Koki Aizawa 교수

The imaging of hydrothermal systems within volcanoes is critical in evaluating the nature and likelihood of future volcanic activity and hazard assessment. In this study, we present a conceptual model of the hydrothermal system in a volcanic edifice, as deduced from the relationship between electric self‐potential (SP) and high‐resolution resistivity structures. In order to develop a comprehensive model of water flow in volcanoes, we conducted the audiofrequency (10,000–0.3 Hz) magnetotelluric s

Abstract Broadband magnetotelluric (MT) measurements were conducted in 2010 and 2011 in the vicinity of Shinmoe‐dake Volcano in the Kirishima volcano group, Japan, where sub‐Plinian eruptions took place 3 times during 26–27 January 2011. By combining the new observations with previous MT data, it is found that an anomalous phase in excess of 90° is commonly observed in the northern sector of the Kirishima volcano group. Because the anomalous phase is not explained by 1‐D or 2‐D structure with is

The lightning generated by explosive volcanic eruptions is of interest not only as a promising technique for monitoring volcanic activity, but also for its broader implications and possible role in the origin of life on Earth, and its impact on the atmosphere and biosphere of the planet. However, at present the genetic mechanisms and physical properties of volcanic lightning remain poorly understood, as compared to our understanding of thundercloud lightning. Here, we present joint magnetotellur

SUMMARY Magnetotelluric (MT) observations have revealed subvertical electrical conductors that extend from shallow depths into the mid-crust at various geothermal zones, active volcanoes and active faults worldwide. These deeply rooted subvertical conductors have typically been interpreted to represent entire zones of dedicated fluid transport through the crust. We estimate the high-resolution 3-D crustal resistivity structure below the Kuju Volcanoes, Japan, using dense observations from 153 br

Among the microbial phototrophs, those belonging to the cyanobacteria utilize CO2 and HCO−3 for photosynthesis. Some Chlorophyceae mainly take up CO2 in photosynthesis, and others, which have carbonic anhydrase (CA) on their cell surface can utilize HCO−3 as well as CO2. Kinetic studies revealed that most of the HCO−3 is utilized after this ion is converted to CO2 via CA located on the cell surface. Therefore, the actual molecular species which crosses the plasmalemma is mostly free CO2. There i

Mt. Fuji is located in a tectonically unique area, but various aspects of the structure have not been fully explained. Here we show the results from a magnetotelluric survey across Mt. Fuji along a 70 km observation line. The profile shows that a conductive body is located between two resistive bodies at depths greater than 15 km. Low frequency earthquakes occur above the conductor. We interpret these results in a model where beneath Mt. Fuji, the subducting Philippine Sea Plate is split into tw

The M JMA 7.3 Kumamoto earthquake that occurred at 1:25 JST on April 16, 2016, not only triggered aftershocks in the vicinity of the epicenter, but also triggered earthquakes that were 50–100 km away from the epicenter of the main shock. The active seismicity can be divided into three regions: (1) the vicinity of the main faults, (2) the northern region of Aso volcano (50 km northeast of the mainshock epicenter), and (3) the regions around three volcanoes, Yufu, Tsurumi, and Garan (100 km northe

Abstract Phreatic and phreatomagmatic eruptions represent some of the greatest hazards occurring on volcanoes. They result from complex interactions at a depth between rock, water, and magmatic fluids. Understanding and assessing such processes remain a challenging task, notably because a large‐scale characterization of volcanic edifices is often lacking. Here we focused on Miyakejima Island, an inhabited 8‐km‐wide stratovolcano with regular phreatomagmatic activity. We imaged its plumbing syste

From streaming potential measurements, we deduced the zeta potential of 73 volcanic rock samples collected in 11 volcanoes where self‐potential (SP) surveys had also been conducted. Experiments with crushed rock samples and 0.001 mol/L NaCl solution showed a large variation in streaming potential coefficient, which ranged from −2860 to 2280 mV/MPa (deduced zeta potential ranged from −45.1 to 37.2 mV). Among the 73 samples, 9 samples showed positive values, and 11 samples showed small absolute va

Abstract Crustal earthquake ruptures tend to initiate near fluid-rich zones. However, it is relatively unknown whether fluid-rich zones can further promote or arrest these ruptures. We image the electrical resistivity structure around the focal area of the 2016 Kumamoto earthquake sequence by using 200 sites broadband magnetotelluric data, and discuss its quantitative relationship to earthquake initiation, growth, and arrest processes. The ruptures that initiated along the outer edge of the low-