MARSITE: Geodetic seabed observatory in the Marmara Sea

The in-situ measurement of seabed displacements remains one of the major challenges of the decade. As an experiment, the LGO laboratory has deployed a network of seabed geodetic stations for 3 years (2014-2018) in the Marmara Sea to measure the movements of a submarine segment of the North Anatolian Fault (2 cm/year), which is a source of recurrent destructive earthquakes on land. This underwater segment, located less than 50 km from the megalopolis of Istanbul, has been free of seismicity since 1766 (last known major earthquake). This seismicity gap would indicate either a continuous asismic movement of the fault of ~2 cm/year or a blocking of the fault which, in case of rupture, could cause a major earthquake.
The principle of the experiment consists of measuring the distance between beacons placed on the bottom on either side of the fault several times a day using acoustics. In 3 years of observation, no movement greater than 5 mm/year was detected. In other words, the fault would be blocked and would have accumulated a slip deficit of around 4 m since 1766. The rupture of this fault could then generate an earthquake of magnitude greater than 7.
This first French experiment in operational seabed geodesy was carried out in collaboration with the GEOMAR Institute in Kiel, the ITU in Istanbul, the LIENSs (La Rochelle) and the CEREGE (Aix en Provence). A new experiment is underway at the foot of Mount Etna, off Sicily, as part of the ERC FOCUS project (2020-2024).