Submarine expression of the earthquake cycle: morphotectonics analysis of the normal Roseau fault (Lesser Antilles, France) from high resolution bathymetry and 3D photogrammetric models to reconstruct its slip history
Abstract
The 40 km long normal Roseau Fault was responsible for the Mw6.3 2004 earthquake that damaged Les Saintes and generated a 3m run-up tsunami. In 2013, the Odemar cruise recognized the 2004 coseismic rupture, at one site along the scarp base. Markers of the 9-year old submarine rupture were exceptionally preserved in this submarine environment. A second survey (Subsaintes, 2017) was performed to acquire high resolution (1m) multibeam bathymetry data over the cumulative scarp, and systematic video surveys along the scarp base. Videos were used to build 3D models of outcrops using photogrammetry and map the 2004 rupture (Escartin et al., #409647, AGU 2018).
These data allow investigating the rupture history and fault scarp evolution of the fault, by studying different markers witnessing fault activity over different timescales. Here we present its morphological analysis. In some of the 3D models, several slip ribbons exist up to 2-3 m above the 2004 one. Similar to the 2004 ribbon, they are topped by few-cm large horizontal sediment bands, indurated on the scarp, or marked by scarp color changes. We also perform rugosity analysis of different outcrops, up to 20m high, that reveal different levels with changing rugosity, overall increasing upward, indicating longer exposure to sea water. These rugosity bands can be interpreted as past slip surfaces induced by individual earthquakes or clusters. The 200m high cumulative scarp is made of prominent vertical faces, the lower one being the most recent slip surface. It is incised by steep gullies initiated at drainage basins that feed dejection cones at the foot of the scarp. Detailed morphological analysis will allow investigating links between tectonic and submarine surface processes (deposition, erosion as gravitational fall, scarp retreat …) to understand the fault scarp evolution. Future datings and sedimentation rate data will allow to quantify and reconstruct the slip history of the Roseau Fault, and associated seismic risk.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S41D0579B
- Keywords:
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- 4314 Mathematical and computer modeling;
- NATURAL HAZARDSDE: 7215 Earthquake source observations;
- SEISMOLOGYDE: 7221 Paleoseismology;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS