下記のとおり地震研究所談話会を開催いたします。

ご登録いただいたアドレスへ、開催当日午前中にURL・PWDをお送りいたします。

なお、お知らせするzoomURL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5年3月17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：情報科学－固体地球科学融合研究プロジェクト部 活動報告 【所長裁量経費成果報告】

著者：○長尾 大道、情報科学－固体地球科学融合研究プロジェクト部メンバー

2. 13:45-14:00

演題：地震波形の全体・局所領域に対する複数の深層学習モデルを統合した地震検出手法

著者：○徳田智磯・長尾大道

要旨：既存の検出手法(GPD)を発展させ、地震波形全体の情報に加え、波形の局所情報をモデルに取り入れることにより、より精度よく地震を検出できる手法を開発した。

3. 14:00-14:15

演題：多方向ミュオグラフィによる伊豆大室山火砕丘の三次元密度トモグラフィ

著者：○宮本成悟、長原翔伍(神戸大学）、森島邦博・中野敏行（名古屋大学）、

小山真人（静岡大学）、鈴木雄介（STORY）、市川雅一

要旨：火砕丘は火山の基本的な形態の一つであり、その詳細な内部構造や形成時のマグマの動きを明らかにすることは、噴火の性質を理解する上でも、火山災害の軽減のためにも重要である。我々は、大室山火砕丘の3次元密度構造を明らかにするために、多方向ミュオグラフィ調査を実施した。火山の周辺11ヶ所に多方向ミュオグラフィに最適化された原子核乾板検出器を設置しました。原子核乾板に記録されたミューオンの飛跡は、高速自動読み出し装置で読み取られた。得られた10方向のミュオグラフィ画像に線形インバージョンを用いることで3次元密度構造を推定した。この観測結果と先行研究による地形・地質学的な制約から、見つかった高密度領域はそれぞれ火砕丘の中央火道、そしてそこから伸びる3方向の放射状ダイクと推察されます。西方向に伸びるダイクは西麓の小さな溶岩流を作り、南方向に伸びるダイクは小さな側面噴火を起こし、小火口を形成したと推察した。Nagahara, Miyamoto, Morishima, Nakano, Koyama, Suzuki, “Three-dimensional density tomography determined from multi-directional muography of the Omuroyama scoria cone, Higashi–Izu monogenetic volcano field, Japan.” Bull Volcanol 84, 94 (2022). https://doi.org/10.1007/s00445-022-01596-y

○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zoomURL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5年4月21日(金)　午後１時３０分～です。

Title: Mayotte’s submarine volcano: seismicity, tomography, and the future seafloor observatory

 

Abstract:

Mayotte’s submarine volcano system was first identified in 2018 when several earthquakes and very-long-period earthquakes were seen on global seismic networks. The volcano’s presence was later confirmed in February 2019 in a sea campaign called MAYOBS, during which a new volcano edifice was discovered ~40 km offshore Mayotte. There was only 2 land stations on Mayotte at the time of the first MAYOBS campaign. We understood so little of Mayotte’s submarine volcano and the crisis that many more MAYOBS sea campaigns were conducted over a period of 4 years. In total, 23 sea campaigns were conducted to deploy/recover ocean-bottom seismometers – an unprecedented number of sea campaigns for an unprecedented submarine volcano eruption. In this talk, I will present a brief summary of seismological studies conducted by myself and the REVOSIMA (Mayotte Seismic and Volcanic Monitoring Network) seismology group: how we detected more 30k events and relocated more than 5,000 of them, the first tomographic image we have of the volcano system, and the future seafloor observatory that will be installed to monitor Mayotte’s submarine volcano in the future.

Title:  Volcano imaging from distributed passive sources.

Abstract
A large portion of the world’s active volcanoes are glaciated, and the significant topographic gradients result in a large amount of distributed gravity and temperature driven icequake activity. These small impulsive events typically excite high frequencies (1-20 Hz), and their pervasive nature makes them ideal for Green’s function reconstructions through seismic interferometry and for statistical analysis using diffusion and radiative transfer arguments. We showcase our progress in developing an eventual “ground up” workflow and code base particularly well-suited to temporary nodal deployments that encompasses detection and databasing of icequakes, Bayesian coda cross-correlation for Green’s function reconstruction, envelope modeling via radiative transfer with concurrent event localization, and array-based scattering imaging for conduit system mapping (with Institut Langevin and UJF Grenoble). We show applications and ongoing work at Erebus volcano, Antarctica.

Title: High-resolution exposure and sensor deployments: Chances for seismology and risk research

 

Abstract:

The substantial reduction of disaster risk and live losses, a major goal of the Sendai Framework by the United Nations Office for Disaster Risk Reduction (UNISDR) requires a clear understanding of the dynamics of the built environment and how it affects, in case of natural disasters, the life of communities, represented by local governments and individuals. Communities that participate in risk assessments increase their understanding of efficient risk mitigation measures. Our Global Dynamic Exposure model and its technical infrastructure build on the involvement of society in a crowd-sourced approach. Simultaneously, it helps educating communities in the risks they are facing and how they can prevent losses of lives.

 

We are in the process of creating super high-resolution data products for better assessment of seismic risk. Based on the plethora of open data and volunteer geographic information like OpenStreetMap, we have created a super high-resolution and dynamic exposure model that attempts to characterize probabilistically every building on Earth for better risk assessments. We are employing a crowd-sourced capturing of exposure indicators using OpenStreetMap (OSM), an ideal foundation with already more than 500 million building footprints (growing by ~150’000 per day), and information about school, hospital, and other critical facilities. With our OpenBuildingMap system, we are harvesting this dataset by processing every building in near-realtime. We are collecting exposure and vulnerability indicators from explicitly provided data (e.g. hospital locations), implicitly provided data (e.g. building shapes and positions), and semantically derived data, i.e. interpretation applying expert knowledge. The expert knowledge is needed to translate the simple building properties as captured by OpenStreetMap users into a probabilistic assessment of vulnerability and exposure indicators and subsequently into probabilistic building classifications as defined in the Building Taxonomy 2.0 developed by the Global Earthquake Model (GEM). With this approach, we increase the resolution of existing exposure models from aggregated exposure information to building-by-building vulnerability.

 

Simultaneously, we have started with dense acceleration-sensor deployments in the wider Tokyo area. We have explored the utility of the smartphone-type sensors built into small devices directly plugged to power outlets in the wall for the use by volunteers and companies. We deployed 10 devices to private people in the Zama region in 2021 and 50 devices in the larger Tokyo region in 2022 for about a half year each. Additionally, we have equipped the 48-story Tokyo Metropolitan government building in Shinjuku, Tokyo, with many devices on floors ranging from 1st to 44^th, and one 6-story building of the Tokyo Narita International Airport with many devices on four floors. All devices have provided us with both three-component acceleration records and seismic intensities in the Japan Meteorological Agency (JMA) scale, which is familiar to non-professional Japanese people. The measured seismic intensities on different floors and within the same floor show a variety of values different to the reported JMA intensity for the wider area. Also, we have obtained human assessments of experienced seismic intensity.

 

We want to present our future plans for massive sensor deployments and their goals. We are planning to expand the experiment to more than 1000 households in the Tokyo area for better defining the needs of homeowners, tenants, or facility managers. Further plans include equipping neighboring buildings with sensors in order to estimate the ground-motion variability on small spatial scales to better understand the necessary measuring bandwidth for ground motions and intensities. A collaboration with ISC will show how the sensor data can be used for improving overall seismic networks in terms of location uncertainty and initial localization speed.

 

 

 

下記のとおり地震研究所談話会を開催いたします。

ご登録いただいたアドレスへ、開催当日午前中にURL・PWDをお送りいたします。
なお、お知らせするzoomURL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5年2月17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：数値モデルとレーダー観測による噴煙柱の3次元再構築 【短期招聘研究員成果報告】

著者：○Magfira SYARIFUDDIN (State Agriculture Polytechnic of Kupang) 、鈴木雄治郎

要旨：We incorporate the velocity estimates from a weather radar observation into a three-dimensional (3D) numerical model to reconstruct the volcanic ash column of a VEI-2 eruption in Sinabung, Indonesia, on 19 February 2018.

2. 13:45-14:00

演題：小型磁気センサーを用いた磁場観測装置の開発状況の報告【所長裁量経費成果報告】

著者：○臼井嘉哉

要旨：小型磁気センサーであるMIセンサーを用いた地磁気観測装置の開発を行っている。本発表では開発の現在の進捗状況を報告する。

3. 14:00-14:15

演題：Detection and analysis of seismoacoustic wavefield of Popocatepetl volcano, Mexico

著者：○Gerardo MENDO-PEREZ、 Alejandra ARCINIEGA-CEBALLOS(UNAM, Mexico)、Robin MATOZA(UCSB, United States) 、Alejandro ROSADO-FUENTES (UNAM, Mexico)

要旨：We present the infrasound and seismic signals associated to the explosive activity of Popocatepetl volcano.

4.14:15-14:30

演題：ブロードバンド・バイブレーター震源を用いた超高分解能反射法地震探査による活断層の構造イメージングの可能性【所長裁量経費成果報告】

著者：○石山達也、中西利典（ふじのくにミュージアム）、加藤直子（日本大学）

要旨：「大規模伏在活断層の構造・活動性解明プロジェクト室」の一環で、駿河トラフ陸上延長部の伏在断層の構造的な特徴と完新世後期〜歴史時代の活動について、ボーリング調査・高分解能反射法地震探査などに基づき検討した結果を報告する。

5.14:30-14:45

演題：「地震記象が少ない時代の『やや大きい地震』総覧充実」プロジェクト室

【所長裁量経費成果報告】

著者：○石瀬素子・酒井慎一・中川茂樹、石辺岳男（地震予知総合研究振興会）、

室谷智子（国立科学博物館）

6.14:45-15:00

演題：2023年トルコ南部の地震：強震動

著者：〇三宅弘恵、山中浩明（東京工業大学）、近藤久雄（産業技術総合研究所）、Ozgur Tuna OZMEN（トルコ災害緊急事態対策庁）、Aysegul ASKAN（中東工科大学）、

Gulum TANIRCAN（ボアジチ大学カンデリ地震観測研究所）

○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zoomURL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5年3月17日(金)　午後１時３０分～です。

Squeezing and lifting – modes of long-term forearc deformation in the Northern Chile subduction zone

Bernd Schurr, GFZ German Research Centre for Geosciences

Subduction zone forearcs deform transiently and permanently due to the frictional coupling with the converging lower plate. Transient stresses are mostly the elastic response to the seismic cycle. Permanent deformation is evidenced by forearc topography, upper plate faulting and earthquakes; its relation to the megathrust seismic cycle is debated. Here we study upper plate seismicity in the northern Chile subduction zone as a proxy for forearc brittle deformation. We find that seismicity is distributed unevenly and a dramatic increase correlates both with a break in the morphology and tectonics of the Coastal Cordillera and the onset of a change in subduction obliqueness. Earthquakes in the South American crust under the sea and under the Coastal Cordillera show a remarkably homogenous north-south, i.e., trench-parallel, compressional stress field. Earthquake fault mechanisms are dominated by trench-perpendicular thrusts. Further inland, where the lower plate becomes uncoupled, the stress field is more varied with direction east-west to southeast-northwest (approx. convergence parallel) dominating. The stress-regime above the plate-coupling-zone, almost perpendicular to plate convergence direction, may be explained by a trench-parallel strain component from a change in subduction obliqueness due to the concave shape of the plate margin, which we demonstrate by investigating inter-plate earthquake slip vectors. From these, we derive a strain rate estimate and compare it to one derived from upper plate earthquakes. In the southern part of our study area, where convergence obliqueness is constant, upper plate seismicity is sparse, but Coastal Cordillera elevation and the uplift rate are higher than in the north. A new relocation of two megathrust earthquake aftershock sequences reveals a flat-ramp-flat structure that we interpret as underplating of a 3 km thick slice of eroded material and/or oceanic crust. This structure is also visible in the residual gravity field and in a tomographic model of the region. Our study demonstrates thus two very different mechanisms of forearc thickening active on two neighboring segments of a subduction zone.