Microseismic Activity and Spatial Distribution of Coda-Q in the Westernmost Part of the North Anatolian Fault Zone, Turkey

We carried out a short-term observation of microearthquakes in the seismic gap region in the westernmost part of the North Anatolian fault zone. In this region, the North Anatolian fault zone branches into two fault zones: the Izmit-Sapanca fault zone on the north, and the Iznik-Mekece fault on the south. The results of our analyses are as follows: (1) Microseismic activity was much higher along the Izmit-Sapanca fault zone than along the Iznik-Mekece fault. (2) A fault plane solution of strike-slip type was obtained for a microearthquake along the Iznik-Mekece fault. On the other hand, the solutions of both strik-slip and normal-faulting types were determined for microearthquakes along the Izmit-Sapanca fault zone. (3) Relatively lower coda-Q values were estimated around the Izmit-Sapanca and Iznik-Mekece fault zones, compared with the values in the region north of the fault zones. This attenuation property is considered to be closely related to the inhomogeneity of the crust, probably due to the earthquake faulting along the North Anatolian fault zone. Seen from the above result (2), we may estimate the faulting type of the future large earthquake in the seismic gap region as follows: If it occurs along the Iznik-Mekece fault, it will have a strikeslip mechanism; but if it occurs along the Izmit-Sapanca fault zone, its faulting type may have two possibilities, strike-slip or normal-slip