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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
rank the relative risk from different scenarios. These resulting
maps should be used for the tsunami impact in relations to the
natural environment, land use/land cover types and road
network.
One should not forget that a local tsunami generally produces
run-up significantly higher than that of a distant generated
tsunami, provided that the source earthquakes were of similar
magnitude. Therefore, the tsunami waves may be destructive
along the Marmara coasts of Istanbul and for shallower areas
(x20 m). The effect of tsunami can be minimised on flat coastal
plains (c.g. Cekmece lagoons, Ayamama, Bakirkóy, and
Zeytinburnu) by planting tree belts between shorelines and
areas needing protection. At Büyükcekmece lagoon and in
small harbours or marinas, very strong currents and extensive
damage to property may occur if the tsunami amplitude is more
than 2m. It may also be expected loss of life in addition to
general loss of property, if the runup exceeds 2.5 metres.
Constructing breakwaters at harbours entrances, avoidance of
potential areas for settlement and having streets aligned
perpendicular to the wave advance may solve such problems.
Our inundation mapping efforts depend upon the numerical
tsunami modes based on the landslide and slump hazards in the
Sea of Marmara. Such kind of models developed for tsunami
generation, propagation and coastal amplification are not
enough to know the maximum run-up with any certainty. On
the basis of new marine surveys, shallow water models should
be developed and upgraded to a better convenient faster
accurate level. Simulation of historical events is important.
Comparisons between simulated results and other observations
allow the first estimation of the source energy.
A monitoring system for acquisition of seismic signal and water
level displacement simultaneously must be installed to
favouring the study of the tsunami generation in a selected area.
At least two digital mareographic stations based upon a
submerged pressure gauge and a micróbarograph must be
installed; one in the imrali island.
The rises in sea level from storms at the time of an actual
tsunami could change the run-up elevation by + 1-1.5 m from
the mean sea level assumed in the simulation. This would also
make significant changes in the horizontal position of the
inundation lines.
Narrow estuaries and straits may maintain or amplify the wave
height of open coastal tsunamis. Wave propagation modelling
studies are suggested for the Strait of Istanbul and the Golden
Horn estuary. The coastal run-up is assumed to decrease inland
in barrier-protected bays and estuaries. Experiments showed
that a run-up is locally higher if the tsunami partially or
completely overtops the barrier, strikes a shoreline directly
behind the entrance to an estuary, or enters a constriction in the
estuary. Such errors should be added to the average run-up
value to obtain the final run-up elevation.
In future, if any area is found to be underlain by deposits
inferred to be from historic or prehistoric tsunamis, these areas
should be included in the inundation boundaries we have
defined. Since tsunamis can inundate without leaving behind a
sediment deposit, presence of deposits was considered a good
indication of minimum inundation.
701
Acknowledgement
Authors thank to INTA SpaceTurk that supplied the IKONOS
data of the Istanbul coasts along the Sea of Marmara.
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