Recent studies of Fe-K edge XANES (X-ray Absorption Near Edge Structure) spectrometry on Fe³⁺/ΣFe ratio of volcanic glasses are reviewed. Calibration curves relating the pre-edge feature of X-ray absorption spectrum of Fe at ~7111–7116 eV and Fe³⁺/ΣFe ratio of silicate glass are established using synthetic silicate glasses of various compositions, which Fe³⁺/ΣFe ratios are determined chiefly by Mössbauer spectroscopy. The calibration curves enable us non-destructive, high-precision analysis of Fe³⁺/ΣFe ratio of silicate glass with spatial resolution of <10 µm and relatively short measuring time. Fe³⁺/ΣFe ratio determined by the method is largely consistent with those determined by wet chemistry and Mössbauer spectroscopy. The method is applied to volcanic glasses (tiny melt inclusions in phenocryst minerals and quenched groundmass glasses) to quantitatively determine their Fe³⁺/ΣFe ratios. The results are used to investigate the effect of shallow magmatic processes (degassing and crystallization) on fO₂ of magma, the redox states of primitive melts from various tectonic settings (mid-ocean ridge, hotspot (Hawaii), arc and back arc basin) and the relations between the redox state and other geochemical features of the source mantle.

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Historical documents show that the Miho Peninsula was separated from the land by a narrow channel, called the “Seorido no Watashi” (in Japanese: Seorido = local name, no = of, Watashi = passage). This passage may have been formed by partial destruction by tsunami. In the present study, we conducted a geological survey using two sediment cores (10–11 m in length) near the ancient passage in order to investigate the age and formation process of the passage. The cored sediments were mainly composed of sand and gravel deposited on the shore of the peninsula and did not contain any materials available for ¹⁴C dating. These results did not provide any evidence of the process or timing of channel formation.

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Based on the geological research of the Enrei Formation in the Enrei-Tokawa area in the southern part of Median Uplift Belt of the North Fossa Magna region, central Japan, we discuss here the late Early to Middle Pleistocene tectonics in and around this area including the motion on the central part of the left-lateral Itoigawa-Shizuoka Tectonic Line active fault system (ISTL-AFS). The ISTL-AFS runs through the southwestern margin of this area and is situated in the connecting portion between the NNW-SSE ~ N-S trending northern segment in the Matsumoto Basin and the NW-SE trending southeastern segment in the Suwa Basin. The Enrei Formation here has steeply to moderately dipping chaotic structures without distinctive preferred orientations in map-scale, in contrast with the overall near-horizontal structures of this Formation and the coeval Komoro Group outside of the study area. The complicated horizontal shortening to form some folds with gently-plunging axes and irregular block-rotations about vertical axes probably formed this structural architecture. The age and space relationships between the Enrei Formation and the ISTL-AFS suggest that the chaotic structures were formed in association with the left-lateral strike-slip motion on the ISTL-AFS that formed the pull-apart Suwa Basin after 0.8 Ma and before 0.4 Ma. During and after this event, this area uplifted and eroded to form a gentle relief surface. The surface on the western side was then covered by the younger gravels derived from the Chikuma Mountains on the east that have uplifted at the average rate of about 2.5 m/ky. since 0.4 Ma. The activity of N-S ~ NNE-SSW trending high-angled faults, the Gakenoyu-Midoriko Faults, played an important role in this uplift. These sequential events including horizontal shortening, vertical-axis rotations, faultings, and rapid uplifting of the Chikuma Mountains were probably caused under the transpressional regime assosicated with the restraining bend of the left-lateral ISTL-AFS. Marked differences in tectonic landforms on both sides of the Suwa Basin are also responsible for its lateral motion.

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GRACE (Gravity Recovery and Climate Experiment) mission had clarified global time-variable gravity fields since 2002. The time-variable gravity fields represent spatiotemporal mass redistribution on the Earth. Using GRACE level-3 data provided by CNES/GRGS, we attempt to detect signals of mass movement related to volcanic eruptions. We focus on the gravity data for 13 volcanoes where large (VEI 4 or higher) eruptions occurred, and perform a regression analysis with linear, annual, and semiannual components. We find that only Icelandic volcanoes have notable signals of positive changes in the linear trends of gravity (Eyjafjallajökull and Grimsvötn) and negative offset (Eyjafjallajökull) associated with the eruptions. These signals can be attributed to responses of surrounding glacial system to the eruptions rather than mass movement by the eruption themselves. In addition, small but significant signals have also been detected in other volcanoes, but their interpretation is still difficult.

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Slow earthquakes, which consist of low-frequency earthquakes, tremors, and slow slip events (SSEs), have occurred at the Nankai Trough subduction zone in southwestern Japan. Among others, long-term SSEs at deeper parts of the locked zone on the subduction plate interface had been detected by onshore GNSS array. Nowadays, thanks to development of seafloor GNSS-A measurement, we have been able to estimate long-term SSEs at a shallow part of the subduction zone. Here we try to detect slow events along the Nankai Trough, using a Markov Chain Monte Carlo method which does not assume a fixed duration of unsteady displacement. We find six observation points with unsteady displacement, and interpret that four types of slow events with various periods occurred. One point experienced a very long-term (over three years) undefined, probably a landslide-like event. Another point might be influenced by previously-reported very-low-frequency earthquakes. Another point moved due to a SSE found by onshore GNSS array. For the other three points, the unsteady displacement represented a shallow SSE near the trench as proposed by a recent study.

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