Geology, geological age, and sedimentary environment of the Nishinoomote Formation in the Kumage Group distributed in Tanegashima Island, Kagoshima, Japan were examined on the basis of detailed mapping of lithology, biostratigraphic data of radiolarian fossils and calcareous nannofossils, and ichnological analysis. Since the Nishinoomote Formation consists mainly of sandy sediments, mudstone containing large amounts of trace fossils in the middle stratigraphic interval of the Nishinoomote is newly subdivided as the Okubo Mudstone Member. The Nishinoomote Formation correlated with the radiolarian fossil zone RP20c-RP21a (31.1-28.5 Ma) and the calcareous nannofossil zone NP23-NP24 (30.00-26.84 Ma). Therefore, geological age of the Nishinoomote Formation can be considered to be late early Oligocene (30.0-28.5 Ma).

Investigation of the distribution pattern of lithology and the geological age revealed that (1) contemporaneous stratigraphic intervals in the Nishinoomote Formation repeatedly appeared due to folds and thrusts, (2) total thickness of the Nishinoomote seems to be less than 1000 m, which is thinner than those estimated by previous authors, (3) the Nishinoomote can be correlated with not the Hyuga but the Nichinan Groups distributed in Kyusyu, and (4) depositional environment for the Nishinoomote might be a sea-floor deeper than 2000 m in water depth. Further detailed sedimentological approach must be required to clarify the origin of the Nishinoomote Formation.

The stratigraphy of the Middle to Upper Pleistocene Shimosa Group beneath the Tsukuba Upland area of Ibaraki Prefecture, Kanto Plain, central Japan has been reexamined by performing detailed facies observations and analyzing intercalated tephra layers and fossil pollen assemblages in sediment cores. The Pleistocene deposits in the sediment cores are divided into five depositional cycles, each composed of fluvial and coastal sediments that formed under the influence of glacioeustacy. These cycles are correlated with the Yabu, Kamiizumi, Kiyokawa (Kamiiwahashi), Kioroshi, and Joso formations in ascending order based on the tephro- and palyno-stratigraphy. Of note, the incised valley fill beneath the Tsukuba Upland area, which was previously correlated with the Kamiiwahashi Formation (MIS 7), corresponds to the Kioroshi Formation (MIS 5e). The valley was incised during MIS 6, which was one of the most prominent sea level lowstands of the last 400 ky. The new correlation is consistent with the distribution of equivalent incised valley fills in the Kioroshi Formation beneath the Kanto Plain in Chiba and Saitama prefectures.

The 2016 Kumamoto Earthquake resulted in severe damage to houses and buildings, particularly in the central part of Mashiki Town, Kumamoto Prefecture, SW Japan. We examined drill core and standard penetration test (SPT) samples obtained from the severely damaged area to understand the influence of the underlying geology on damage caused by strong earthquake motion. The downtown Mashiki area is underlain by thick volcanogenic sediments derived from Aso volcano, comprising the Aso-3 pyroclastic flow, the Aso-4/3 interval, the Aso-4 pyroclastic flow, lahar, and loess deposits, in ascending order. The stratigraphic correlation of several boreholes in Mashiki Town reveals that the severely damaged area is characterized by a thicker fine-grained pumice bed of the Aso-4 pyroclastic flow and overlying weathered lahar deposits saturated with groundwater.

In 1997, two strong earthquakes occurred on March 26 (M_j6.6) and May 13 (M_j6.4) in the northwestern part of Kagoshima Prefecture, Japan (termed the 1997 Northwestern Kagoshima Earthquakes). However no seismogenic faults associated with these earthquakes had previously been recognized at the surface. In this study, we report structural observations from newly recognized fault outcrops located 1.5 and 2 km southwest of the epicenter of the M_j6.6 earthquake. One outcrop consists of the Miocene Shibi-san Granodiorite, which is unconformably overlain by lower sandy loam, lower humic soil, upper sandy loam, and upper humic soil layers that are clearly offset by steeply dipping faults. We measured ~ 40 cm of vertical separation of the contact between the lower sandy loam and lower humic soil layers along a WNW-trending fault, above which the ground surface flexed upward by about 20 cm. The second outcrop is a streambed exposure of the Shibi-san Granodiorite that shows a 30-cm-thick layer of foliated cataclasite along a fault plane, with textural evidence of sinistral slip.