The Takashima-oki core boring was carried out in the central part of Lake Biwa. The core samples are composed mainly of dark greenish grey homogeneous clay sediments ranging in age from the Middle Pleistocene to Holocene. Seventyfive ashes comprising 44 distinct volcanic ash layers and 31 invisible volcanic ash horizons, are intercalated in these sediments. In order to estimate the history of explosive volcanism in the source region of the ashes, the writers divided these sediments into 8 tephro-subzones, a to h in desending order, based on lithologic and petrographic properties and frequency of appearence of the ashes. Subzones h (400 to 280 ka),f (210 to 180 ka) and c (87 to 78 ka) are characterized by the dominance of crystal ashes which consist mainly of T-type glass, feldspar and amphibole. These ashes are the products of major eruptions of the Daisen volcanic zone consisting mainly of the Daisen, Sambe and Kuju volcanoes. Subzones g (280 to 210 ka) and d (140 to 87 ka) are characterized by the dominance of vitric ashes containing abundant glass and small amounts of orthopyroxene and clinopyroxene as mafic minerals. Most of these ashes are the products of large-scale eruptions of the Kirishima volcanic zone consisting mainly of the Aso, Kakuto, Aira, Ata and Kikai caldera volcanoes. Subzones e (180 to 140 ka) and b (78 to 26 ka) are characterized by the scanty of ashes. During the deposition of these subzones, explosive volcanic activities of the Daisen and Kirishima volcanic zones are practically extinct. Subzone a (26 to 0 ka) is characterized by the occurrence of amphibole bearing crystal ashes erupted from the Daisen volcanic zone and two-pyroxene bearing vitric ashes from the Kirishima volcanic zone.

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The 1987 east off Chiba Prefecture Earthquake on December 17, 1987, caused damage in the lower reaches of the Yoro River, Ichihara city, Chiba Prefecture. The results of surveying the distribution of sand boils and the extent of damage of tiled roof in this area are summarized as follows: 1. There is a difference in the damage of tiled roof between the northeastern and the southwestern side of the Yoro River. The damage was very much heavier in the north-eastern side of the Yoro River than in the southwestern side. 2. Many sand boils occurred along the Yoro River. 3. The distribution pattern of seismic intensity and the maximum acceleration by strong motion seismographs in both sides of the Yoro River are different from each other. These facts suggest that the earthquake motion of each side of the Yoro River is independent of each other, and an active fault probably occurs along the Yoro River.

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The Kasumi Hill, one of the eleven hills which occur parallel with each other located between the Kanto Plain and the Kanto Mountains, extends east-southeastwards. It is bounded on the north by the Aki River and on the south by the Kawaguchi River. The Yajigawa River flow dawn within the Kasumi Hill along the long axis of it, and separates it into the northern and southern areas. The Yajigawa Fault occurring along the Yajigawa River is located on the extension of the normal fault which bounds the Itsukaichi sedimentary basin of Early to Middle Miocene and extends east-southeastwards. The activity of the Yajigawa Fault was probably in related to the reactivation of the Itsukaichi-Kawakami Tectonic Line which also bounds the Itsukaichi Basin, therefore the Yajigawa Fault was initially formed during Early to Middle Miocene. It is estimated that the Yajigawa Fault revived between the ages of deposition of the Miocene formation and the Plio-Pleistocene Kasumi Gravel Formation. Moreover, as the Plio-Pleistocene sediments are cut by the Yajigawa Fault in this area and is flexed or its east extension, the fault again activated in or after Plio-Pleistocene. Topographic data show the amount of recent displacement of the fault in this area increases eastwards, and the leveling data show that both of the southern and northern areas are inclinating northward, suggesting that the Kasumi Hill is presently active.

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The Pliocene Horokaoshirarika Formation of the Fukagawa Group is widely distributed around Numata-cho, 100km northwest of Sapporo. This formation is composed mainly of massive sandstones with some intercarated tuff beds. At present, 29 specimens of marine mammal fossils have been found in this formation at Numata-cho. The petrographic examination has revealed nine tuff beds except for Ops tuff in the Horokaoshirarika Formation. These tuff beds named Nt 1 to Nt 9 in ascending order are very useful to decide the stratigraphic horizons of marine mammal fossils. Tephrostratigraphy and chronology show that most of these fossils are obtained between the horizons of Ops (4.5±0.7Ma) and Nt 4 in the Uryu River and/or Nt 5 in the Horonitachibetsu River. A sirenian fossil (NFL 11) and a cetacean one (NFL 17) were found in nodules derived from the base of the Horokaoshirarika Formation. Diatom and pollen fossils from the nodules were studied to decide the geologic age and paleoenvironment. The age given by the fossil diatom assemblage of NFL 17 indicates 5.10-6.60Ma (Koizumi, 1985) which is identical with the base of this formation, whereas the age of NFL 11 indicates 7.30-9.20Ma (Koizumi, 1985). NFL 11 is considered to be derived from the underlying Shintotsukawa Group. The fossil pollen assemblage from NFL 11 and NFL 17 are characterized by a predominance of Tsuga which indicates a cool climatic condition. However, the pollen spectrum from the nodule containing NFL 17 indicates a little warmer condition than NFL 11, because of decrease of conifers and increase of temperate broadleaf trees.

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