Relative Locations of Clustered Earthquakes in the Sea of Marmara and States of Local Stresses in the East of the Central Marmara Basin

We relocate 27 small earthquakes and invert the state of stress in the East of the Central Marmara basin through re-identification of P and S phases using a joint data set. Also, we derive relative locations of 425 clustered earthquakes with ML ≥ 1.5 in the Marmara Region using the Hypodd software. The main objective is to achieve the definition of geometrical orientations and seismic behaviours of the fault segments. Locating between the 1912 Mürefte and 1999 Izmit earthquakes and being a seismic gap, seismic and geodetic analyzes in the Central Marmara Sea are significant. We use well-defined P and S phases for locations, and completely observable P-wave first motion polarities (FMPs) for simultaneously determined individual fault plane solutions (FPSs) and stress orientations. We get data from 105 seismic stations, including 5 continuous OBSs; hence, each FPS has at least 10 FMPs and maximum 1 inconsistent station. We observe normal and oblique focal mechanism solutions, and a NE-SW trended extensional state of stress in the Eastern Central Marmara by this comprehensive research, although the main Marmara Fault, the western branch of the North Anatolian Fault Zone (NAFZ), is dominated by a right lateral strike-slip regime. Due to the use of a dense network, we observe neither horizontal nor vertical large shifts in the locations of earthquakes: a total of 398 out of 425 are from Korkusuz Öztürk et al. (Tectonophysics 665:37–57, 2015), after the relative relocation process. As a result, we could not observe fault dip angles clearly, but define seismic zones for each segment which has not been done before for many segments in the Sea of Marmara, and interpret current stress loads. Consequently, our sensitive relocations and stress tensor inversion analyses will make an important contribution to a better understanding of the fault movements in the Sea of Marmara, and shed light on especially earthquake rupture and tsunami analyses.