Long-term in situ observations at the Athina mud volcano, Eastern Mediterranean: Taking the pulse of mud volcanism

Long-term monitoring on mud volcanoes is fundamental to unravel episodic processes and transient changes that might otherwise be missed by using snapshot observations during time-limited research expeditions. We deployed a pore- and seafloor-pressure observatory close to the main conduit of the Athina mud volcano, south of Turkey (Eastern Mediterranean Sea), for a period of 26 months between February 2014 and April 2016. The observatory recorded 32 pore pressure transients related to as many seismic events (out of 625 earthquakes with Mw >= 2.5 occurred over the monitoring period in a radius of 1000 km) and few pore pressure excursions related to mud volcanism. The data helped to define a threshold for earthquake-triggered changes in mud volcano pore pressure, thus delineating possible pore pressure-distance relationships for different magnitudes ranges. Peak ground accelerations, as representative for earthquakes ground motion at the observatory have been calculated with different ground motion prediction equations. Using a conservative approach, an empirical equation has been identified, which specify the lowermost PGA necessary to induce a change in pore pressure record at the Athina mud volcano. Moreover, internal variations of the mud volcano system recordable through the pore pressure signal have been described for the first time in such a submarine feature.