Probabilistic Seismic Hazard assessment in Albania

Albania is one of the coutries with highest sesimicity in Europe.The history of instrumental monitoring of seismicity in this country started since 1968 with the setting up of the first seismographic station of Tirana and more effectively after the beginning of the operation of the Albanian Seismological Network in 1976. There is a rich evidence that during two thousands years Albania has been hit by many disastrous earthquakes. The highest magnitude estimated is 7.2. After the end of Communist era and opening of the country, a boom of constructions started in Albania continuing even now. It makes more indispensabile the producing of accurate seismic hazard maps for preventing the damages of future probable earthquakes. Some efforts have already been done in seismic hazard assessment(Sulstarova et al., 1980; Kociu, 2000; Muco et al., 2002). In this approach, the probabilistic technique has been used in one joint work between Seismological Institute of Tirana, Albania and Department of Geophysics of Aristotle University of Thessaloniki, Greece, into the framework of NATO SfP project "SeisAlbania". The earthquake catalogue adopted was specifically conceived for this seismic hazard analysis and contains 530 events with magnitude M>4.5 from the year 58 up to 2000. We divided the country in 8 seismotectonic zones giving for them the most representative fault characteristics. The computer code used for hazard calculation was OHAZ, developed from the Geophysical Survey of Slovenia and the attenuation models used were Ambraseys et al., 1996; Sabetta and Pugliese, 1996 and Margaris et al., 2001. The hazard maps are obtained for 100, 475, 2375 and 4746 return periods, for rock soil condition. Analyzing the map of PGA values for a return period of 475 years, there are separated 5 zones with different escalation of PGA values: 1)the zone with PGA (0.20 - 0.24 g) 1.8 percent of Albanian territory, 2)the zone with PGA (0.16 - 0.20 g) 22.6 percent of Albanian territory, 3)the zone with PGA (0.12 - 0.16 g) 26.5 percent of Albanian territory, 4)the zone with PGA (0.08 - 0.12 g) 28.2 percent of Albanian territory and 5)the zone with PGA (0.04 - 0.08 g) 21.9 percent of Albanian territory. The new maps of probabilistic seismic hazard for Albania would be a basic tool for the strategies of seismic hazard mitigation in this country.