更新日:2024.07.18
Updated: 2024.07.18
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, 18).
************** 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:2024年 7月 18日 (木) 13:30~
場所:京都大学 防災研究所 本館E-232D
Date and Time:2024-07-18, 13:30~
Place:Uji Campus Main Building E232D
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Speaker(発表者)1: Naoyuki Abiru
Title(題目):
時系列スタッキングを使用した琉球海溝でのSSE検出の試み
Abstract(要旨):
スロー地震とは,通常の地震より断層がゆっくりとすべる現象であり,世界各地で発生していることが知られている(例えば,Obara & Kato.,2016).スロー地震の中でも,測地学的な周期帯域にシグナルを持つものはSlow Slip Event(以下:SSE)と呼ばれている.琉球海溝沿いでは多数のSSEの発生が知られるが,その分布は,八重山諸島や沖縄本島南東沖,喜界島沖などに集中しており,それ以外のところではあまり発生していない(Nishimura, 2014).沖縄本島の周辺では,南部では多くのSSEが検出されているのに対し,北部では,あまり検出されていないが,北部ではGNSS観測点が少なくないため,本当にSSEの発生頻度に差があるのか,よくわかっていなかった.
2019年に沖縄本島北部にもGNSS観測点が京都大学により設置され,観測網の問題は解決された.そこで,本研究では,新たなGNSSデータを用いて,沖縄本島周辺などの琉球海溝中南部のSSEの発生分布とその履歴を明らかにし,SSEの発生分布の地域性の原因の解明を目指す.その第一歩として,Bletery and Nocquet(2023)により提案されたスタッキング手法を用いて,SSEに伴う地殻変動の確認を行なった.沖縄本島周辺とSSEの規模が大きい八重山諸島においてスタッキング処理を行なった結果,八重山諸島では,先行研究で報告されているSSEに伴う地殻変動を確認した.
* * * * * * * * * * * * * *
Speaker(発表者)2: Kai Koyama
Title(題目):
Global investigation of foreshock acceleration prior to large earthquakes
Abstract(要旨):
Research on precursors of large earthquakes is crucial for discussing the predictability of earthquakes. Particularly, foreshock activity occurring before large earthquakes has been actively studied. Bouchon et al. (2013) claimed that foreshock activity increased acceleratively just before many large earthquakes at plate boundaries around the Pacific Rim. Additionally, Nishikawa & Ide (2018) reported that foreshock activity increased acceleratively in the few days before the 2008 Ibaraki-oki earthquake. Furthermore, simulations and laboratory rock experiments also suggest that foreshock activity increases acceleratively just before an earthquake (e.g., McLaskey, 2019). However, Bouchon et al. (2013) have been criticized for not adequately considering the effects of earthquake clustering (Felzer et al., 2015). Additionally, the analysis by Nishikawa & Ide (2018) is limited to seismic activity off the coast of Ibaraki, and it is unclear whether similar acceleration phenomena can be confirmed for large earthquakes worldwide. Therefore, this study globally investigates foreshock activity before large earthquakes using the ETAS model (Ogata, 1988), a worldwide standard statistical model of seismic activity. In this study, based on the results of simulations and rock experiments, we added a new term representing the acceleration of foreshock activity into the ETAS model. By applying this new ETAS model to seismic activity before large earthquakes worldwide, we aimed to detect and quantify the characteristics of the acceleration phenomena in foreshocks. Several cases of foreshock activity that can be interpreted as acceleration phenomena were observed before large earthquakes. Some examples of these will be introduced. Furthermore, we plan to compare seismic activity before small earthquakes to verify whether the acceleration phenomenon is unique to large earthquakes and to discuss the randomness of the acceleration phenomenon by comparing it with synthetic earthquake catalogs.
---------- ---------- ---------- ----------
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, 18).
************** 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:2024年 7月 18日 (木) 13:30~
場所:京都大学 防災研究所 本館E-232D
Date and Time:2024-07-18, 13:30~
Place:Uji Campus Main Building E232D
---------- ---------- ---------- ----------
Speaker(発表者)1: Naoyuki Abiru
Title(題目):
時系列スタッキングを使用した琉球海溝でのSSE検出の試み
Abstract(要旨):
スロー地震とは,通常の地震より断層がゆっくりとすべる現象であり,世界各地で発生していることが知られている(例えば,Obara & Kato.,2016).スロー地震の中でも,測地学的な周期帯域にシグナルを持つものはSlow Slip Event(以下:SSE)と呼ばれている.琉球海溝沿いでは多数のSSEの発生が知られるが,その分布は,八重山諸島や沖縄本島南東沖,喜界島沖などに集中しており,それ以外のところではあまり発生していない(Nishimura, 2014).沖縄本島の周辺では,南部では多くのSSEが検出されているのに対し,北部では,あまり検出されていないが,北部ではGNSS観測点が少なくないため,本当にSSEの発生頻度に差があるのか,よくわかっていなかった.
2019年に沖縄本島北部にもGNSS観測点が京都大学により設置され,観測網の問題は解決された.そこで,本研究では,新たなGNSSデータを用いて,沖縄本島周辺などの琉球海溝中南部のSSEの発生分布とその履歴を明らかにし,SSEの発生分布の地域性の原因の解明を目指す.その第一歩として,Bletery and Nocquet(2023)により提案されたスタッキング手法を用いて,SSEに伴う地殻変動の確認を行なった.沖縄本島周辺とSSEの規模が大きい八重山諸島においてスタッキング処理を行なった結果,八重山諸島では,先行研究で報告されているSSEに伴う地殻変動を確認した.
* * * * * * * * * * * * * *
Speaker(発表者)2: Kai Koyama
Title(題目):
Global investigation of foreshock acceleration prior to large earthquakes
Abstract(要旨):
Research on precursors of large earthquakes is crucial for discussing the predictability of earthquakes. Particularly, foreshock activity occurring before large earthquakes has been actively studied. Bouchon et al. (2013) claimed that foreshock activity increased acceleratively just before many large earthquakes at plate boundaries around the Pacific Rim. Additionally, Nishikawa & Ide (2018) reported that foreshock activity increased acceleratively in the few days before the 2008 Ibaraki-oki earthquake. Furthermore, simulations and laboratory rock experiments also suggest that foreshock activity increases acceleratively just before an earthquake (e.g., McLaskey, 2019). However, Bouchon et al. (2013) have been criticized for not adequately considering the effects of earthquake clustering (Felzer et al., 2015). Additionally, the analysis by Nishikawa & Ide (2018) is limited to seismic activity off the coast of Ibaraki, and it is unclear whether similar acceleration phenomena can be confirmed for large earthquakes worldwide. Therefore, this study globally investigates foreshock activity before large earthquakes using the ETAS model (Ogata, 1988), a worldwide standard statistical model of seismic activity. In this study, based on the results of simulations and rock experiments, we added a new term representing the acceleration of foreshock activity into the ETAS model. By applying this new ETAS model to seismic activity before large earthquakes worldwide, we aimed to detect and quantify the characteristics of the acceleration phenomena in foreshocks. Several cases of foreshock activity that can be interpreted as acceleration phenomena were observed before large earthquakes. Some examples of these will be introduced. Furthermore, we plan to compare seismic activity before small earthquakes to verify whether the acceleration phenomenon is unique to large earthquakes and to discuss the randomness of the acceleration phenomenon by comparing it with synthetic earthquake catalogs.
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© Research Center for Earthquake Hazards.
© Research Center for Earthquake Hazards.