Improved detection and Coulomb stress computations for gas-related, shallow seismicity, in the Western Sea of Marmara

The Sea of Marmara (SoM) is a marine portion of the North Anatolian Fault (NAF) and a portion of this fault that did not break during its 20th century earthquake sequence. The NAF in the SoM is characterized by both significant seismic activity and widespread fluid manifestations. These fluids have both shallow and deep origins in different parts of the SoM and are often associated with the trace of the NAF which seems to act as a conduit. On July 25th, 2011, a M-w 5 strike-slip earthquake occurred at a depth of about 11.5 km, triggering clusters of seismicity mostly located at depths shallower than 5 km, from less than a few minutes up to more than 6 days after the mainshock. To investigate the triggering of these clusters we first employ a match filter algorithm to increase the number of event located and hence better identify potential spatio-temporal patterns. This leads to a 2-fold increase in number of events relocated, coming mostly from the shallow seismic clusters. The newly detected events confirm that most of the aftershocks are shallow, with a large number of events located in the first few km below the SoM seafloor.