Interplay between fluids, seismic and aseismic deformation concurrently to a Mw 4.6 earthquake in the western part of the Sea of Marmara

Summary The North Anatolian Fault (NAF) in the Sea of Marmara is characterized by varying mechanical behaviors and fluid manifestations along its path. In the present study, we investigate an earthquake sequence including a Mw 4.6 earthquake that occurred on November 27, 2013, in the partially creeping section of the NAF in the Sea of Marmara. Using onshore and offshore seismic data from October 2013 to August 2014, we document a sequence of highly-similar events prior to this earthquake, occurring within a zone where repeating earthquakes, likely indicative of creep, have been previously identified. This sequence coincides with the recently proposed existence of a several months-long slow-slip event (SSE) propagating westwards along the main fault trace at a rate of ∼0.5 km/day, based on the interpretation of onshore geodetic data and offshore surface sediment pore pressure data. The timings of the multiplet (i.e., the highly similar events), mainshock and decreases in pore pressure measured within the fault valley are compatible with the hypothesis that the SSE impacted first the multiplet-mainshock sequence and then the sub-seafloor hydrological network within the fault valley. Models of the SSE as a slipping patch propagating westward with a combination of right-lateral slip and tensile opening, show an increase in Coulomb stress of a few tenths of kPa at the position of the mainshock sequence. Despite limited calculated Coulomb stress transfer due to the SSE, our observations suggest that complex hydromechanical interactions exist between splay faults, such as those where the mainshock occurred, and the main NAF, and underline the interest of using multi-disciplinary data to study relationships between fluids and fault deformation.