Oceanographic research has demonstrated that long term time series of critical oceanographic parameters are needed to understand the various ocean systems. ASSEM is the first application of a new concept of sea bed observatory dedicated to the long term monitoring of a small area (some km²), lying on a network of interconnected measurement nodes. It is a project enhancing some marine technologies allowing real time monitoring of the sea bed. The main component of the system is the Communication and Storage Front End, COSTOF. It is an electronic unit providing a set of sensors with the means to communicate with the external world through an underwater network, and to locally store the produced data. The evaluation of this new concept will be carried out through two experiments addressing two seabed problems: slope instability risks and seismic risks. During the Ormen Lange pilot experiment, sensors required for monitoring critical failure surfaces within a slide area, particularly pore pressure sensors, will be installed in boreholes. In other respects, the interest of the ASSEM concept for monitoring a tectonically active area (tectonic movement, creeping, fluid flow) will be demonstrated by a pilot experiment in the Gulf of Corinth.