Current accelerating seismic excitation along the northern boundary of the Aegean microplate G.F. Karakaisis * , C.B. Papazachos, E.M. Scordilis, B.C. Papazachos Geophysical Laboratory, School of Geology, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece Received 17 January 2003; accepted 8 March 2004 Available online 26 April 2004 Abstract According to previous observations [Geophys. Res. Lett. 27 (2000) 3957], the generation of large (M z 7.0) earthquakes in the western part of the north Anatolian fault system (Marmara Sea) is followed by strong earthquakes along the Northern Boundary of the Aegean microplate (NAB: northwestermost Anatolia – northern Aegean – central Greece – Ionian islands). Therefore, it can be hypothesized that a seismic excitation along this boundary should be expected after the occurrence of the Izmit 1999 earthquake (M = 7.6). We have applied the method of accelerating seismic crustal deformation, which is based on concepts of critical point dynamics in an attempt to locate more precisely those regions along the NAB where seismic excitation is more likely to occur. For this reason, a detailed parametric grid search of the broader NAB area was performed for the identification of accelerating energy release behavior. Three such elliptical critical regions have been identified with centers along this boundary. The first region, (A), is centered in the eastern part of this boundary (40.2jN, 27.2jE: southwest of Marmara), the second region, (B), has a center in the middle part of the boundary (38.8jN, 23.4jE: East Central Greece) and the third region, (C), in the westernmost part of the boundary (38.2jN, 20.9jE: Ionian Islands). The study of the time variation of the cumulative Benioff strain in two of the three identified regions (A and B) revealed that intense accelerating seismicity is observed especially after the occurrence of the 1999 Izmit mainshock. Therefore, it can be suggested that the seismic excitation, at least in these two regions, has been triggered by the Izmit mainshock. Estimations of the magnitudes and origin times of the expected mainshocks in these three critical regions have also been performed, assuming that the accelerating seismicity in these regions will lead to a critical point, that is, to the generation of mainshocks. D 2004 Elsevier B.V. All rights reserved. Keywords: Accelerating seismic deformation; Aegean; Earthquake prediction 1. Introduction The Aegean area (34jN–43jN, 19jE–30jE) is seismically the most active area of western Eurasia. This is mainly due to the existence and fast south- westward motion of the Aegean microplate with respect to the Eurasian plate (McKenzie, 1970, 1978; Oral et al., 1995; Papazachos, 1999). In the south, this microplate is bounded by the Hellenic Arc (Zante–Crete–Rhodos) where it overrides the east Mediterranean lithosphere (front part of the 0040-1951/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2004.03.005 * Corresponding author. E-mail address: karakais@geo.auth.gr (G.F. Karakaisis). www.elsevier.com/locate/tecto Tectonophysics 383 (2004) 81– 89