Numerical simulations of earthquake-generated tsunami scenarios in the vicinity of the Guadeloupe archipelago: effect of the Marie-Galante graben on the wave propagation

Guadeloupe archipelago (i.e. Basse-Terre, Grande-Terre, Marie-Galante, Désirade, Les Saintes, Petite-Terre) is located in the northern Lesser Antilles arc. Like the other islands of this sector of the arc Guadeloupe archipelago is exposed to earthquake hazard originating from megathrust earthquakes (e.g. the Mw = 8.5, February, 8, 1843 earthquake, located North-East of Grande-Terre) and shallow depth (~ 10-20 km) normal faults activity (e.g. the Mw = 6.3, November, 21, 2004, Les Saintes earthquake). The 10 km depth, November, 21, 2004, Les Saintes earthquake was located on the Roseau fault, which belong to an en-echelon fault system along the inner volcanic arc. Though of minor impact for the population of the archipelago (i.e. no casualties and small damages), this event revealed the potential hazard of such type of tsunami in the region. In the present study we focus on the propagation of tsunami waves within the Marie-Galante graben (MGB). MGB is a deep structure (~ 2000 m deep) with its highest flanks either emerging or forming a shallow water coral reef plateform (depth < 100 m). Such features are recognized to generate wave breaking and reflexion. Therefore we investigate these effects during the propagation of waves generated from different tsunami scenarios: (i) a 1843 megathrust-type earthquake (Mw = 8.5), located in the same sector as the original; (ii) a 1839 megathrust earthquake-type (Mw = 8) with an epicentre located East of Martinique coast; (iii) and a normal-fault earthquake with an epicentre on a submarine transect of Morne-Piton fault system on the southern flank of MGB. For each scenario we provide results on the source features (i.e. source wavelength, height of water disturbance) but also on the velocity of the waves before they hit the MGB's flank. At last we present results for one scenario of a parametric study on the effect of the angle of incidence with the graben taking into account different positions of the source. Numerical simulations of the each tsunami sources were carried using the Tsunami Open and Progressive Initial Condition System (TOPICS), for the sources, and FUNWAVE 2, for the waves propagation, respectively.