southern 14-km-long section, and the other section, extending for 7 km from east to west between the two N-S-trending sections. On the basis of the compiled data and reconstructed slip distribution along the surface rupture, we suggest that 1) nearly pure thrust faulting along the southern N-Strending section was predominant among the whole surface faulting during the earthquake,2) probably, this thrust faulting was a result of E-W to ENE-WSW-trending compressional stress in the upper crust, and 3) the E-Wtrending section behaved itself as a kind of tear fault, which was an oblique-slip reverse fault associated with the nearly pure reverse faulting along the two N-S-trending sections. The maximum amount of vertical offset was approximately 200 cm.
The source fault model constructed by Kikuchi et al. (2003) includes two asperities, and the northwestern asperity covers a wider area and exhibits a larger amount of slip than the southeastern asperity does. This doesn't agree with the 1) above. Further investigations are needed to understand what causes the discordance.

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The turning of the Fukozu fault associated with the 1945 Mikawa earthquake was investigated by the present geological survey. It was ascertained that the fault had two continuous bends designated the first and third bend, and two discontinuous bends designated the second and fourth bend. Consequently the Fukozu fault is considered to be composed of three separated earthquake faults.
Judging from the formation of these faults, their major features may be explained as the results of an east-northeastward upthrusting of three land blocks on the west-southwestern sides of the faults.
These three faults are all active ones and the left-lateral displacement along the WSWENE course of the first fault (from Atsumi Bay to Maeno) has presumably accumulated in the same direction, a total distance being about 450m. Our survey, moreover, revealed that the west-southwestern extension of the WSW-ENE course of the first fault might be probably an active fault.

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The 28-km-long surface ruptures of reverse fault type were associated with the 1945 Mikawa earthquake (Mj 6.8) in the southeastern part of Aichi Prefecture, central Japan. Two traces of surface faulting had appeared along the pre-existed late Quaternary faults named as the Fukouzu (ca 18 km long) and Yokosuka (ca 10 km long) faults, showing a hook-like complex shape with N-S and E-W trending sections. All the existing data concerning the 1945 ruptures have been compiled by Sugito and Okada (2004), and then this paper describes geomorphic and geologic features, characteristics of the faults, and relationship between surface rupture and Quaternary fault.
Based on trench excavation and boring exploration surveys recently carried out at several sites by the CRIEPI (Central Research Institute of Electric Power Industry), interpretation by detailed topographic maps and air photos, leveling of fault scarplets, and age estimation for the faulted terraces, characteristics of the seismic faults have been clarified. Average vertical slip rate for the Fukouzu fault are roughly measured to be 0.6 m to 0.9 m per one thousand of years. Recurrence time of the Mikawa earthquake type is estimated about 20,000 to 30,000 yearinterval. The Yokosuka fault is a subordinate fault with weaker topographic and geologic expression and has slightly lower slip rate than Fukouzu fault. Tectonic setting, geomorphological classification and underground structure etc. in this area are also discussed.

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Diatoms are the most abundant of all aquatic living things in the hydrosphere; they are adapted to various environments and have high diversity. Here I present environmental changes in pre-historical to historical ages based on the analyses of diatom fossils from 48 archaeological sites in Japan.
I noted indicative characteri s tics of fossil diatoms, and collected them at the following sites: Tomizawa site (Sendai City of Miyagi Prefecture, Paleolithic to Kofun Periods), Matsukawado site group (Kasugai City of Aichi Pref., middle Jomon to Edo Periods), Asahi site (Kiyosu-cho and three towns of Aichi Pref., middle Jomon to Medieval Periods) and Okajima site (Nishio city of Aichi Pref., final Jomon to Medieval Periods).
In the deposits of the Paleolithic Period, I found numerous d iatoms and many insect fossils at the Tomizawa site. I reconstructed a paleogeographical map based on the appearance rate of aquatic diatoms and terrestrial diatoms. Each diatom can be separated into those that inhabited slightly above or below the ground at that time. This indicates that diatom and insect fossils did not move their living position.
Boring core samples of the early part of the Jomon Period at the Okajima and Asahi sites, include diatom fossils, mostly belonging to the inner bay or coastal diatoms, such as Cyclotella striata, Thalassionema nitzschioides, Thalassiosira spp., and Paralia sulcata Therefore during postglacial transgression, the coastal plain submerged rapidly in the early Holocene, and its coastline invaded towards the central parts of the Mikawa and Nobi Plains.
The deposits which contained a lot of brackish and marine diatoms in the late Jomon Period were found in the low land sites facing the coastal plain (Second marine transgression in the late Jomon Period). And when the Akahoya (6,300yrsBP) and the Matsukawado (3,120 ± 120yrsBP) volcanic ash layers fell, water conditions based on diatom analyses suggested a remarkable change in the water ecosystems.
Big changes of flora and fauna in the Yayoi Period are also indicated by the prolific occurrence of the paddy field diatoms and insects when the water supply system was developed nationwide for the paddy agriculture. Standardization of living things in the lowland was caused by rice cultivation in Japan. As a result of human impact on the natural ecosystem, distinct changes in the biological community occurred. From the Yayoi to Kofun Periods, saprophilous diatoms, eutrophic diatoms, coprophagous insects, saprophagous insects and parasite eggs were found from the Asahi and some other sites. These urban living things indicate the possibility of the existence of breeding animals and the concentration of people in the Asahi moated circular settlements. With the development of an agricultural society, ecological changes and environmental pollution seem to have been accelerated.
In the historical age, I found epiphytic diatoms on seaweeds in the fragments of the salt-making pottery, which educed a method of the ancient salt-making. In addition, I investigated fossil diatom assemblages in Medieval moat deposits of the Kiyosu-jokamachi site at Kiyosu town in Aichi Prefecture, which clearly showed the paleoenvironmental transition of the site.

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