今週のうなぎセミナーについてお知らせいたします。

Here is information of the Unagi-seminar(July, 21).

************** Seminar on Seismology IV A, C /地震学ゼミナールIV A, C (Unagi Seminar) **************

科目：地震学ゼミナールIV A, C / Seminar on Seismology IV A, C（修士・博士）
日時：2022年 7月 21日 (木) 14:00~
場所：京都大学防災研究所 連携研究棟301号室（大セミナー室）または オンライン(Zoom)

Date and Time：2022-07-21, 14:00~
Place：Seminar Room #301, DPRI Collaborative Research Hub, Uji Campus, Kyoto University or Zoom (Hybrid)

https://www.kyoto-u.ac.jp/ja/access/campus/map6r-uji
（構内マップ中の77番の建物です。）

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Presenter (発表者)：松尾 凌(Ryo MATSUO)

Title (題目)：遠地誘発地震（動的誘発地震）の発生条件の定量化に向けて

Abstract (要旨)：
　地震の遠地誘発（動的誘発）とは、比較的大規模な地震による表面波などが遠隔地で応力を乱して伝播することによって地震を誘発する自然現象のことであり、そのメカニズムは十分に解明されていない。東北沖地震による典型的な即時遠地誘発のケースなど遠地誘発の観測事例や南カリフォルニア地域の事例 (Miyazawa et al. ,2021)を取り上げ、誘発地震の発生場所の特徴や、誘発したもととなる地震の特徴、発生した誘発地震の活動状況の特徴などについて紹介する。本研究では, 遠地誘発を定量化することを目指す。 手始めに、2022/3/16福島県地震前後の日本列島の地震活動の変化を、n値やz値、β値と言った複数の方法で計算し、評価する。

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Presenter (発表者)：森永 優

Title (題目)：データ同化と地震警報システム
　　　　　(the Data Assimilation and Earthquake Warning System)

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Presenter (発表者)：Atikul Haque Farazi

Title (題目)：S-wave velocity profile estimation based on analysis of horizontal to vertical spectral ratio of earthquake coda in offshore Fukushima, NE Japan

Abstract (要旨)：
　Earthquake coda contains information about the subsurface structure due to multi-scattering. We exploit this information and present the S-wave velocity profiles of the sedimentary sequences and the upper crustal layers for three broadband ocean bottom seismometer (OBS) stations in the offshore Fukushima region by the analysis and inversion of earthquake horizontal to vertical spectral ratio (EHVSR). To obtain the EHVSR, the tail of earthquake signals with ?200s length was used. Using a number of earthquake signals, an average EHVSR was obtained for each station in the frequency range between 0.05 and 10 Hz. Compared to HVSR of noise in the study area (Farazi et al. 2022), the results show stable curves below 0.1 Hz. The stability of the EHVSR below 0.1 Hz was further evaluated considering both its azimuthal variation and time evolution. We also investigate the energy equipartition in the coda windows following the method by Shapiro (2000). For the inversion we assume that the wavefield is diffuse, and use the recently developed “hvgeneralized” (Lontsi, 2015, 2019) algorithm that accounts for the effects of the water layer on the HVSR and performs full EHVSR inversion. The results were constrained using prior subsurface information of the study area.
A relative shortcoming of the present approach is the requirement of energetic and long duration coda, which potentially limits the number of observations. Lower frequency range of observation with HVSR was increased successfully in the offshore environment without further treatment to the seismogram. S-wave profiles down to 10000 m depth were derived with improved resolution for the sedimentary sequences and the upper crustal layers. The results are useful for future seismic and geodynamic studies.

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