記のとおり地震研究所談話会を開催いたします。

対面での開催を再開しておりますので、地震研究所へお越しいただければ幸いです。

なお、お知らせするZoom URLの二次配布はご遠慮ください。また、著作権の問題が

ありますので、配信される映像・音声の録画、録音を固く禁じます。

 　　　　　　　　　　　　　 　　記

　　　　　　　　　日　　時：　令和8年2月20日(金)　午後1時30分～

　　　　　　　　　場　　所：　地震研究所1号館2階　セミナー室

　　　　　　　　　　　　　　　Zoom Webinarにて同時配信　

1. 13:30-13:45

演題：三浦半島断層群・相模トラフ調査観測プロジェクト部【所長裁量経費報告】

著者：○石山達也・三宅弘恵・蔵下英司・古村孝志・酒井慎一、宍倉正展(産業技術総合研究所)

要旨：三浦半島断層群・相模トラフ調査観測プロジェクト部の研究成果について、「三浦半島断層帯（主部／武山断層帯）における重点的な調査観測」の成果概要とともに報告する。

2. 13:45-14:00

演題：Seismic Source Characterization in the Marmara Sea Using Distributed Acoustic Sensing

著者：○Ji ZHANG･Aitaro KATO、 Ahmet Anil DINDAR(MARTEST Research and Training Center, Gebze Technical University) and Wei WANG(Key Laboratory of Earth and Planetary Physics, Institute of Geology, Geophysics, Chinese Academy of Sciences/College of Earth and Planetary Sciences, University of Chinese Academy of Sciences)

3. 14:00-14:15

演題：Revealing Widespread Non-Double-Couple Earthquakes in Tottori, Japan

著者：○Ji ZHANG･Aitaro KATO、Wei WANG(Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences/College of Earth and Planetary Sciences, University of Chinese Academy of Sciences)、 Shin’ichi SAKAI、 Satoshi MATSUMOTO(Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University)、Yoshihiro ITO(Disaster Prevention Research Institute, Kyoto University)

4. 14:15-14:30

演題：スロー地震の断層滑りの広がりを規定する地下構造【成果発表補助 成果報告】

著者：○悪原　岳、白石和也（JAMSTEC）、辻　建（東大工）、山下裕亮（宮崎公立大）、杉岡裕子（神戸大）、Atikul Haque FARAZI(バリシャル大)、大柳修慧・伊藤喜宏（京都大）、新井隆太・荒木英一郎・藤江　剛・中村恭之・利根川貴志（JAMSTEC）、東　龍介・日野亮太（東北大）、望月公廣・武村俊介・山田知朗・篠原雅尚

5. 14:30-14:45

演題：新燃岳2008年噴火の以前、噴火直前及び以後に発生した火山性地震の深度分布とb値の特徴

著者：○及川　純、田島靖久（日本工営(株)中央研究所）

○発表者

※時間は質問時間を含みます。

※既に継続参加をお申し出いただいている方は、当日Zoom URLを自動送信いたします。

※談話会のお知らせが不要な方は下記までご連絡ください。

〒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8年3月23日(月)　午後１時30分～です。

Title:

Rheological modeling to assess the effects of seamount subduction

 

Abstract:
The Kyushu–Palau Ridge (KPR) acts as a structural boundary, separating two distinct subduction zones: the Ryukyu Trench, where the old West Philippine Basin (WPB) is subducting, from the Nankai Trough, where the younger Shikoku Basin of the Philippine Sea Plate descends. This contrast is reflected in a sharp thermal gradient, with high heat flow toward the Shikoku Basin and markedly lower values toward the WPB. Notably, the lowest heat flow occurs seaward of the subducting KPR, a region that also exhibits tectonic tremors and low-frequency earthquakes. It has been hypothesized that these correlated features result from stress and strain modulation caused by seamount subduction. To test this hypothesis, we conducted two-dimensional numerical simulations with realistic rheology for the Hyuga-Nada region. Our aim was to evaluate how seamount subduction affects the overlying plate and its potential links to both slow earthquake conditions and the observed heat-flow anomalies. We developed four numerical models to analyze the sensitivity of the system to seamount subduction as a function of the incoming plate’s age: an old plate (47 Myr) without (Model 1) and with (Model 2) a seamount, and a young plate (25 Myr) without (Model 3) and with (Model 4) a seamount. Forearc sediments were assigned a depth-dependent density, ranging from approximately 1600 kg/m³ to 2600 kg/m³ based on data from a nearby IODP site, assuming an exponential increase with depth. These sediments exhibit strain-weakening behavior, with an initial internal friction angle of 10° and cohesion of 1 × 10⁶ Pa, decreasing to 5° and 1 × 10⁵ Pa after deformation. In contrast, the oceanic and continental crust maintain constant values (30° and 1 × 10⁶ Pa, respectively). The modeling results indicate that seamount subduction enhances forearc deformation for both old and young plates, manifested as shear bands in the upper crust. The spatial distribution and intensity of these shear bands reflect the combined influence of plate age and the presence of a seamount. Models without a seamount (1 and 3) display nearly constant deviatoric horizontal stress and systematic shear-band development, indicative of strong interplate mechanical coupling. Conversely, models that include a seamount (2 and 4) show significant stress variations controlled by the seamount’s position, which locally suppress forearc fracturing within a specific depth interval. This suppression coincides with the seamount entering high-density sediments. Prior to this stage, interaction with low-density sediments generates permanent deformation at relatively low stress. After the seamount passage weakens the sediments, shear-band development resumes and subduction dynamics regain dominance. Plate age further modulates this response: Model 2 (old plate) produces greater forearc deformation and higher strain rates than Model 4 (young plate).

1. Title: Exploring the Universe with Neutrinos: From IceCube to IceCube-gen2

 

Abstract:
Neutrinos offer a unique window into some of the most energetic and distant phenomena in the universe. The IceCube Neutrino Observatory at the South Pole is currently the world’s largest neutrino detector, utilizing a cubic kilometer of Antarctic ice instrumented with thousands of optical sensors to detect Cherenkov radiation from neutrino interactions. In this colloquium, I will introduce the science behind IceCube, explain how neutrino detection and reconstruction work in ice, and highlight key discoveries — including the identification of astrophysical neutrino sources and constraints on fundamental particle physics. I will also share insights and experiences from my recent expedition to the South Pole, contributing to the IceCube Upgrade project to enhance the observatory’s low-energy sensitivity and calibration capabilities. Finally, I will present an outlook on IceCube-Gen2, the next-generation neutrino observatory, aiming to significantly expand IceCube’s scientific reach and open new frontiers in astroparticle physics.

 

2. Title: Recent advances in data-driven modeling of cosmic ray and atmospheric lepton fluxes

 

Abstract:
Accurate models of the cosmic ray spectrum and the fluxes of atmospheric muons and neutrinos provide essential inputs for interpreting astrophysical neutrino observations, neutrino oscillation studies, and investigating hadronic interaction models, as well as a wide range of applied fields, including muon tomography. In this talk, I will present our recent progress toward a fully data-driven and muon-calibrated description of atmospheric lepton fluxes. The daemonflux framework combines “foundation models” of the cosmic ray spectrum, numerical cascade calculations (MCEq), and hadronic interaction models with a global calibration procedure using muon flux and charge ratio measurements. I will highlight the latest update of the Global Spline Fit (GSF2025), a flexible cosmic ray flux parameterization covering energies from the GeV scale up to 100 EeV, and discuss how daemonflux predictions compare with underground muon measurements using the MUTE framework and demonstrate how these results enhance the description of recent KM3NeT muon data, achieving excellent agreement with observations and paving the way for precision atmospheric flux predictions.