Abstract
A probabilistic approach was applied to map the seismic hazard in Greece and the surrounding region. The procedure does not require any specification of seismic sources or/and seismic zones and allows for the use of the whole seismological record, comprising both historical and instrumental data, available for the region of interest. The new seismic hazard map prepared for Greece and its vicinity specifies a 10% probability of exceedance of the given Peak Ground Acceleration (PGA) values for shallow seismicity and intermediate soil conditions for an exposure time of 50 years. When preparing the map, the new PGA attenuation relation given by Margaris et al. (2001) was employed. The new map shows a spatial distribution of the seismic hazard that corresponds well with the features of shallow seismicity within the examined region. It depicts the level of seismic hazard in which the exceedance of the PGA value of 0.25 g may be expected to occur within limited areas. The highest estimated levels of seismic hazard inside the territory of Greece are found in the Northern Sporades Islands, where PGA values in excess of 0.50 g are reached at individual sites, and in the Zante Island in Western Greece, where PGA values in the range of 0.35 g to 0.40 g are obtained at more numerous localities. High values are also observed in the sea between the Karpathos and Rhodes islands, near the Island of Amorgos (Cyclades Archipelago) and in the Southwestern Peloponnesus. The levels of seismic hazard at the sites of seven Greek cities (Athens, Jannena, Kalamata, Kozani, Larisa, Rhodes and Thessaloniki) were also estimated in terms of probabilities that a given PGA value will be exceeded at least once during a time interval of 1, 50 and 100 years at those sites. These probabilities were based on the maximum horizontal PGA values obtained by applying the design earthquake procedure, and the respective median values obtained were 0.24 g for Athens, 0.28 g for Jannena, 0.30 g for Kalamata, 0.21 g for Kozani, 0.24 g for Larisa, 0.43 g for Rhodes and 0.35 g for Thessaloniki. The probabilities of exceedance of the estimated maximum possible PGA value were also calculated for the cities to illustrate the uncertainty of maximum PGA assessment.
Highlights
The basic lithospheric process in the Aegean Sea is the subduction of the African plate under the Eurasian plate south of the Island of Crete, forming the Hellenic Arc and Trench (Papazachos and Comninakis, 1971; Comninakis and Papazachos, 1972; Makris, 1973; Mercier, 1977; McKenzie, 1978; Dewey and Sengor, 1979; Makropoulos and Burton, 1984)
Most of the zone of increased seismic hazard corresponding to the Hellenic Arc and Trench, as well as the North Aegean and Western Turkey, shows Peak Ground Acceleration (PGA) values in the range of 0.20 g to 0.25 g, while values in excess of 0.25 g are reached within limited areas
The maximum computed PGA values inside the territory of Greece are in excess of 0.50 g and can be found at individual sites in the Northern Sporades Islands, whereas PGA values in the range of 0.35 g to 0.40 g are obtained at more numerous localities in the Ionian Islands
Summary
The basic lithospheric process in the Aegean Sea is the subduction of the African plate under the Eurasian plate south of the Island of Crete, forming the Hellenic Arc and Trench (Papazachos and Comninakis, 1971; Comninakis and Papazachos, 1972; Makris, 1973; Mercier, 1977; McKenzie, 1978; Dewey and Sengor, 1979; Makropoulos and Burton, 1984). A seismic hazard map was created for the Greek territory In this map, the estimated seismic hazard is specified in terms of the PGA with a 10% probability of exceedance in 50 years, corresponding to a return period of 475 years. A detailed analysis of seismic hazard was carried out for the Greek cities of Athens, Jannena, Kalamata, Kozani, Larisa, Rhodes and Thessaloniki This included an assessment of the maximum possible PGA at the sites of the cities and the calculation of the probabilities that a given PGA value will be exceeded at least once during time intervals of 1, 50 and 100 years at each site. The probabilities of exceedance of the maximum possible PGA values were calculated to illustrate the uncertainty of maximum PGA estimation
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