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Reference : UMR7516-JERVAN-001
Workplace : STRASBOURG
Date of publication : Thursday, January 09, 2020
Scientific Responsible name : Jérôme van der Woerd
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 February 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
On 10th May 2018, 50 km east of Mayotte, the seismic sequence initiated with a few earthquakes well felt by the population and minor damages. The sequence is exceptional for the region given the high seismicity rate (several dozens of earthquakes every day), the occurrence of numerous chocs above magnitude 5.0 and its duration as it continues until now (September 2019). This seismic activity offshore the island of Mayotte came as a surprise and is a matter of worry in the absence of a good knowledge of the seismic hazard in the region. The displacements recorded by 6 GNSS stations on the island indicates the existence of a deflation zone located at 30 km depth with a volume loss of several cubic-kilometers. The recent seismic recordings on- and off-shore, the in-situ observations (several oceanic cruses including OBS deployments) have revealed the formation of a new volcanic edifice on the oceanic floor and confirmed several seismic swarms.
The goal of the project is to study the seismic sequence in the frame of the seismo-volcano-tectonic context of the region. The island of Mayotte belongs to the Comoros archipelago that crosses the Mozambique channel linking Africa to Madagascar. These volcanic islands rest on a 3700 m-deep oceanic floor and formed in relation to the East African Rift southward propagation since Miocene. The space-time evolution of the seismic sequence needs to be studied in detail to understand the active volcanic and/or tectonic structures to be able to better assess seismic, volcanic and tsunamic hazards of the Mayotte region.
The seismic data available are those from the seismic network onshore Mayotte added to regional stations (Madagascar, east Africa) and for the recent period (March-July 2019) from ocean bottom seismometers deployed around the seismic active zones.
The first step will be devoted to construct a comprehensive homogenous catalog of seismicity before and during the sequence. Due to the high number of recorded earthquakes automatic detection and localization methods will be applied. Source characterization will be improved with relocations techniques. The objective will be to reconstruct the space-time evolution of the sequence (both laterally and vertically) and to highlight possible links with local or regional volcanic or tectonic structures. These local data and teleseismic data will be used to image crustal and deeper structures using seismic tomography.
This project is part of the follow up of the seismic sequence monitored by the French government (MTES ministry) and Centre National de la Recherche Scientifique. Funding agencies are MTES and Bureau de la Recherche Géologique et Minière (BRGM). The PhD will be hired at University of Strasbourg in the Earth and Environmental Science Doctoral School. Advisors are distributed amonbg the 3 involved institutions Institut de Physique du Globe de Strasbourg (IPGS), BRGM, and Institut de Physique du Globe de Paris.
Constraints and risks
The results will be compared to existing oceanic data acquired during the recent and planned cruses but also to geodetic data acquired in Mayotte and Glorieuse islands, which are necessary to constrain the characteristic of deep deformation sources, and to regional geodetic data used to understand regional kinematics. This work will be done simultaneously with other PhDs working on low frequency seismo-volcanic tremors, on regional kinematics, on volcanism and on crustal and lithospheric structures. The results will lead to a better understanding of the current ongoing sequence and of the regional seismic hazard.
Applicants need to send curriculum, motivation letter and letters of support. Additional documents such as Master degree, academic transcript needed.
Applications will be examined by the co-advisors from the 3 involved research institutions (IPGS, BRGM and IPGP). Applicants may be invited for further discussion.
Some experience with seismic data and/or geodetic data processing. Ability to work in groups, interact with other research teams and PhDs.
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