Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the "unexpected" earthquake of 13 May 1995 (<i>M</i><sub>s</sub> = 6.5, NW Greece)

Abstract

Abstract. Seismic hazard assessment and seismicity changes are investigated in the Kozani-Grevena area, at the western margin of internal Hellenides in NW Greece. The region is of great interest, since it was characterized by very low seismic activity until 1995, when the "unexpected" Kozani-Grevena earthquake (M s = 6.5) occurred. This event is of significant importance for Greece, since it, along with the 1999 Athens earthquake, initiated the modification of the Greek Building Code. In order to detect any seismicity changes, the seismicity of the region was divided into three time windows: the first up to 1973, the second from 1900 to 1994 and the third covering the entire instrumental period.For the above mentioned time windows, seismic hazard assessment was performed using the extreme values method. The results indicate an increase of the peak ground acceleration (PGA) values after the impoundment, with the exception of the area in the vicinity of the NE edge of the Dam. Before the occurrence of the 1995 event, the epicentral region also exhibited higher PGA values than before the impoundment. The most significant increase in PGA values is observed SE of the Polyphyto artificial lake, where the largest values are observed for the second and the third period. The coincident increase in the number of earthquakes and in the PGA values may be attributed to the impoundment of the Polyphyto Dam.The maximum expected magnitude is calculated by the extreme values method and Gumbel's third asymptotic distribution. The results reveal similar values of maximum expected magnitudes (M max = 6.5), independent of the seismicity rate, indicating that the 13 May 1995 earthquake was not an "unexpected" event, since the magnitude of an oncoming earthquake depends mainly on the tectonics of the region and the characteristics of the active faults.

Relationship between Observed Seismicity and Water Level Fluctuations in Polyphyto Dam Area (North Greece)

“…During the impoundment of the second Asomata reservoir (October 10, 1984) low seismic activity was observed with few seismic events close to the Asomata lake as well as a seismic activity in the north edge of Polyphyto lake with maximum magnitude ML=5.2 which took place October, 25,1984 in depth=19km in the area between Kozani -Grevena. On the other hand at the beginning of the filling of the third reservoir Sfikia (March 13, 1985) few small earthquakes are observed close to the reservoir during the third and fourth month after the impoundment, as well as a shallow seismic activity with small magnitudes which are located in the south edge of the Polyphyto reservoir.…”

“…This area was classified as low seismicity until 1995, when a strong earthquake of MS=6.5 occurred between the cities of Kozani and Grevena, at a distance of 18 Km from the southern point of the reservoir [19,20,21]. This focal area is near to the earthquake ML=5.2 that took place on 25 October 1984 during the Asomata reservoir initial filling [8,22,23,24,25]. According to several author [26,27,17], many parts of Kozani and Grevena cities and a number of villages had been damaged by the mentioned 1995 earthquake.…”

“…According to several author [26,27,17], many parts of Kozani and Grevena cities and a number of villages had been damaged by the mentioned 1995 earthquake. The latter event caused the disagreement about it was induced due to the first filling of the Polyphyto artificial lake or caused by tectonic movements [28,29,30,31,32,25].…”

Seismic damage scenarios in Lefkas old town (W. Greece)

“…Attenuation relationships or ground motion prediction equations (GMPEs), provide a means of predicting the level of ground shaking and its associated uncertainty at any given site or location, based on parameters such as earthquake magnitude and source-to-site distance. The GMPE that is used in the present study to calculate PGA is the one proposed by Makropoulos (1978) that has extensively been applied in Greece (Makropoulos and Burton 1985b;Papadopoulou-Vrynioti et al 2013;Pavlou et al 2013;Makropoulos et al 2013;Kouskouna and Kaviris 2014):…”

Shear Wave Velocity Estimates through Combined Use of Passive Techniques in a Tectonically Active Area

“…Seismic hazard estimation in recent years has received vast attention from all levels, starting from geo-scientists, civil engineers and policy makers (Hartzell et al 1996, Yamanaka et al 1993, 1994, 1998Köhler et al 2007, Papadopoulou-Vrynioti et al 2013, Pavlou et al 2013, Kassaras et al 2015. The interest in this area is motivated by the notion of minimizing damage by accurate hazard estimation, rather than averting it.…”