Thesis examination of Pierre Morena

Pierre Morena will defend his thesis on Tuesday 29 September 2020 at 2.30 pm at the European Institute for Marine Studies (IUEM), amphitheatre "A", Technopôle Brest-Iroise, Plouzané. Due to sanitary constraints, about 100 people will be able to be present in the amphitheatre. His subject :

Paleoseismology and seismic potential of the Lesser Antilles Subduction Zone from sedimentary records.

A summary of his thesis is given below:

The Sombrero-Barbuda segment (Northern Lesser Antilles Subduction Zone) presents a gap in recent seismicity. In order to better estimate the seismic hazard, not well constrained by instrumental or historic seismicity, a marine paleoseismology study based on co-seismic marine deposits has been initiated based on geophysical data (bathymetry, backscatter, HR and VHR seismic) and nine sediment cores collected during ANTITHESIS and CASEIS cruises.

The resulting morpho-sedimentary map shows that sediment cores are supplied by numerous sources principally located on the carbonate platforms (gullies-canyons systems) and on insular slopes (confined canyons). The multi-proxy study of sediment deposits defines numerous sediment gravity flow facies often grouped into thick deposit sequences and/or megabeds (ex: amalgamated turbidites, HmTu complexes).

The chronostratigraphic model defines 81 events identified in between one up to seven piston cores. These events result from numerous and simultaneous slope destabilizations of different independent sources indicating an origin from seismic triggering. The seven best constrained events (especially by the correlation of megabeds in numerous sediment cores) could have had magnitudes as high as 8 or 9. Two alternate recurrence rates are identified from these events: 9420 +/- 600 years and 13630 +/- 1300 years. Some events also correlate with events from the Antigua-Guadeloupe segment and highlight mega-events with an alternate recurrence of ~12 000 years and ~23 600 years.