This review focuses on research on tsunami deposits using flume experiments, summarizing current progress and future perspectives. Sedimentary conditions are easily controlled in flume experiments, and this allows insights into the sedimentary processes that occur during tsunami flow. Previous studies using flume experiments have provided an important input into numerical models of tsunami sediment transport. However, additional experimental studies are required to improve the identification and interpretation of tsunami deposits in the geological record. Recent studies, such as flume experiments that focused on terrestrial topography and large-scale flume experiments that enabled the recognition of sedimentary structures, have improved our understanding of sedimentary process associated with tsunami deposits.

The subsurface structure of active faults can be investigated using electrical resistivity data. We conducted an audio-frequency magnetotelluric survey across the western segment of the Biwako Fault in the Yamasaki fault zone, southwestern Japan, yielding the two-dimensional resistivity structure to a depth of 1.5 km. Our resistivity structure model is characterized by a near-surface conductive layer, laterally continuous conductive zones (350-500 m depth), and two conductive zones (900-1400 depth). The deeper conductive zone is located between the western segment of the Biwako Fault and the northwestward extension of the surface trace of the eastern segment of the fault, suggesting that the eastern segment extends northwestward, as a concealed fault, nearly parallel to the western segment. Our model for the Biwako Fault is significantly different to the resistivity structure model of the Hijima Fault, which shows shallower conductive zones beneath the surface fault traces and a different spatial distribution of deeper conductive zones. The discrepancy is likely associated with different subsurface geology, different patterns of fluid supply, and local changes in the stress field governed by fault geometry.

We report a newly discovered Paleoproterozoic granitoid at the northern margin of the Maizuru Terrane (Tsuwano area, southwestern Shimane Prefecture, SW Japan). The granitoid is associated with metadolerite and metagabbro, and appears as lenticular blocks within a narrow (150-300 m wide) zone. Orthogneiss and tonalite-quartz diorite from the granitoid yield zircon U‒Pb ages of 1836±17 Ma and 1853 ± 14 Ma, respectively. Younger U‒Pb ages of 415.2±2.5 Ma were obtained from a granodioritic lithology. The Paleoproterozoic zircon grains commonly contain inherited older (2800‒2100 Ma) cores. The Paleoproterozoic age of the granitoid body supports the suggestion that this part of the Maizuru Terrane includes exotic blocks that originated from the North China Craton. The younger (Early Devonian) granodiorite is possibly related to igneous rocks of similar age from the Maizuru‒Oe area (Northern Zone of the Maizuru Terrane). Based on the lithology and structural position of the Paleoproterozoic rocks, it is suggested that they are part of the Northern Zone. The recognition of a narrow zone of Paleoproterozoic rocks embedded in Permian strata is in contrast to the nappe structure in SW Japan, which typically contains older units at higher structural positions. We therefore suggest that the Paleoproterozoic blocks were displaced by strike-slip faulting along the northern boundary of the Maizuru Terrane.

Magma processes associated with plutonic rocks are known to involve fractional crystallization, assimilation with crustal materials, and magma mixing and/or mingling with coeval intrusive rocks. We studied such processes in the Yanai region, in the western part of Yashiro-jima Island and the Murotsu Peninsula (Yamaguchi Prefecture). In this area, the Gamano granodiorite and high-grade rocks of the Ryoke metamorphic belt are exposed. Field relations and geochronological data indicate that the emplacement of the Gamano granodiorite occurred simultaneously with peak metamorphism. We identified four lithologies in the Gamano granodiorite (biotite granodiorite, garnet granodiorite, hornblende granodiorite, and biotite granite). The main facies is the biotite granodiorite, whereas garnet granodiorite and hornblende granodiorite occur around the pelitic gneiss and coeval diorite, respectively. The garnet granodiorite contains zoned garnet crystals, characterized by an almandine-rich core, possibly derived from pelitic gneiss xenocrysts, and a spessartine-rich rim, which was crystallized from the granitic magma. Mixing and/or mingling microscopic textures are recognized in the hornblende granodiorite. The initial values of Sr-Nd isotopic ratios support the idea that the garnet granodiorite and hornblende granodiorite interacted with the pelitic gneiss and the diorite, respectively. The biotite granite, which is the fourth lithology in the Gamano granodiorite, is recognized as small stocks intruding into the biotite granodiorite. Geochemical variation diagrams show overlapping trends of the biotite granite and biotite granodiorite. In addition, these two lithologies show similar isotopic compositions. Based on petrological considerations, it is suggested that the garnet granodiorite was produced by assimilation of the biotite granodiorite magma with the host pelitic gneiss. In contrast, the hornblende granodiorite was likely produced by magma mixing and/or mingling between the biotite granodiorite and the diorite magmas. The biotite granite likely represents an evolved magma derived from the biotite granodiorite.

The aim of this study is to addresses unresolved issues associated with the depositional and metamorphic ages of the Sanbagawa metamorphic rocks (central Shikoku, Japan). We performed laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb analysis on psammitic schists from the Sanbagawa metamorphic rocks (sensu stricto) in the Besshi-Asemi-gawa region. Young U-Pb ages of ca. 100-90 Ma were found in all analysed samples, regardless of the metamorphic grade. These results suggest that the Sanbagawa metamorphic rocks from the upper chlorite to oligoclase-biotite zones are metamorphic equivalents of the Cretaceous Northern Shimanto accretionary complex, which also underwent prograde metamorphism after ca. 100-90 Ma. Based on our results and previous geochronological data from the Sanbagawa metamorphic rocks, we suggest that the Sanbagawa metamorphic belt consists of three metamorphic units, which are characterized by different depositional and metamorphic ages. These three units, from old to young, are here referred to as the Besshi, Asemi-gawa, and Oboke units.

Small olivine-norite bodies crop out along the Ougon-douro, southern part of the Hidaka metamorphic belt. This outcrop has been visited by many geological excursions since the 1970s. However, the geological relations with the adjacent igneous rocks were unclear because the intrusive boundaries were covered by talus for many years. These boundaries could, however, be observed from 2014 to 2017. The olivine-norite bodies might constitute syn-plutonic dykes in the biotite granodiorite. It mainly consists of orthopyroxene, plagioclase, olivine, amphibole, phlogopite, and clinopyroxene, in order of abundance. They include small amount of chromite, magnetite, titanite, pyrrhotite, pentlandite, and chalcopyrite. Serpentinite and chlorite occur around mafic minerals. The rocks are modally classified as olivine-melanorite to olivine-melagabbronorite. Geochemically, these rocks have negatively sloped chondrite-normalized REE patterns. The Sr and Nd isotope ratios are enriched relative to typical MORB.