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うなぎセミナー 7/2

うなぎセミナー 7/2

セミナー等

SEMINARS

更新日:2020.05.07

Updated: 2020.05.07

  • 開催場所:オンライン(Zoom)
  • Place: オンライン(Zoom)
  • 開催日時:2020年7月2日(木) 14時00分~
  • Date and Time: 2020年7月2日(木) 14時00分~

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 2).

************** うなぎセミナーのご案内 (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:2020年7月2日(木)14:00~
場所:オンライン(Zoom)

Date and time:July 2 (Thursday), 14:00~
Site:Online by Zoom

====

*1)* [発表者 (Presenter)]
Chintan Timsina

[題目 (title)]
One-dimensional reference velocity model in the source region of 2015 Gorkha earthquake, Nepal

[要旨 (Abstract)]
The 2015 Gorkha earthquake (Mw 7.8) in central Nepal provides the opportunity to better understand the fault geometry of Main Himalaya Thrust (MHT) that has hosted series of disastrous earthquakes. Several previous studies on the geometry of MHT and crustal structure in this region share the analogous feature of low angle decollement beneath the lesser Himalaya is connected with the deeper ductile zone beneath the higher Himalaya by ramp structure. However, variations on the dips of the ramp, the dimension of flat portion and presence of another ramp in the shallower portion controlling both along and across-strike rupture propagation are still a subject of huge interest.
Multiple studies on the Gorkha earthquake aftershock sequence have produce catalogs either from local and/or teleseismic arrival time data. All catalogs have similar features like two separate seismic belts located north and south of the main coseismic slip area and narrow to broad along-strike variation of the northern belt, however, depths of the events among these catalogs vary significantly. Yamada et. al., (2019) produced the aftershock catalog by using an automatic onset and hypocenter determination procedure from continuous waveform recorded by 42 temporary seismic stations. In this study, we choose nearly 1500 aftershocks from around 15000 events of that catalog which are detected by more than 20 recording stations. The epicenters of these events cover the entire aftershocks zone and represent sufficient characteristics of the aftershock sequence. We visually and manually inspect all the waveform and repick seismic phases arrivals. In this presentation, we will report an optimum 1D velocity models for both P and S-wave obtained through joint inversion of earthquake hypocenters and velocity variation. We will further discuss the aftershocks characteristic and their association with the structural variation of MHT in the source region of 2015 Gorkha earthquake.


*2)* [発表者 (Presenter)]
Tha Zin Htet Tin

[題目 (title)]
Estimation of Present-Day Relative Plate Motion and Crustal Deformation in Myanmar using GNSS Data

[要旨 (Abstract)]
Relative motion between India, Eurasia, Sunda and Burma plates is responsible for the major geological processes in Myanmar. Due to the subduction - collision between the India-Eurasia and Burma plates, fold and thrust belts are developed in the western part of Myanmar. Another major active geological structure in Myanmar is the 1200km long Sagaing Fault, a right-lateral strike slip fault, north-south trending along central Myanmar.
A GPS network was constructed under the collaboration between Earth Observatory of Singapore (EOS), Myanmar Earthquake Committee (MEC), Department of Meteorology and Hydrology, Myanmar (DMH) and Myanmar Survey Department (MSD) in Myanmar since 2012. Additional campaign measurements have been conducted since 2016 for more coverage of the data at Indo-Myanmar (Burma) Ranges in the west. Data from 17 continuous stations and 44 campaign stations which combined with previous results by Vigny et al., (2003) and Maurin et al., (2010) are used to improve the site positions and velocities in this analysis.
We confirmed that the present-day relative motion and the direction of movement between the GNSS stations are consistent with the dextral strike slip of Sagaing fault at a rate of 14 – 24 mm/yr. The 17 stations on the eastern side of the Sagaing Fault show smaller velocities with respect to the station on the Sunda plate than those on the western side of the Sagaing Fault . It is noteworthy that the western stations still have significant motion with respect to station on the India plate. Deformation in the western Myanmar may reflect primarily the effect of the Rakhine-Bangladesh subduction zone, or a combination of the subduction and internal deformation of the Burma plate. We fit a 2-D dislocation model to the observed displacements around the Sagaing Fault to estimate locking depth of segments. The fitting shows the locking depth is 14.8 – 16 km which deeper along the Southern segments than the Northern segments of Sagaing Fault based on available data.

====

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 2).

************** うなぎセミナーのご案内 (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:2020年7月2日(木)14:00~
場所:オンライン(Zoom)

Date and time:July 2 (Thursday), 14:00~
Site:Online by Zoom

====

*1)* [発表者 (Presenter)]
Chintan Timsina

[題目 (title)]
One-dimensional reference velocity model in the source region of 2015 Gorkha earthquake, Nepal

[要旨 (Abstract)]
The 2015 Gorkha earthquake (Mw 7.8) in central Nepal provides the opportunity to better understand the fault geometry of Main Himalaya Thrust (MHT) that has hosted series of disastrous earthquakes. Several previous studies on the geometry of MHT and crustal structure in this region share the analogous feature of low angle decollement beneath the lesser Himalaya is connected with the deeper ductile zone beneath the higher Himalaya by ramp structure. However, variations on the dips of the ramp, the dimension of flat portion and presence of another ramp in the shallower portion controlling both along and across-strike rupture propagation are still a subject of huge interest.
Multiple studies on the Gorkha earthquake aftershock sequence have produce catalogs either from local and/or teleseismic arrival time data. All catalogs have similar features like two separate seismic belts located north and south of the main coseismic slip area and narrow to broad along-strike variation of the northern belt, however, depths of the events among these catalogs vary significantly. Yamada et. al., (2019) produced the aftershock catalog by using an automatic onset and hypocenter determination procedure from continuous waveform recorded by 42 temporary seismic stations. In this study, we choose nearly 1500 aftershocks from around 15000 events of that catalog which are detected by more than 20 recording stations. The epicenters of these events cover the entire aftershocks zone and represent sufficient characteristics of the aftershock sequence. We visually and manually inspect all the waveform and repick seismic phases arrivals. In this presentation, we will report an optimum 1D velocity models for both P and S-wave obtained through joint inversion of earthquake hypocenters and velocity variation. We will further discuss the aftershocks characteristic and their association with the structural variation of MHT in the source region of 2015 Gorkha earthquake.


*2)* [発表者 (Presenter)]
Tha Zin Htet Tin

[題目 (title)]
Estimation of Present-Day Relative Plate Motion and Crustal Deformation in Myanmar using GNSS Data

[要旨 (Abstract)]
Relative motion between India, Eurasia, Sunda and Burma plates is responsible for the major geological processes in Myanmar. Due to the subduction - collision between the India-Eurasia and Burma plates, fold and thrust belts are developed in the western part of Myanmar. Another major active geological structure in Myanmar is the 1200km long Sagaing Fault, a right-lateral strike slip fault, north-south trending along central Myanmar.
A GPS network was constructed under the collaboration between Earth Observatory of Singapore (EOS), Myanmar Earthquake Committee (MEC), Department of Meteorology and Hydrology, Myanmar (DMH) and Myanmar Survey Department (MSD) in Myanmar since 2012. Additional campaign measurements have been conducted since 2016 for more coverage of the data at Indo-Myanmar (Burma) Ranges in the west. Data from 17 continuous stations and 44 campaign stations which combined with previous results by Vigny et al., (2003) and Maurin et al., (2010) are used to improve the site positions and velocities in this analysis.
We confirmed that the present-day relative motion and the direction of movement between the GNSS stations are consistent with the dextral strike slip of Sagaing fault at a rate of 14 – 24 mm/yr. The 17 stations on the eastern side of the Sagaing Fault show smaller velocities with respect to the station on the Sunda plate than those on the western side of the Sagaing Fault . It is noteworthy that the western stations still have significant motion with respect to station on the India plate. Deformation in the western Myanmar may reflect primarily the effect of the Rakhine-Bangladesh subduction zone, or a combination of the subduction and internal deformation of the Burma plate. We fit a 2-D dislocation model to the observed displacements around the Sagaing Fault to estimate locking depth of segments. The fitting shows the locking depth is 14.8 – 16 km which deeper along the Southern segments than the Northern segments of Sagaing Fault based on available data.

====

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© Research Center for Earthquake Hazards.

© Research Center for Earthquake Hazards.