Understanding whether slow slip along fault boundaries is likely to eventually cause a high-magnitude earthquake is essential in assessing seismic hazards. A study recently published by Ifremer in the journal Nature Communications clearly characterizes the phenomena associated with slow earthquakes further to the analysis of water pressure in marine sediments.
Under the Sea of Marmara, less than 50 kilometres from the city of Istanbul, runs the so-called North-Anatolian fault, responsible for a series of earthquakes which have had devastating effects on the region. In this particular zone, low-magnitude slow earthquakes, called SSE for Slow Slip Events, occur at the tectonic boundary between Anatolia and Europe.
In an attempt to explain their origin and identify the consequences of episodic slow slipping, Ifremer researchers have deployed piezometers in this region to measure water pressure in marine sediments and used terrestrial GPS stations for detecting and measuring tectonic deformations.
The study shows a correlation between fluctuating water pressure in marine sediments and onshore deformations during a 10-month slow-slip event. The piezometer has consequently become the «thermometer» of this type of slow-slip process.
« Thanks to the easy-to-use surface sensors, we were able to observe events that take place several kilometres below the bottom of the sea. Our data provides important information on the slow slip of the North Anatolian fault. This has enabled us to follow the evolution and analyse the consequences of this creep over a period of 10 months» confirms Nabil Sultan, geotechnical researcher at Ifremer.
The seismic activity is slowly moving closer to Istanbul
The North Anatolian fault crosses Turkey over a distance of more than a thousand kilometres. Its history began around fifteen million years ago with the collision between the Arabian and Eurasian plates, which currently converge on the eastern edge of the Mediterranean. In 1999, the Izmit earthquake, east of the Marmara Sea, ruptured 140 kilometres of fault. Three months later, the Düzce quake extended this fracture by 35 kilometres. This seismic, geographical and temporal singularity makes a major event almost inevitable, provoking in turn an earthquake of considerable violence in the megalopolis of Istanbul.