THE TSUNAMI THREAT IN THE SEA OF MARMARA, TURKEY: A REVIEW

摘要

Review of the available data suggests that there is a threat of tsunami inundation to the coasts of the Sea of Marmara and Gulf of Izmit. The tsunami may be the result of shaking from the next major earthquake or more probably, the secondary effect of sediment slumping on the seabed. This assessment is based on the extensive historical database available for the region and is supported by earthquake probability analysis, geological interpretation of the offshore area and preliminary mathematical simulations. In spite of the evidence, there are still too few focussed tsunami studies, and thus tsunami source mechanisms, propagation and onshore run-up remain poorly researched and largely unknown. The most recent tsunami event was associated with the Izmit earthquake of August 1999, when a tsunami wave up to 6.0 metres high inundated the coastal areas in the central part of the Gulf of Izmit. By contrast, earthquake risk has been well studied. The probability of a progressive westward shift in major earthquakes along the east-west trending North Anatolian Fault over the past 60 years indicates that the next major shock will be located offshore in the eastern part of the Sea of Marmara or the Gulf of Izmit. An earthquake located offshore in the eastern area will almost certainly generate a tsunami that will attack the eastern coasts, some of the most populated and industrial areas of Turkey. The areas most threatened by tsunamis are in the eastern Sea of Marmara and Gulf of Izmit. The southern areas of Istanbul would be at risk. An assessment of the limited database available suggests that the sediment slumps located on the marginal slopes of the deep basinal areas of the Sea of Marmara as well as the deeper areas of the Gulf of Izmit are probable tsunami source locations. A tsunami sourced from any of these basins has the potential to strike surrounding coasts but its magnitude will depend on the actual source location, propagation direction and local run-up. The tsunami source will be seabed displacement either by faulting or, more probably, sediment slumping.