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(November 11).

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

科目：地震学ゼミナールIV B, D / Seminar on Seismology IV B, D（修士・博士）
日時：2021年 11月 11日 (木) 14:00~
場所：京都大学 防災研究所 本館E-232D または オンライン(Zoom)

Date and Time：2021-11-11, 14:00~
Place：Uji Campus Main Building E232D or Zoom (Hybrid)

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Speaker (発表者)：Shukei Ohyanagi

Title (題名)：Seismicity near the trench controlled by the shallow slow earthquake activities?

Abstract (要旨)：
　The Japan Trench subduction zone is a cradile for various types of seismic activities, such as Mw9.0 Tohoku-oki megathrust event, VLFE, or SSE. In past few years, ocean bottom seismic observations by S-net, the cabled network of ocean bottom seismometers (OBSs) and other dense networks of free-fall tyoe OBSs reveal astonishing slow earthquake activities of this subduction zone, which characterized by the along-strike transition from the slow earthquake region to the megathrust earthquake zone [Nishikawa et al., 2019]. However, a spatiotemporal relationship between the slow earthquake activities and the surrounding microseismicities is still unclear due to lack of an earthquake catalog constructed based on the OBSs, not only onshore seismic stations. Here, we created the earthquake catalog for the region surrounding the slow earthquake clusters of offshore Fukushima near the Japan Trench. The catalog is constructed based on the OBS observation performed during 2016 to 2017. During this time period, Ohta et al. (2019) repoted five bursts of shallow tectonic tremor in this region. To investigate standard seismicity during the tremor activity, we applied Earthquake Transformer (EQT) [Mousavi et al., 2020], the deep learning module to perform detection and phase picking of microearthquakes to the OBS dataset. The detected events are located using hypomh [Hirata and Matsu’ura, 1987] with station corrections estimated from PS converted phases [Iwasaki et al., 1991]. Based on the catalog, we find that four out of five tremor burst activities synchronized with the earthquake swarm at the up-dip side of the shallow tectonic tremor region. Also, template matching analysis reveals that at least one of the earthquakes within the swarm is the repeating earthquake. Our study suggests that the seismicity very near the trench is strongly affected by the nearby shallow slow earthquake activities.

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