Science mission Task 4.3:
Pore water pressure (fluid flow) monitoring and slope stability in seismically active regions
24 month status
The seabed observatory (FluSO) (equipped with seismometer and flow meter) was successfully redeployed inside an active composite pockmark outside Patras harbour, Greece from May 2009- February 2010. The major scientific advance though, is that the results appear to prove that the concept of fluid escape from the seabed related to an earthquake is correct and that sub-seafloor pore pressure changes during seismic activity can be inferred.
18 month status
In the first 12 months of the project NERC led the design and assembly of a seabed observatory
that consists of a flow meter, a seismometer and a data logger inside a large trawl-resistant bottom mount.
The aim of this observatory is to measure changes in fluid escape from the seabed to infer
sub-seafloor pore pressure changes during seismic activity.
Two cruises have been carried out in the first 18 months of the EuroSITES. During this field work
the seabed observatory was first successfully deployed (May 2009) inside an active composite
pockmark outside Patras harbour, Greece and then recovered, serviced and maintained in
September 2009 after a 4 month deployment.
This work was carried out in collaboration with partner HCMR, from their research
vessel RV AEGAIO. In September 2009, upon recovery, the seabed observatory
platform was inspected and serviced (components tested and data downloaded), and then re-deployed at a position closer to the centre of the pockmark.
The new location was chosen to provide a second dataset.
The new experiment should have sufficient battery power for another 3-4 months.
The inspection showed that all parts of the equipment have continually worked without problems and data
was recorded over the entire period.
First analysis of the recorded raw data shows time series of seismic (Figure 1) and flow activity (Figure 2).
Figure 1. Raw data time line of the seismometer data (z-axis)
Figure 2. Raw data time line of the flowmeter data
- Deploy a piezometer in the upper slope (300-500m) at the extended Poseidon-Pylos
site together with an OBS in order to monitor pore water pressure fluctuations.
These will be coupled with the geotechnical properties of the sediments in order to
estimate the regional slope stability. The resulting time series will be important as it
Description of Work EuroSITES Collaborative Project 20
will describe the short-term in-situ variability of sediment pore pressure.
Test the still controversially debated hypothesis that earthquakes trigger submarine
landslides through changes of the pore pressure.
Test the hypothesis that major earthquakes in a marine environment have pre-cursors
in the pore pressure system, which may be used for geohazard warning in the future.
Combine the pore pressure measurements with physical oceanographic data recorded
in the extended Poseidon-Pylos region to integrate the subseabed processes with the
ocean interior processes. Investigate the effect of internal tides (waves) on the
sediment pore pressure to see if they could be another trigger for seafloor failure.
Output:Time-series of pore pressure variations relative to microseismicity