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Reference : UMR5275-ERWPAT-001
Workplace : GRENOBLE
Date of publication : Friday, May 15, 2020
Scientific Responsible name : Erwan Pathier
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Title: Present-day deformation of the Apennines (Italy) from InSAR and GPS observations and its implications on the earthquake cycle.
This PhD project is part of a wider scientific project called “EQ-TIME” aiming at quantifying the temporal and spatial slip variability in the earthquake cycle spanning months to million years timescales. The Apennines range, in Italy, is the target area of this project because it is a good example of active mountain belt whose deformation is well documented at different time scales.
The thesis subject focus on the present-day deformation of the Apennines range with the objective to extract the tectonic signal at high spatial resolution from geodetic measurements (GPS and InSAR), in order to learn more about the earthquake cycle variability inside a complex faults system.
The Apennines range is undergoing NE-SW extension at a rate of 3-4 mm/yr [d'Agostino 2014]. The extension is accommodated by 10-30-km long normal faults, arranged in several parallel segmented fault systems located along the ridge belt. The belt has been host to many destructive earthquakes over the last two millennia. This was sadly illustrated by the Irpinia earthquake in 1980 (Mw=6.8), that is the strongest instrumentally recorded earthquake in Italy, and more recently by l'Aquila Mw6.3 earthquake in 2009, or the Amatrice – Norcia seismic sequence in 2016.
The long-wavelength regional deformation signal is already well resolved by GPS. Here, the objective is to better resolve the strain accumulation on individual active faults, the lateral segmentation and to detect possible transient deformations.
The main challenges are to achieve a high spatial resolution (< few hundred meters) and to separate the tectonic signal from other sources of signal presents in the geodetic measurement, that can interact with each other. For instance, recently, the analysis of GPS time series has revealed interactions between hydrological and tectonic forcing (d'Agostino et al. 2018), showing that hydrological and tectonic loading-release processes seems to be closely imbricated.
To deconvolve the seismic cycle from the hydrological forcing, we will perform a systematic high-resolution and time-dependent surface strain mapping in the Apennines. This will ultimately allow to better target potentially loaded faults.
To achieve a high spatial resolution, we plan to perform InSAR time series using Sentinel-1 data (freely available). These data will be processed with the NSBAS chain developed at ISTerre (Doin et al. 2011). The InSAR time series will then be analyzed jointly with GPS times series available in the frame of EPOS project (Plate Observing Plate System, https://www.epos-ip.org/) that are generated in INGV and UGA, that will be complemented with additional data from ITALPOS/SMARTNET network, to derive time-dependent strain maps. To individualize the different contributions in the signal, several methods will be investigated, like Independent Component Analyses (Maubant et al. 2020) or pattern matching technique. Eventually the tectonic signal will be modelled in order to derive the present slip rate and loading parameter on major faults. Stress transfer analyses, including transient signals, will be performed to understand the clustering of earthquakes in the Apennines in interaction with other scientists of the EQ-Time project working at longer time-scales.
Some of the things you will do during this PhD project:
To give a more precise view of the PhD work, here are some expected research activities of the successful candidate:
• Run the NSBAS (Doin et al 2011) processing chain on High Performance Computing cluster under Linux environment to get time-series of InSAR measurement starting from the SENTINEL-1 satellite archives (about 300 acquisitions dates from 2014-2020)
• Adapt the NSBAS processing flow and parameters to the needs of the study, by modifying or creating Python program or Bash scripts.
• Develop program in Python to check the quality of intermediate and final results of the INSAR processing.
• Apply and improve existing algorithms to separate atmospheric signal from deformation signal in InSAR time-series. This could be atmospheric correction from the HRES-ECMWF atmospheric model or from GPS estimate of tropospheric delay (ZTD), or using Independent Component Analysis (ICA) method to improve source separation (Maubant et al 2020).
• Combine InSAR results with already processed GPS time-series to put them in a common Reference frame and better estimate uncertainties level of InSAR measurements.
• Compute velocity map and strain map of deformation
• Integrate all the results in a GIS to be able to combine them with other information like geology or hydrology.
• Looking for spatial heterogeneity in velocity or strain or transient signal in relation to geological information (faults, lithology), hydrological or anthropogenic signals and interpret the tectonics signal in the framework of the earthquake cycle.
• Model the interseismic signal by integrating constraints from geology.
• Do bibliographic research; produce figures (graph, map) to communicate your results inside the project. Write the results of your research in the form of articles, and present those results at international conferences.
Candidates should hold a Master degree in Earth Sciences or equivalent.
A significant part of the thesis work will use numerical computing through programming, signal processing (image processing, time series analysis) modelling and inversion, consequently the candidate should demonstrate some skills and/or interest related to those fields.
Any of the following points are welcome (but not mandatory): programming skills in Python or Fortran ; experience in GPS or InSAR processing ; experience on GIS ; strong background in space geodesy, remote-sensing, active tectonics or earthquake hazards.
Good knowledge of the written and spoken English language is also expected.
Scientific context and working environment
This PhD project is part of the EQ-TIME projet. This project funded by ANR (French Resarch National Agency) start in August 2020 for 4 years. It aims at quantifying the temporal and spatial slip variability in the earthquake cycle spanning months to million years timescales. The project leaded by Lucilla Benedetti from CEREGE, involves four French partners : CEREGE, ISTerre, IRSN and Geosciences Montpellier and collaboration with Italian colleagues.
The starting point of the project is that understanding how successive earthquakes accrue on faults to produce tectonic landforms is still poorly understood. The way deformation is accommodated throughout the crust, in response to the far-field plate tectonics force imposes at plate boundaries, strongly affects the seismic cycle and may control earthquake triggering and the spatial pattern of fault ruptures. The Apennines range, host of the 2016 seismic sequence (5 shocks Mw5-6.5 over 9 months), is a unique area where the accumulation and release of slip over multiple seismic cycles, over time scales of 1yr-1 Myr and spatial scales of 1m-100km, can be determined. The main goal of the project is to combine frontier methodologies in geochronology, remote sensing, geodesy, geophysics, high-resolution topographical data acquisition, seismic hazard modelling, all developed and/or mastered by our teams, to quantitatively constrain how portions of the seismic cycle scale up over multiple cycles to produce the cumulative escarpments we see in the landscape.
The PhD subject “Present-day deformations across the Apennines (Italy) from InSAR and GPS observations and its implications on earthquake cycle” will bring crucial contributions to the EQTIME project, expected outputs of the PhD work, like the InSAR-GPS strain map across Apennines derived from INSAR and GPS are needed for other part of the project.
The PhD student will be hosted at ISTerre at Univ. Grenoble Alpes. He/she will be part of the “Seismic Cycle and Transient Deformation” team. He/she will also join the EQTIME project including partner from CEREGE, IRSN and Geosciences Montpellier and he/she will collaborate with Nicola d'Agostino from INGV (Italy)
Univ. Grenoble Alpes is one of the major multidisciplinary French universities with 55000 students and 100 research laboratories. With 9000 foreign students, half of the PhD students coming from all over the world, and more than 8000 researchers visiting every year, UGA is an internationally engaged and research-intensive university. In 2019 UGA features in the top 100 universities in major international rankings for some of its scientific field, like in Earth Sciences (Shanghai: 21st, NTU: 24, QS: Top 51-100).
A personalized Welcome Center for international students, PhDs and researchers facilitates your arrival and installation (ISSO: International Students & Scholars Office affiliated to EURAXESS)
Surrounded by mountains, the campus benefits from a natural environment and a high quality of life and work environment. For many years, Grenoble has been ranked among the 5 best cities in France where it feels good to study.
ISTerre (https://www.isterre.fr/?lang=en), the institute of Earth Sciences at UGA, is one of the major lab in Earth Science in France with about 300 persons in 9 research teams hosting about 75 PhDs (with a large part of international students) and 8 ERC projects. The team “Earthquake cycle and transient deformation” that is one of the largest group in France of geodesy and remote sensing applied to the study of active faults and earthquakes. The team have a remarkable gender parity among students and permanent staff. Team meetings are mostly done in English. At ISTerre, the successful candidate will have access to dedicated HPC computing facilites for processing large InSAR data sets and for data visualization and analysis. The data needed for the project are either freely available (like SENTINEL-1, atmospheric model), or available through projects where the advisors are involved (Like EPOS) or through collaboration (INGV).
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