FIELD OBSERVATIONS

     An earthquake occurred in eastern section of Sea of Marmara Region in NW Turkey in August 17th, 1999 at 03:02 am. It took place on the northern flank of the North Anatolian fault, one of the well known seismic right lateral strike-slip fault of the World.

     The earthquake was the last one of a series of westward  migrating earthquakes on the fault starting from 1939 Erzincan Earthquake in the eastern section of the fault. Historical records show that the similar migrations took place in the past.
The next after the event, MTA Geologists (Dr. Omer Emre and  Dr. Tamer Y. Duman) reached the area and made field observations in the areas as much as possible due to the extent of damages and bad road conditions.

     Four segments in the area were observed to faulted.  These are,

1. �zmit-Adapazar�; Segment: Total length is 90 km. Of that, 40 km on land is totally  ruptured. Along its submarine continuation, large sea waves are reported. Offset on this segment is reported to be 290+-10cm.
2. Gölcük Segment: Ground ruptures observed but due to rescue activities not accessed. Amateur scuba divers observed submarine cracks along the fault line. Many houses and buildings slided down to sea bottom and sea invaded the shore. Vertical offset can be taken into consideration.
3. Yalova Segment: No ground ruptures on land could be traced. Submarine faulting.
4. Düzce Segment: Not reached yet. Seismologic and macroseismic data indicates faulting.