Phone: +33 (0)2 38644606
Fax: +33 (0)2 3864336
email: t.dewez@brgm.fr

Mailing address:
ARN - MAS, BRGM
(French Geological Survey)
3 Av. C. Guillemin
45000 Orleans - France

Thomas Dewez

My research is principally aimed at detecting and measuring how landscapes remember their tectonic history and past earthquakes. The critical assumption behind this research is that understanding how past deformation occurred holds the key to understanding the potential occurrence of future earthquakes. Destructive earthquakes have the worrying habit of occurring on faults that had passed unappreciated before. Screening the landscape for signs of tectonic activity is thus a first step towards mitigating hazards linked to tectonics. For this, I use various techniques ranging from field survey to photogrammetric Digital Elevation Model production and Geographic Information System toolboxes to analyse and represent tectonic deformation.

Here is how landscapes work. When left alone for thousands of years, a landscape evolves because of rain, snow, wind and ice all of which produce erosion, transport and sedimentation of material. In a nutshell, slopes decay, rivers flow and depressions fill in due to climatically controlled variables. When tectonic forces enter in the game, relief is created and tectonically induced landforms start growing. It is this tectonic signature that geomorphologists are looking for; the size and age of these landforms tell us how rapidly tectonics is working. Interactions between tectonic and surface processes becomes rapidly mind-boggling because

1. tectonic forces vary in intensity depending on which region is studied; large forces presumably produce large deformation but only occur along active plate boundaries, as a corollary, smaller forces are at work toward plate interiors;
2. large deformations are easier to detect than small deformations and are more clearly relatable to tectonic causes;
3. to see large deformation, one could wait a long time. But this is without counting with the erasing effect of surface processes.

Ideally, one would want to study the region between rapidly moving tectonic plates in arid conditions. But this is unfortunaly not where the largest populations are to be found.

During my PhD research at Brunel University (West London, UK, 1998-2003), I worked on developing semi-automated techniques to help geomorphologists measure tectonic deformation in coastal settings. These were appied to the Arkitsa region, an area broken by poorly known, though well-identifiable, sets of normal faults located along the southern shore of the Gulf of Evvia, in central Greece. Technical developments were addressing how, with a set of off-the-shelf scanned aerial photographs, one can extract reliable elevation measurements. This led to developing an algorithm to flag and remove automatically spurious elevations. In addition, with the high-resolution Digital Elevation Model, a terrace delimitation algorithm was devised to help mapping these coastal features in a consistent fashion. Finally, with a battery of standard structural geology tools never applied to Digital Elevations Models so far, I examined the pattern of deformation of the coastline. This revealed a new mode of deformation unsuspected by previous research.

During my post-doctoral research at BRGM - the French Geological Survey - (Orleans, France), I was confronted with the geomorphology of European plate interior in the active Rhine Graben and of the Vienna Basin (Austria). My research there, in the framework of the European Project branded ENvironmental TECtonics [ENTEC], addressed how one could detect signs of tectonic activity in the continental landscape. The issue is very tricky because there is a very strong climatic signal, a comparatively weak tectonic signal and hardly any usable landform to infer long term tectonic deformation. Since October 2004, I am a permanent research engineer at BRGM in the Department of Natural Risk and Land Management, where I deal with coastal dynamics, landform monitoring and seismotectonic hazard matters.