The North Anatolian Fault Zone (NAFZ) below the Sea of Marmara forms a "seismic gap" where a major earthquake is expected to occur in the near future. This segment of the fault lies between the 1912 Ganos and 1999 Izmit ruptures and is the only NAFZ segment that has not ruptured since 1766. To monitor the microseismicactivity at the main fault branch offshore of Istanbul below the C narck Basin, a permanent seismic array (PIRES) was installed on the two outermost Prince Islands, Yassiada and Sivriada, at a few kilometers distance to the fault.