Background Information
The North Anatolian Fault, on which destructive earthqukes frequently occur, is a 1300 km long, 10 – 100 m wide right lateral active fault lying between Karlıova in the east and Gulf of Saros in the west. The fault, together with the East Anatolian fault, forms the most active elements of the tectonic structure of the Anatolia. Starting from 1939 Erzincan earthquake, a migration of earthquakes on the fault was observed. The 1999 earthquake formed the latest chain of this migration, the penultimate being the 1967 Adapazarı earthquake. The Active Fault Map of Turkey (Saroglu, F., Emre, O and Kuscu, I., 1992) shows the active faults in the country, at a scale of 1:1 000 000, considering the faults that have moved or likely to move since Quaternary are active since no more detailed classification is not made till now. In context of a marine geology and geophysics project, supported by TUBITAK and carried out by MTA, Cambridge University and İstanbul Technical University, submarine faults in Sea of Marmara were mapped. The map is based on 1500 km seismic profiles recorded on board MTA Sismik-1 research vessel. Although corrections and datailed analyses needed, this preliminary map was brought under light upon this emergency case, to the attention of earth scientists.
Active Fault Map Of Turkey
Scale: 1/2.000.000
Map of Submarine Faults (Marmara Sea; MTA, Cambridge U., ITU)
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. İzmit-Adapazarı 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.
The Active Faults In And Around The Area (Modified from Emre et al. 1998)
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