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Crustal deformation is analyzed assuming an elastic medium in most cases. However, inelastic deformation plays an important role in various crustal processes such as tectonic stress accumulation and long-term topographic formation. We have been trying to isolate inelastic deformation signals from geodetic observation data. The M9.0 2011 Tohoku earthquake has brought a unique opportunity in this regard. The postseismic deformation pattern was reversed from the interseismic one. However, along the concentrated contraction zone along the Japan Sea coast, we identified persistent localized contraction before and after the Tohoku earthquake, which is considered to be an inelastic contribution. The identified inelastic strain rate is consistent with the geologically estimated value, indicating a contribution of inelastic processes to long-term deformation. Associated with the Tohoku earthquake, crustal deformation of the Japan island arc has been time-dependent. Since the strain components change in time satisfying the stress equilibrium, time-dependent strain rate data allows us to estimate the heterogeneous distribution of elastic properties and inelastic contribution. Also, we can assume that the observed strain can be considered a sum of elastic and inelastic strains. By assuming the plane stress condition, elastic deformation of the crust can be predicted with an appropriate boundary condition. Then the residuals can be considered inelastic contributions. We will present an overview of these approaches and their applications to GNSS data in Japan to demonstrate how the exploration works, together with their tectonic implications.&nbsp, The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Institute for Space-Earth Environmental Research, Nagoya University, held a regional contribution program of “Letʼs study earthquake and active fault around Nagoya city” for the higher grade elementary school students on July 31–August 1, 2019. The twenty-five students took part in the program. The first day they went to Ogaki and Motosu, Gifu by bus and visited the Kinsho-zan Kaseki-kan (Museum) to observe the Permian fossils, Neo River to collect Shikamaia fossils, and the Seismic Faults Observation & Experience House to observe Neodani Fault, which ruptured causing the Nobi earthquake in 1891. We successfully made a meaningful field program. The second day began with a lecture on mechanism of earthquake occurrence and fault slipping by Prof. Sagiya. After the lecture, the students studied about natural disasters and their mitigation at the Disaster Mitigation Research Building (Gensai-kan), and took part in a hands-on experiment of making fault by the use of flour and cocoa powder. In the afternoon, they discussed about what was learned during this experiential learning program and summarized it in posters. Finally, they made poster presentation by groups. The program ended a success. The post-program questionnaire shows that the participants enjoyed the program a lot and learned many new things., 名古屋大学宇宙地球環境研究所は、2019年7月31日（水）と8月1日（木）の2日間にわたり、小学校4年生から6年生25名を対象とした夏休み体験学習を実施した。初日は、大型バスをチャーターして、子ども達25名とスタッフ11名、総勢36名で、岐阜県大垣市、本巣市に出向いた。金生山化石館では、高木洋一元館長から化石についての説明を受けた後、古生代の化石であるフズリナやシカマイア（巨大二枚貝）の観察を行った。根尾川河原では、根尾公民館の三本木隆館長のご指導のもと、シカマイア化石の採集を行った。また、根尾谷地震断層観察館・体験館では、1891年の濃尾地震によって形成された根尾谷断層の観察を行い、濃尾地震の揺れを実体験した。2日目は、名古屋大学減災館で、減災連携研究センターの鷺谷威教授から地震発生や断層形成のメカニズム、地震防災について学んだ。その後、研究所共同館Ⅱに移動し、小麦粉とココアを用いた断層形成実験を行った。最後に、体験学習で学んだことを班ごとに話し合ってポスターにまとめ、発表会を行なった。

We investigate the evolution of tectonic background stress and elastic as well as inelastic strain in a crust‐upper mantle system around an infinitely long vertical strike‐slip fault in a self‐consistent mechanical earthquake cycle model. In the early stage of the stress evolution, deformation of the crust and the upper mantle is dominated by a uniform simple shear. Shear localization in the lower crust starts when coseismic rupture extends to the entire brittle upper crust. Together with this transition, the earthquake recurrence intervals decrease by an order of magnitude due to a basal drag originated from a localized plastic flow of the lower crust. After the shear zone is fully developed in the lower crust, the fault slip rate catches up with the far‐field velocity and earthquakes starts to occur periodically. Such a steady state can be reached in several hundred thousand years from the beginning, which includes few hundreds of earthquake cycles. A shear zone with large cumulative strain needs a few million years to develop under an intraplate strike‐slip fault, which is much longer than the time for shear strain rate to be localized. The model successfully reproduced evolution of tectonic stress around an intraplate strike‐slip fault, interacting with the development of localized shear zone in the lower crust. The model demonstrates the importance of considering the whole mechanical system in which rheological structure and fault activities interacting with each other for the better understanding of the intraplate earthquakes., ファイル公開：2019-04-01