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(9 January).

************** うなぎセミナーのご案内 (Unagi-seminar) **************

科目：地震学ゼミナールIV（修士・博士）
日時：1月9日（木）14:00～
場所：宇治キャンパス本館E棟2階E-232D
　　　（地震予知研究センター本館セミナー室）

Date and time: Jan. 9, 14:00 ~
Room: E-232D @ Main building
Map: http://www.uji.kyoto-u.ac.jp/campus/map.html

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[発表者1 (Presenter1)]
Plata Martinez Raymundo Omar​​​

[題目 (title)]
First detection of shallow slow earthquakes at the Guerrero Gap, Mexico

[要旨 (Abstract)]
Inan effort to improve our comprehension of the seismic cycle governing the Guerrero gap and the seismic hazard it implies, in November 2017, an array of seven Ocean Bottom Seismometers (OBS) was deployed at the coast of Guerrero, inside the Guerrero gap. Incontrast to the downdip portion of the plate interface, until now, no slow earthquakes activity has been observed updip close to the trench. However, the newly deployed OBS equipment can provide us firsthand observations to search for slow earthquakes activityin the shallow portion of the subducting plate interface. A modifiedcorrelation method was applied in search of shallow tectonic tremors near the trench. After removing possible T-phase and false detections, we detected over 100 tremors located near the trench with depth around 10 km. Their seismic signals do not have a cleararrival of P or S waves, additionally, they are deficient at frequencies above 10 Hz attenuating rapidly but, are efficient at a frequency band between 2 and 8 Hz. Tremors do not show any migration, however, they show a recurrence period of approximately 1 to 3 months. They are grouped in space in four main clusters with characteristic source parameters each. We are now exploring other seismic and geodeticdata, such as GPS and high-resolution bathymetry, to try and explain the tremor observations. Further analysis is still required to understand the nature of these seismic events and the role they play in the complex seismic cycle of the Guerrero gap.​

[発表者2 (Presenter2)]
Atikul Haque Farzi

[題目 (title)]
Ambient noise H/V spectra from OBS around the Japan Trench

[要旨 (Abstract)]
This study attempts to compute H/V spectra by Nakamura (1989) method using ambient seismic noise from ocean bottom seismometer (OBS) data, installed as array of array (AoA) in the Japan Trench area. We look forward to obtain lower frequency H/V peaks to characterizedeep structure like plate interface of the overriding continental Eurasian Plate adjacent to the trench area. Primarily, single station approach has been followed to retrieve H/V spectra for each station. In order to attain the present goal, preprocessingto the data, i.e., instrumental response removal, downsamplig with lowpass filtering, trend and mean removal, and tapering, was applied sequentially. Prior to that, waveforms were plotted to check data quality, especially as our interest is in quite period.Additionally, hourly plots of continuous record was also examined and quiet hours were selected. Then, Fourier amplitude spectra for each component, two horizontal and one vertical, was derived. After that, smoothing was applied to the amplitude spectra usingKonno and Ohmachi (1998) method. Finally, hourly H/V spectral ratio was calibrated by merging two horizontal spectra taking quadratic mean. The future works include automated removal of unwanted arrivals, averaging of hourly plots and day plots for every stationand examining spatial and temporal stability of H/V spectra from OBS. The ultimate goal is to make inversion of the cross-correlated H/V spectra for obtaining shear wave velocity profile under each station so that low velocity zones could be identified forstudying slow earthquake zones on the overriding continental plate.

今後の発表スケジュールは下記の通りです。​

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今後の予定​​
1月16日：栗原（M1），野田（M1）​​
1月23日：森（M1），岡田（M1）​​