HISTORICAL SEISMICITY, PALEOSEISMICITY AND SEISMIC RISK IN WESTERN MACEDONIA, NORTHERN GREECE

Western Macedonia, Northern Greece, was a seismically quiescent region for one or more centuries, and was regarded as a nearly aseismic, rig id block inside a broad zone of distributed continental deformation an d faulting, and a region of minimum seismic risk. Consequently, the Ma y 13, 1995 destructive earthquake (M = 6.6) which hit this assumed ase ismic zone was a surprise for scientists, government and population. H owever, historical and archaeoseismic evidence, as well as coastal cha nge data indicate that the assumed aseismic region of Western Macedoni a has been affected in the last 2,000 years by at least seven, and pos sibly nine destructive earthquakes. One of these earthquakes occurred in cir ca 1700, and probably had the same epicentre with, but higher m agnitude than the 1995 shock. The earthquake in circa 1700 is deduced from historical data and is modelled on the base of a swarm of church repairs which is explained as post-seismic recovery of the broader Koz ani area: except for certain well known cases of towns or areas in whi ch religious privileges were granted, large scale repairs or reconstru ction of churches during the Ottoman period were possible only after S ultan's permissions, usually following earthquakes and other calamitie s. It can hence be concluded that some, at least, of the apparently as eismic regions inside broad zones of distributed seismicity are hit by stronger shocks, but with longer (200 years or more) recurrence inter vals than their adjacent zones. Consequently, the seismic risk of the apparently aseismic regions is certainly not low, especially since rel atively long periods of seismic quiescence lead to constructions vulne rable to earthquakes. (C) 1998 Elsevier Science Ltd. All rights reserv ed.