題目：損傷制御型コンクリート系構造の実現を目指して

要旨：

これまで，地震災害時の人命保護はもとより，建築物の骨組，非構造材，継続使用性などを保護できる損傷制御型コンクリート系構造の実現を目指して研究を実施してきた。制振ダンパーをコンクリート系構造物に合理的に活用して，地震時の応答低減，靭性能向上，損傷抑制を実現するため，コンクリート系部材との接合部，制振ダンパーを取り付けたコンクリート系構造の部材・部分架構・全体架構の構造実験と数値解析を行い，その力学挙動把握と構造性能評価について研究を行ってきた。近年では，鉄筋とコンクリートの付着を除去することで部材の損傷を制御する技術や，既存建築物の耐震補強工法の開発，柱梁接合部の新たな損傷制御技術の開発なども実施している。また，ドローンを用いた建築物の損傷評価，災害調査に関する先端的な研究も行っている。さらに，国内外で起こった大規模地震の際には現地調査を実施し，調査結果の分析や，被災した建築物の再現解析なども行っている。本セミナーでは，これまでに行ってきた研究活動と，今後予定している研究活動について紹介したい。

Title: An Ocean-Bottom View of Mantle Convection Beneath the Pacific Basin

 

Abstract:

The Pacific basin provides an outstanding natural laboratory for studying a wide range of tectonic and upper-mantle dynamic processes: seafloor spreading, hotspots and other midplate melting and volcanism, multiscale thermal convection, and subduction dynamics, to name just a few.  Historically, direct geophysical constraints on these processes were limited to low-resolution, long-wavelength imaging due to the restriction of most geophysical instrumentation on the surrounding continents and isolated islands.  Over the last decade, advances in seafloor instrumentation (both seismic and electromagnetic) has enabled innovative high-resolution, localized investigation of many of these processes under the umbrella of the grassroots international collaboration PacificArray.  Here I introduce new emerging results from the US ORCA (OBS Research on Convecting Asthenosphere) project, consisting of two year-long seismic arrays in the central and south Pacific.  ORCA was designed to image upper-mantle seismic wavespeeds in two regions where satellite-derived gravity variations display long, linear structures suggestive of small-scale convection in the upper mantle.  At the first site, we find linear blobs of fast and slow material in the mantle beneath the oceanic plate, parallel to the gravity features. These represent cold sinking and warmer rising material, revealing a highly dynamic convective system underneath the plate.  By combining these results with constraints on absolute shear velocity and seismic anisotropy in the two ORCA regions and previous analyses from across the Pacific, we are gaining an improved understanding of the processes controlling the formation, modification, and evolution of the ocean plates and the underlying convection system.

Title: Mapping subduction-induced mantle flows

Abstract:
Laboratory experiments and geodynamic flow simulations demonstrate that poloidal- and toroidal-mode mantle flows develop around subduction zones, driven by the downdip motion and rollback of subducting slabs. To date, inferring deep mantle flow circulation patterns in actual subduction environments using shear wave splitting or surface wave tomography remains elusive, due to limited depth or lateral resolution of these techniques. In this study, we use a new 3-D azimuthal anisotropy model constrained by full waveform inversion to infer deep subduction-induced mantle flows underneath the Middle American and Cascadian subduction zones. At depths shallower than 150~km, poloidal-mode mantle flow is observed perpendicular to the trajectory of the Middle American and Cascadian Trenches. From 300 to 450~km depth, return flows surround the lateral edges of the descending Rivera, Atlantic and Gorda slabs. Furthermore, at 700~km, the study region is dominated by the Farallon anomaly, with fast axis directions perpendicular to its strike, suggesting the development of latticepreferred orientations by substantial strains. These observations provide depthdependent constraints on seismic anisotropy for future mantle flow simulations, and call for further investigations about the deformation mechanisms and elasticity of minerals in the transition zone and uppermost lower mantle.

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　記

　　　　日　　時：　令和4年9月16日(金)　午後１時３０分～　
　　　　開催方法：　インターネット　WEB会議

1. 13:30-13:45
   演題：Classification of Low Frequency Earthquakes at Mount Fuji
   著者：○Adele DOUCET (IPGP/ERI：インターンシップ研修生)・Yosuke AOKI、Nobuaki FUJI (IPGP)
   要旨：We show the first approach of classification of Low frequency earthquakes at Mount Fuji.
2. 13:45-14:00
   演題：三陸沖海底光ケーブルを用いた音響分散型センシングによる地震観測【2021年度所長裁量経費報告】
   著者：○篠原雅尚・山田知朗・悪原 岳・望月公廣・酒井慎一
3. 14:00-14:15
   演題：地震研さくらサイエンス2022の活動概要
   著者：○木下正高・照原陽子・山田祐子・杉崎伊利也・福井 萌

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〒113－0032　東京都文京区弥生1－1－1　
東京大学地震研究所 共同利用担当
E-mail：k-kyodoriyo(at)eri.u-tokyo.ac.jp

※次回の談話会は令和4年10月21日(金)　午後１時３０分～です。

Title: Seismo-acoustic observations of the remarkable atmospheric waves from the January 2022 Hunga, Tonga volcanic eruption

Abstract:  The 15 January 2022 volcanic eruption of Hunga, Tonga produced atmospheric waves that stunned both scientists and the general public. These waves were observed globally by a multitude of instruments and technologies. The most notable atmospheric wave was an acoustic-gravity “Lamb” wave that was detected globally on barometers, infrasound sensors, seismometers, and satellites. This Lamb wave propagated across the globe numerous times and contributed to fast-arriving, hazardous tsunamis that were not forecasted. The Hunga Lamb wave resembled the Lamb wave produced by the 1883 Krakatau eruption, but was observed by a much denser instrument network. Notably, infrasound waves also propagated around the globe numerous times, and audible acoustic waves were heard out to an unprecedented 9000 km. Current wave propagation models do not sufficiently explain these observations. Here I present some notable observations of the atmospheric waves from the Hunga eruption, many of them detailed in a recent highly collaborative manuscript. I focus on the Lamb, infrasound, and acoustic wave observations, including some surprising observations made near the source as well as across the dense geophysical network in Alaska. The atmospheric waves from this eruption provide a landmark dataset for scientists to study for many years.