High-Resolution Seismic Analysis of the Marmara Sea: Microseismic Activity from OBS Data and Nearly-Repeating Earthquakes

The Main Marmara Fault beneath the Marmara Sea constitutes a major seismic gap capable of generating a large earthquake, posing a serious hazard to the region and its surroundings. Consequently, detailed characterization of seismicity and its relationship to fault-zone deformation is essential. One of the primary objectives of this study is to compile a seismicity database for the Marmara Sea covering the period 2014–2016, based primarily on data recorded by ocean-bottom seismometers.

The detected and relocated seismicity reveals distinct spatial and depth-dependent patterns among the Marmara basins. The Tekirdağ Basin is characterized by diffuse seismicity at depths of approximately 7–18 km. In contrast, the Central Basin exhibits a high rate of microearthquake activity between 3 and 15 km depth. The Kumburgaz Basin and the western part of the Çınarcık Basin, show sparse seismicity within depth ranges of 5–19 km and 3–18 km, respectively.

Previously identified repeating earthquakes were searched  using a template-matching approach applied to continuous seismic waveforms spanning a larger time frame of 2008–2021. Clusters of highly correlated earthquakes that occur closely in time or partially overlap are classified as near-repeating events. The Central Basin displays clear signatures of seismic creep, marked by both elevated seismicity rates and the presence of nine near-repeating earthquake clusters. Focal mechanisms of these clusters indicate dominantly strike-slip motion, consistent with the kinematics  of the Main Marmara Fault. Two distinct recurrence patterns are observed among the near-repeaters, representing short-term and long-term repeating behaviors. Slip-rate estimates derived from these clusters vary spatially but are broadly comparable to geodetic slip rates.