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P014

ASSEM :Array of Sensors for Long Term SEabed Monitoring of Geohazards

A0026 Roland Person IFREMER Centre de Brest

A0027 D.Strout Norvegian Geotechnical Institute

A0028 Pierre Briole Institute de Physique du Globe-Department de Sismologie UMR 7580

A0029 G. Etiope Institute Nazionale di Geofisica e Vulcanologia

A0033 M. Masson CAPSUM Technologie GmbH

A0031 M. Golghtly THALES Geosolutions-Geotechnics & Engineering Devision

A0032 M. Lykousis Institute of Oceanography, National Centre for Marine Research

A0030 P. Ferentinos Laboratory of Marine Geology and Physical Oceanography, University of Patras

The European continental margins are the focus of increasing human

activities that are moving towards deeper waters. They are witnessing

the greatest technological advances in the world for deep-water

development, in which European industries and academic institutions

are at the forefront. Some of these margins are also a place where

drastic phenomena like slope failures occur, hence questioning the

safety of people and installations. Long term monitoring of

gashydrate deposits is required.

In other respects, some shallow water areas in Europe, surrounded by

densely populated belts and associated infrastructures are located in

seismic zones where the seafloor is also unstable.In both cases, there

is a need to better understand the phenomena leading to these

instabilities. This understanding can be widely enabled by measuring

a set of geotechnical, geodetic or chemical parameters of the sediment

and seafloor. A site must be surveyed in several locations along

failure lines, near a fluid expulsion zone or on a line of change of

slope or a possible presence of gas hydrates. In addition, long term

slow variations of the measured parameters must be detected, this

leads the necessity to have access to both spatial and temporal

variability.

This project proposes to develop, deploy and assess a seafloor

monitoring system, aiming at watching areas of up to one kilometer by

one kilometer, or up to 200 meters down an existing borehole, during

at most two years. The proposed system will be modular enough to fit

the particular topology of a given site of interest. It will allow

near real time data retrieval. The sedimentary processes of interest

in coastal areas and continental margins including slope stability,

creeping, slope failure, fault opening, fluid migration and gas

hydrates, the project will focus on the measurement of pore pressure,

strain of the seabed surface, ground acceleration, ambient noise,

sediment and seawater temperature and seawater current.

The intrinsic properties of the sediment which are not prone to time

variations must be collected with specific means out of the scope of

ASSEM.

The basic principle of the ASSEM project is to deploy instrument

packages at different locations, the sensors being either installed in

available boreholes, or pushed into the unconsolidated sediment, or

simply laid down on the seafloor. The various sensors of a package

are linked to a local data logging and communication unit, forming a

monitoring node.

The various nodes distributed on the instrumented site are then

interconnected through an underwater network using eigher acoustic

communication or cable, depending on the topology. In the same way, a

link depending on the site configuration will be implemented between

one of the nodes and the shore, hence linking all the nodes to an

exploitation station where the data are collected, procesed and made

available to users through the internet.

As a demonstration of the concept feasibility and interest, the

project includes two pilot experiments of approximately nine months

implying close cooperation with the key local actors. One experiment

will be carried out on a selected continental margin site, the other

in a shallow water seismic area. In both cases, the monitoring system

configuration will be adapted to the specific requirements, and the

produced data carefully assessed and exploited by the concerned actors

of the site.

European project :EVK3-2001-00038