A multi-disciplinary approach to marine shallow geohazard assessment

Seismic velocities together with sediment/rock compaction models are of common use in the oil industry to predict reservoir pressures and to detect and identify any potential hazard associated with over-pressured formations. Excess pore pressure is a key parameter for geohazard assessment, nevertheless this approach is very seldom applied to shallow offshore engineering as it requires expensive ground-truth boreholes. The simultaneous availability in the Bourcart-Herault canyon intertluve (Gulf of Lion - NW Mediterranean) of 1) geotechnical and sedimentological data (300 m boreholes) from the PROMESS project; 2) in situ pore pressure measurements; and 3) High Resolution (FIR) seismic geophysical data showing the presence of active structures in relation to fluid circulation, allows the importance of a multi-disciplinary approach to shallow geohazard assessment to be illustrated through a case study. The velocity field obtained from HR seismic data is interpreted in light of the neighbouring boreholes and resulting velocity anomalies are translated in terms of fluid overpressure and free gas content. Additional in situ surface geotechnical measurements (piezometers) are then taken into account and the role of these parameters is discussed.