Depositional process and vegetation history from ca.40 ka to the present were reconstructed by means of tephra, facies, and pollen analyses and radiocarbon measurement for six drilling cores in Mizunashi-yachi, Komado Mire (a.s.l. ca.1,100m), Fukushima Prefecture, Northeast Japan.
In ca.40 ka, the boreal coniferous forest accompanied by Cryptomeria, Quercus, and Fagus was distributed in this area, where peat was deposited and mire was formed. The peat was partly eroded during the Last Glacial Maximum period, and subsequently it began to deposit again at ca.18.5 ka. Between ca.18.5 ka and ca.16.4 ka the forest dominated by Betula admixed with boreal conifers was distributed in the surroundings. Cool temperate deciduous broad-leaved forest dominated by Quercus and Fagus expanded under the microtherm climate between ca.16.4 ka and ca.15.6 ka, but Betula forest expanded again between ca.15.6 ka and ca.14.3 ka. The time period during which Betula forest expanded corresponds to the Younger Dryas cooling event in the North Atlantic region. After that, Betula forest reduced gradually and was replaced by cool temperate deciduous broadleaved forest composed mainly of Fagus and Quercus. Since ca.1.3 ka, Cryptomeria japonica forest has expanded.

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A large amount of sediments was taken from the horizon stratigraphically equivalent to the artifact layer in the Xiaochangliang site, an important archaeological site of Early Pleistocene age. The sediments were washed with fine-mesh screens to collect small mammal remains. The layer is dated as 1.36 Ma by paleomagnetic measurements. Small mammal remains are important for biostratigraphic and paleoenvironmental studies, but they have been hardly collected from the site before the present study. A large number of the remains collected by the screen-washing have revealed the characteristics of the small mammal fauna of the site. The fauna is compared with those of the four well-dated localities in the adjacent area. On the basis of the faunal characteristics and comparisons, we discuss the biostratigraphy and faunal turnover in the Late Pliocene and Pleistocene. Furthermore, we reconstruct the paleoenvironment around the site in the Early Pleistocene.

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The Asashiro Tephra Bed in the lowermost Osaka Group was correlated to the Tzw Tephra Bed in the Nishiyama Formation in the Niigata region based on their horizon, petrography, and chemical composition of glass shards. Thus, the distribution of Asashiro-Tzw Tephra Bed was confirmed widely in central Japan from Awaji Island to Tainai area in the northern Niigata region. This tephra bed is intercalated in the uppermost Gauss chronozone. The age of this Asr-Tzw Tephra Bed is suspected to be 2.6 Ma or somewhat older. This widespread tephra bed is expected to be useful to detect the Gauss-Matuyama boundary (GMB) over a wide area in Japan.

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In order to clarify the activity of the Tachikawa fault during the Quaternary, four boring cores collected by boring surveys conducted at Mitsugi in Musashi-Murayama City and Hakonegasaki in Mizuho Town, the western part of the Musashino uplands, Tokyo metropolitan area, were reexamined. Also, a geological survey in the Sayama hills was carried out. The transection along the MTB1 Core on the downward side, Musashi-Murayama Core on the flexure scarp, and MTB2 Core on the upward side crosses the Tachikawa fault in Mitsugi district. Sediments, composed of gravels, sands, silt, and peat, correlative to the Kazusa Group (early Quartenary strata), are overlain by terrace deposits and the Sagami Group. These sediments contain many tephra layers. Several tephras are identified, as follows.
MTB1-9 to MTB1-10L (MTB1 Core) and MM-8 to MM-8.2 (Musashi-Murayama Core) are correlative to SGO identified within the Sayama Formation in the west part of the Sayama hills. MTB1-22 and MM-12 are correlative to SYG (1.7 Ma) in the northwest part of the hills. A tephra group composed of three tephras (MM-21.1, -22, and -24 in Musashi-Murayama Core and MTB2-21.5, -22, and -24.5 in MTB2 Core) is found at the westernmost part of the hills, and is defined as the Hakonegasaki Tephra Group here. Two widespread tephras, Ebs-Fukuda (1.75 Ma) and Tmg-R4 (2.0 Ma), are identified in the MTB1 Core (MTB1-26) and MTB2 Core (MTB2-26), respectively. Kd44 (1.968-1.781 Ma) in the Kazusa Group, Boso Peninsula, is correlated with MM-18 in Musashi-Murayama Core and MH-3 in the Mizuho Core. Altitudes of SYG show northeast-side-up offset with an accumulated deformation of ca.126m. No cumulative deformation of the strata between SYG and the Hakonegasaki Tephra Group (ca.2.0 Ma) was detected, indicating that the fault was not active during the period from 2.0 Ma to 1.7 Ma. The timing of initiation of the Tachikawa fault (<1.7 Ma) will be determined in detail by the further study of SGO.
The Tachikawa fault is composed of the Southeast segment, 15km long, and the Northwest segment, 3km long. The Mizuho fault, recognized by the previous underground survey, is most likely to be the southeast part of the Northwest segment, showing an en-echelon structure running in parallel a distance of ca.1.5km.

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Geotechnical properties of Holocene and latest Pleistocene unconsolidated sediments were statistically investigated in correlation with shear wave velocities accurately measured in boreholes using the PS suspension logging tool. The geotechnical data, collected from two regions, more than 200 boreholes, and 9,000 depth points, comprise N-values obtained by in situ Standard Penetration Test (SPT), bulk densities, solidities, and median grain sizes measured by the standard laboratory test, and the elastic constants determined by tri-axial dynamic loading tests. Recent advances in sedimentological research have revealed detailed lithofacies of the Holocene and latest Pleistocene sediments of the southern part of the Kanto Plain and the coastal region of the Nobi Plain based on comprehensive core investigations. The revealed lithofacies were taken into account in the correlation analysis.
The results of the correlation analysis are as follows. First, natural water content ratio and void ratio are inappropriate as an indicator of lithofacies or geotechnical properties because the parameters are defined as the relative ratio to the solid weight or to the solid volume. Instead, bulk density and solidity (the complement of porosity) are practical as such indicators. Second, ambiguity still remained in the statistical relationship between N-values and S-wave velocities even when we used high precision S-wave velocity data obtained using the suspension logging tool. This means the ambiguity is mainly attributed to the poor quality of N-values. So it is possible to estimate N-values from S-wave velocity data using an empirically synthesized equation, but it is very hard to estimate S-wave velocities from N-value data. Third, a clear relationship was recognized between S-wave velocities and solidities or bulk densities, and it seemed to vary with lithofacies and depositional stage. This indicates that S-wave velocity itself is helpful as a good indicator to evaluate other geotechnical properties of Holocene sediments and to estimate the sedimentological environments.

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