2-Main areas of interest

Earthquake Geology, Paleoseismology and Seismic Hazard

Seismicity -recorded by instruments or described through their effects in archives- cover a reduced, or even tight, period of time which is not sufficient to characterize the earthquake potential (in magnitude and in recurrence) of a specific area. This is particularly the case for intraplate areas (IAEA TECDOC 1767, 2015), but also for active ones like California (Schwartz et al., 2014). This is the primary reason why, in seismic hazard analyses, we include geological data that document prehistorical events through their effects on morphology and within sediment recordings.

In my research, I study the active tectonics and earthquake signature in "young" sediments (Quaternary) and/or morphology, in order to figure out the quake parameters from them.

Left: ancient and 2016 earthquake surface ruptures are recorded within alluvial sediments in a trench in Central Italy (trench in 2017);

Right: the succession of earthquakes have left a wonderful scarp in the morphology of the Ecuadorian Andes (Billecocha, Cotacachi region).

One critical issue is to convert the geological information in terms of earthquake strength, i.e. magnitude, so that the information brought by geologists could be transformed in expected ground shaking at a site (Seismic Hazard Analysis, SHA). To achieve this, the common use is to call for "empirical relationships" predicting magnitude from measured fault parameters (surface displacement, surface rupture length). It is also very important to provide datasets for the evaluation of another hazard that can jeopardize facilities and installations: the permanent ground surface dislocation (Fault Displacement Hazard Analysis, FDHA).

As a field geologist, I search for contributing to post-seismic surveys, which are necessary opportunities to increase our experience and understanding of earthquakes, as well as the to merge data for empirical relationships and fault displacement analysis. I participated to several "post'seismic" surveys (5-Post-Earthquake Surveys ).

I also contribute to paleoseismological investigations across the world to improve the knowledge of active faults.

Seismotectonics in intraplate areas where  seismicity is diffuse

One part of my research is focused on intraplate seismotectonic setting. Not all the damaging earthquakes are linked to faults that are known at the ground surface through recent geology (say, Quaternary) evidence. And because this seismicity can be an issue for safety, we have to deal with, face the lack of surface information and find relevant data to characterize the earthquake potential of the so-called diffuse seismicity areas. 

In the late 1990's to early 2000's, the RENAG network of continuous GPS receivers has been set up to measure the horizontal velocity field and estimate the relative displacement of blocks and then, hopefully, estimate the earthquake potential of fault zones or areas of deformation. Almost 20 years after, the community now recognize that this goal is not achieved for most of the potentially actove faults, because of the very low deformation rates in metropolitan France. However, recent geodetical data, including GNSS and InSAR (see below),  revealed compelling evidence of vertical relative displacements and deformation in the Alps, giving interesting highlights on regional geodynamics.

In many intraplate places, we do  not have a clear idea of the current status of the crust (in terms of stress or deformation pattern); only historical or instrumental earthquake catalogs, geological and structural maps... but still sites and populations to protect. A classical method is to develop areal sources, which definition is mainly based on structural geology, large-scale geophysics, spatial distribution of seismicity, focal mechanisms when available, etc... This is a much less exciting challenge for a field geologist, but this is of crucial relevance for seismic hazard assessment for critical (or not) sites.

After the M. Mathey thesis, we have in hands a rich set of geodetical and seismological data to propose a resolved 3D seismotectonic zoning scheme for the Western Alps.