Magnetotelluric and temperature monitoring after the 2011 sub-Plinian eruptions of Shinmoe-dake volcano

Three sub-Plinian eruptions took place on 26–27 January 2011 at Shinmoe-dake volcano in the Kirishima volcanic group, Japan. During this event, GPS and tiltmeters detected syn-eruptive ground subsidence approximately 7 km to the WNW of the volcano. Starting in March 2011, we conducted broad-band magnetotelluric (MT) measurements at a site located 5 km NNW of the volcano, beneath which the Shinmoe-dake magma plumbing system may exist. In addition, temperature monitoring of fumaroles and hot-springs near the MT site was initiated in July 2011. Our MT data record changes in apparent resistivity of approximately ±5%, along with a ±1◦ phase change in the off-diagonal component of the impedance tensor (Zxy and Zyx ). Using 1-D inversion, we infer that these slight changes in resistivity took place at relatively shallow depths of only a few hundred meters, at the transition between a near-surface resistive layer and an underlying conductive layer. Resistivity changes observed since March 2012 are correlated with the observed temperature increases around the MT monitoring site. These observations suggest the existence beneath the MT site of pathways which enable volatile escape

Three-dimensional resistivity structure and magma plumbing system of the Kirishima Volcanoes as inferred from broadband magnetotelluric data

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 isotropic resistivity media, 3-D inversions were performed. By applying small errors to the anomalous phase, we successfully estimated a 3-D resistivity structure that explains not only the normal data but also the anomalous phase data. The final model shows a vertical conductor that is located between a deep-seated conductive body (at a depth greater than 10km) and a shallow conductive layer. By applying the findings of geophysical and petrological studies of the 2011 sub-Plinian eruptions, we infer that the subvertical conductor represents a zone of hydrothermal aqueous fluids at temperatures over 400°C, in which a magma pathway (interconnected melt) is partially and occasionally formed before magmatic eruptions. To the north of the deep conductor, earthquake swarms occurred from 1968 to 1969, suggesting that these earthquakes were caused by volcanic fluids

Self-potential studies in volcanic areas(5) : Rishiri, Kusatsu-Shirane, and White Island

We performed self-potential (SP) profiling or mapping in three volcanic fields, Rishiri (northern Hokkaido), Kusatsu-Shirane (central Honshu) and White Island (northern New Zealand). The SP profile on the western flank of Rishiri volcano showed a remarkable high in the summit side, which is similar to many other active volcanoes. Assuming a negative ζ-potential, it is likely that Rishiri volcano has a large hydrothermal circulation system, and therefore still has enough thermal energy to maintain this circulation. Kusatsu-Shirane volcano inversely showed a decreasing trend toward the summit. It is a contradictive result to the previous knowledge that a volcano with remarkable hydrothermal system shows negative SP on the top. We suspect that the low pH of ground water in this area makes ζ-potential null or positive, resulting in the reversed surface SP profile to ordinary cases. This idea should be examined by laboratory experiments in the future. In the Main Crater of White Island volcano, we found some small-scale anomalous patches associated with fumaroles and steaming ground. The small variability of SP is probably attributed to the very low resistivity of the ground. 1

Increase of soluble FcgRIIIa derived from natural killer cells and macrophages in plasma from patients with rheumatoid arthritis

FcgRIII (CD16), one of the low affinity IgG Fc receptors, is found in 2 alternative forms, a transmembrane FcgRIIIa expressed on natural killer (NK) cells and macrophages, and a glycosylphosphatidylinositol-linked FcgRIIIb present on neutrophils. Both FcgRIII are released from the cell surface by proteolytic cleavage and these soluble forms (sFcgRIII) are present in plasma. Since NK cells and macrophages will be activated locally, leading to shedding of FcgRIIIa and its subsequent release into blood, we investigated whether sFcgRIIIa plasma concentrations would be a good marker for disease activity in patients with rheumatoid arthritis (RA). We measured sFcgRIIIa with an immuno-PCR in plasma of NA(1+,2-) phenotyped donors. In this assay, we used CD16 GRM1, which recognizes NA2-FcgRIIIb and FcgRIIIa. We also analyzed precipitated sFcgRIIIa derived from plasma with immunoblotting with CD16 CLB-LM6.30. The concentration of sFcgRIIIa in patients with RA was about 3 times higher than in healthy controls. In controls, the sFcgRIIIa levels in plasma correlated with the number of NK cells in peripheral blood. In RA patients, sFcgRIIIa levels were increased directly proportionally to the concentrations of IgG, IgA, or IgM and to erythrocyte sedimentation rate or Lansbury Index. The electrophoretic mobility of plasma sFcgRIIIa corresponded with sFcgRIIIa derived from NK cells and/or macrophages. In general, plasma sFcgRIIIa originated from both cell types; however, the ratio of sFcgRIIIaNK to sFcgRIIIaMf varied in the RA patients. Increased sFcgRIIIa levels in RA patients were found to be caused by NK cell and/or macrophage activation. Plasma sFcgRIIIa levels may serve as a marker for disease activity in R

紀伊半島におけるNetworkMT法データの時系列解析

令和4年度 Conductivity Anomaly研究会日時：令和4年12月26日（月）09:25-18:30, 12月27日（火）09:00-16:30場所：京都大学防災研究所連携研究棟3階301号室およびZoomThe Kii Peninsula is a geoscientifically interesting region because of the existence of high temperature hot springs, the Kumano caldera, and the Deep Low-frequency Tremors (DLTs). Therefore, the subsurface structure of the Kii Peninsula has been investigated by various disciplines. Among them, electromagnetic method is useful for understanding the spatial distribution of temperature, water and melt beneath the surface. New Energy and Industrial Technology Development Organization (1994), Fuji-ta et al. (1997), Umeda et al. (2003) and Kinoshita et al. (2018) studied the subsurface resistivity structure of the Kii Peninsula with the aid of conventional MT method. Besides these EM studies, Yamaguchi et al. (2009) performed the Network-MT survey in the region almost covering whole Kii Peninsula to elucidate the regional and deep structure. The Network-MT method is superior to the conventional MT method in that it enables us to obtain voltage differences with high S/N ratio especially for the longer period and is relatively free from static effects owing to the long baseline. However, they analysed 2-D resistivity structure by using only a part of the Network- MT data only on one survey line. Three-dimensional analysis is inevitably necessary to investigate the regional and deep structure because coastline distribution as well as bathymetry distribution around the Kii Peninsula not 2-D at all and, in addition, strikes of the igneous intrusion represented by the Kumano acidic rocks are not always consistent with the subduction direction of the Philippine Sea Plate. Therefore, we aim to analyse all the available Network-MT data in the Kii Peninsula. This presentation described the progress report and the results from the time-series analysis. In addition, we discussed about future work of this study.紀伊半島は、高温の温泉、熊野カルデラ、深部低周波地震（DLT）などが存在し、地質学的に興味深い地域である。したがって、紀伊半島の地下構造については様々な方法で調査が行われてきた。その中でも、特に電磁気学的手法は、地表下の温度、水、融解物の空間分布を把握するのに有効である。新エネルギー・産業技術総合開発機構（1994）、Fuji-ta et al. (1997)、Umeda et al. (2003)、Kinoshita et al. (2018)は、従来のMT法を用いて紀伊半島の地下比抵抗構造を調査している。これらの地球電磁気学的研究の他に，Yamaguchi et al. (2009)は，紀伊半島のほぼ全域を対象としたNetwork-MT 法探査を行い，地域構造・深部構造の解明を行った．Network-MT法は、従来のMT法に比べ、特に長周期で高い S/N 比で電位差を測定することができ、また、長い基線により表面近傍の比抵抗コントラストによる歪みの影響を比較的受けにくいという点で優れている。しかし、先行研究では、全データの一部にあたる1測線上のデータのみを使用し、2次元の比抵抗構造を推定している。紀伊半島は複雑な海岸線に囲まれ、海陸分布や周囲の海底地形も到底2次元的では無い。また、熊野酸性岩を代表とする火成岩の走向がフィリピン海プレートの沈み込み方向と必ずしも一致しないため、地域構造や深部構造を調べるには3次元解析が不可決である。そこで本研究では、紀伊半島においてNetwork-MT法によって取得された全てのデータの解析を目指す。本発表では、その進捗状況や時系列解析の結果について報告した。また、本研究の今後の取り組みに関する議論を行った