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(Dec 17).

************** うなぎセミナーのご案内 (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：2020年12月17日（木）14:00～
場所：オンライン(Zoom)

Date and time：Dec 17 (Thursday), 14:00～
Site：Online by Zoom

====

[発表者1 (Presenter1)]
Admore Mpuang

[題目 (title)]
Seismic structure beneath Botswana: considering dipping and anisotropic structures

[要旨 (Abstract)]
In receiver function analysis, velocity models developed under the assumption of horizontal isotropic interfaces suffer inaccuracies in the presence of dipping and anisotropic structures. In such cases, the receiver functions exhibit back-azimuthal variation of amplitude and delay time. Such features of receiver functions have been observed in records from stations located in the Okavango rift zone and Limpopo belt in Botswana. In this study, the presence of dipping and anisotropic structures at shallow crustal to mantle depths is considered in redefining the seismic structure beneath the different tectonic regions in Botswana. As a first step, high frequency (3Hz) receiver functions are subjected to harmonic decomposition to constrain the presence of dipping and anisotropic structures in the shallow crust. The harmonic stacks indicate the presence of shallow dipping interfaces in the Limpopo and Kheis mobile belts, possibly between the overlying metasediments and crystalline metamorphic basement. Inversion for Vs, dip and anisotropy magnitude and orientation will be performed using an adaptation of the genetic algorithm inversion method to be developed in this study. The results of this study will provide insights on the deformation history of the southern African lithosphere as well as current geotectonic processes.

[発表者2 (Presenter2)]
Pousali Mukherjee

[題目 (title)]
Structural control of slow slip in the Chile Subduction zone: estimates from Receiver Function method

[要旨 (Abstract)]
The Chile region in South America is one of the most active tectonic regions where the Nazca plate subducts beneath the South American plate. In addition to megathrust earthquakes, the region has also been reported to host slow slip earthquakes from shallow subsurface to deeper portions. Investigating the lithosphere of the slow earthquake area versus non slow-earthquake area in Chile subduction zone is crucial in understanding the role of the internal structure to control slow slip. In this study, we are using teleseismic receiver function method to estimate the lithospheric parameters in northern and central Chile using 28 broadband stations in an around the slow slip region. The results show difference in parameters in mantle wedge and subducted oceanic crust, indicating that mantle wedge and subducted oceanic crust have a key role to play in occurrence of slow slip in the Chile subduction region.

====