On 17th August and 12th November 1999 the wider area of Yalova, Gölcük, Izmit, Adapazari, Düzce, Kaynasli and Bolu, to the south-southeast of Istanbul (Turkey) was hit by two seismic shocks with magnitude MW = 7.4 and MW = 7.1, respectively. The two events are attributed to reactivation of two adjacent segments of the North Anatolian Fault Zone, a major E-W right-lateral strike-slip fault zone that runs across Turkey. The earthquakes produced surface ruptures over a distance of at least 150 km, as well as settlement, soil fissures, liquefaction, landslides, tsunamis and subsidence. In both cases, the damage distributed was mainly along an E-W aligned zone more than 180 km long and a few km wide. Damage and intensity evaluation followed the EMS1992 and the updated EMS1998 scales. The maximum mtensities approached XII in both earthquakes. Intensity maps show alignment parallel to the strike of the seismic faults, with local variations due to geometry and kinematics of certain tectonic structures. Intensities were considerably amplified locally by accompanying geodynamic phenomena. High intensities were also recorded at long epicentral due to a combination of factors, such as earthquake frequency content, local site conditions and construction type. Finally, intensities exhibited an exponential development in places where the two earthquakes affected the constructions sequentially.
EMS-1998, earthquake, Turkey, tectonics, site effect, concomitant phenomena