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(June, 8).

************** 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：2023年 6月 8日 (木) 13:15~
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)
今回のみ、連携研究棟301で開催です。以下の地図の77番の建物です。
https://www.kyoto-u.ac.jp/ja/access/campus/map6r-uji

Date and Time: 2023-06-08, 13:15~
Place: Room No. #301, Collaborative Research Hub, DPRI, Uji Campus or Zoom (Hybrid)
This Thursday seminar will be held in Room #301, Collaborative Research
Hub, DPRI, Building 77 on the map;
https://www.kyoto-u.ac.jp/en/access/uji-campus

　　　　Please join the seminar on-site, especially students who need credit.

Speaker: Atikul Haque Farazi

Title: Imaging the accretionary prism of the Indo-Burmese subduction system in the Bengal Basin by joint inversion of the HVSR and group velocity dispersion curve of ambient seismic noise

Abstract:
　The world’s largest and thickest (15–22 km) sedimentary Bengal Basin(BB) in Bangladesh hosts the north-south trending blind megathrust of the active Indo-Burmese subduction system between the Indian and the Burmese plates. Nearly ~12–24 mm/yr of convergent strain is being accumulated within the continually shortened, deformed and uplifted accretionary prism of the subduction system, which makes this densely populated region highly vulnerable to an unappreciated seismic hazard. But this region is still seismically less studied. While the decollement plane of the subduction system is very shallow, ~5–9 km, and the deformation front is still blind and believed to be somewhere in the center of the BB, none of the previous tomographic images provide enough resolution within the upper ~20 km of the basin.
　This study uses the ambient noise data of 10 seismic sensors within the BB, which were not utilized in the previous tomographic studies, for having the tomographic image of the central BB with higher resolution and reveal the ongoing subduction related structure with more detail information. The sparsely recorded seismic data from the year of 2011 to 2015 were cross correlated between the vertical components of the station pairs for Rayleigh wave group velocity estimation, between 6–33 s period, with certain quality control measures to the raw data and the finally stacked cross correlated waveforms (CCFs). Thus, a total of 37 group velocity dispersion curves (DCs) were obtained from the CCFs. Then, 2-dimensinal (2D) group velocity maps were obtained for each period using the Fast Marching Method for Surface Wave Tomography. Because of lacking enough ray density for the periods >20 s, the analysis was further carried between 6–20 s. Then DC curves were extracted from the 2D maps for several spatial points. The horizontal-to-vertical spectral ratio (HVSR) was computed (from 0.05 to 1 Hz) from ambient noise data for ~15 days. The joint inversion was performed for a 1-dimensional (1D) profile for the point where both the DC and the HVSR were available and then the model was propagated for the nearby points. The joint analysis helped mitigating the non-uniqueness of the inversion. The 1D profiles were then interpolated for a subsurface 2D S-wave velocity model along an east-west transection of the study area and up to ~8–17 km depth. The primary result is very promising because it has higher resolution, agrees well with the previous tomographic results and the current hypothesis about the structure and the ongoing tectonic process within the Indo-Burmese subduction related accretionary prism. This study could be complementary to the previous models derived from group velocity dispersion curves. Such study could also benefit the industries for exploration.