Research
Distributed measurement of seismic and acoustic waves - Distributed Acoustic Sensing (DAS) - on telecom fiber optic cables.
The use of DAS fiber optic data for seismology and environmental science opens up new perspectives for observing areas that were previously extremely difficult to instrument. At Géoazur, we have developed a unique expertise in the acquisition, processing and analysis of this type of data.
This first work, carried out in close collaboration with Anthony Sladen, paved the way for new lines of research and new collaborations. Since 2019, I have been leading work on two topics (1) the generation of in-situ microseismic noise and its link with local meteorological conditions and (2) the detection and the monitoring of boats on underwater DAS data.
Distributed sensing of earthquakes and ocean-solid Earth interactions on seafloor telecom cables
Originality: For the first time, we showed that telecommunications cables can be used to detect the propagation of seismic waves at the bottom of the oceans. The DAS measurement was carried out on the MEUST-Numerenv cable, 41 km long and laid on the bottom from the Toulon coast to the abyssal plain at a depth of 2500m.
DAS system turns the FO cable into 6000 equivalent seismic sensors placed every 6m on the 41 km of the cable and with a sampling frequency equal to 2kHz.
Results: These observations validate a new metrological approach making it possible to measure densely and over large distances various phenomena such as earthquakes (magnitude 1.9 earthquake, however located more than 100km from the cable), the interaction of the swell with the seabed close to the coast, and the generation of microseismic noise on the abyssal plain.
Sladen, Rivet et al. Nature Communication
Supervision : PhD projet of Daniel Mata and Gauthier Guerin
Preliminary assessment of shipping noise monitoring using Distributed Acoustic Sensing on optical fiber telecom cable
We detection and the monitoring noise radiated from boats on underwater DAS data up to the abyssal plain (collaboration with Thales DMS - Rivet et al. in revisition to JASA.
Supervision : Phd project Lucas Papotto
Other related works can be found in publications
Monitoring seismic velocity changes over time, proxy of deformation: from controlled environment experiment to subduction zone.
The driving force behind earthquake triggering, whether it is an aseismic deformation or a fluid pressure disturbance, is generally poorly constrained in seismogenic zones. The objective of my research is to better detect and understand the asismic deformation of the Earth's crust using seismic waves. Two axes are developed (1) an experimental approach on hydrologically reactivated faults to identify the mechanical conditions prevailing around the fault at the time of rupture and (2) a follow-up of the speed variations on active objects (post-seismic deformation at the level of a subduction, active volcanoes and karst.
Experience in a control environment - the experimental approach
Originality: This work combines two approaches: 1) original experiments to activate decametric faults in a controlled environment; 2) a state-of-the-art imaging method for tracking seismic wave velocities that testify to seismic deformation at depth.
Results: During fluid injection experiments, I found that seismic velocity disturbances increased dramatically above 1.5 MPa injection pressure. That corresponds to an increase in the injected flow associated with an asismic dilating shear of the fault as shown by numerical modeling. The actual variations in stress and can be an effective measure for monitoring seismic deformations during fluid injection.
Other related works can be found in publications
High-resolution imaging of crustal structures on a regional scale
Imaging the earth's crust through the measurement of the seismic waves velocity provides information on the nature of the rocks and the crust structure. This image bring knowledge on the depth extension of structures visible at the surface (e.g. sedimentary basin, mountain range) and helps us to better understand regional geodynamics. Another important application concerns seismic hazard. A velocity model close to the true nature of the crust leads to a better localization of earthquakes, and contributes to identify active faults.
Here recent examples :
Southern Alps and the Ligurian Margin Amphibious Tomography
Originality: For the first time we have realized a seismic tomography using an amphibious seismic network.
Results: A high-resolution S-wave image over the entire Ligurian region down to a depth of ten kilometers.
Supervision: This work was obtained as part of the first year master's internship of my student Gauthier Guerin.
Corinthe rift
Originality: First seismic noise correlation study in the Corinth region and S waves.velocity model.
Results: The study highlights the presence of a zone of lower speeds in the southern part of the rift with an elongation in the WNW - ESE direction. This low velocity could be related to the current active tectonic regime and the possible implication of the fluid circulation in a strongly fractured upper crust
Supervision: This work obtained during a research stay at Géoazur of a thesis student at the University of Patras Dimitrios Giannopoulos.
Other related works can be found in publications