Tomography of the crust and upper mantle in southeast Europe

Abstract

Compressional velocity structure of the crest and the upper mantle in southeastern Europe (broader Aegean area) is studied by inverting residuals of the first P arrivals from earthquakes in this region (16øE-3 IøE, 34øN43øN). The.dam used are from regional events recorded by the permanent network of stations during the period 1971-1987, enriched with data from experiments with portable seismogmphs in four regions of this broad area. This study confirms the strong variations of crustal thickness in this area as well as the subduction of the eastern Mediterranean lithosphere under the southern Aegean and gives further detailed information on the crustal anti upper mantle structure of the area. Important new information is the existence of a low-velocity crustal layer in western Greece and Albania and that the velocity anomaly in the mantle under the southern Aegean extends much farther and deeper to the northeast than the Benloft zone of the intermediate depth earthquakes indicates. Furthermore, evidence is presented about the possible existence of older subduct. ion in the northern Aegean and about the influence of the tectonic regime on the velocity field. Paper number 95JB00669. 0148-0227/95/95J-B.00669505.00 continuation in the northern Aegean together with ttie North Aegean Trough (Figure 1). Contours of average depth of 100 and 160 km intermediate depth earthquakes in the southern Aegean [Papazachos, 1990] are also shown in Figure 1. The velocity structure of the crust and upper mantle in this area has been studied using travel times from local earthquakes [Papazachos et al., !966; Panagiotopoulos. anal Papazachos, 1985] or explosions [Makris, 1972, 1978• Voulgaris, 1991 ], dispersion of surface waves [Papazachos et al., 1967; Calganile et al., 1982], and gravity data [Makris, 1973; Chadas et al., 1992]. A preliminary Moho map of the area based on all the previously published studies is presented in Figure 2 [Papazachos, 1993]. Strong variations of crustal thickness are observed. The ernst is moi'e than 40 km thick under the Dinarides-Hellinides mountain chain but is 1Qcally thinning to less than 25 km in the back are area (Aegean Sea). This thinning, which is also confirreed by gravity studies [Makris, 1976; Chailas et al., 1992; Papazachos, 1994], is mainly attributed to the back ate spreading of the Aegean Sea. The first results from seismic tomography were presented only recently and allowed a more detailed description of the lithosphere and the mantle. These previous studies [$pakman, 1986, 1988; $pakman et al., 1988, 1993; L•gdas et al., 1990; Ligdas and Main, 1991] tried to establish the principal features of the lithosphere-upper mantle system, to a depth of 800 km or more. Other studies concentrated on more local scales [Drakatos, 1989; Drakatos eta].]. The large-scale structure of the crust and uppermost mantle has not been studied in detail. In all the regional studies, the crust is treated as one layer [Drakatos and DrakopouIos, 1991; Ligdas et al., 1990] or as a part of the first layer [$pakman, ...

Kinematics of the Southern Rhodope Core Complex (North Greece)

“…It assumes that the Chalkidiki Peninsula and most of the Bulgarian Rhodope represent the upper brittle crust since the middle Eocene. The Moho is drawn after Papazachos et al (1995) and Papazachos (1998). Crustal thickness at each step of the restoration is obtained from area balancing of the ductile crust estimated from the present day shape of the SRCC.…”

Rayleigh wave group velocity tomography in the Aegean area

“…The crust has a normal thickness (28 -37 km) in the eastern part of the Greek peninsula, in the Northern and Central Aegean, in Western Turkey and in Crete. An overall description of the lithosphere and upper mantle is given by early tomographic studies (Spakman, 1986;Spakman et al, 1988Spakman et al, , 1993Ligdas et al, 1990;Ligdas and Main, 1991;Drakatos, 1989;Drakatos et al, 1989;Christodoulou and Hatzfeld, 1988;Ligdas and Lees, 1993;Papazachos et al, 1995). Recently, Papazachos and Nolet (1997), using travel time data from local earthquakes in Greece and surrounding areas, presented detailed results for the structure of the Aegean lithosphere.…”

Microseismic activity and seismotectonics of Heraklion Area (central Crete Island, Greece)

“…1), the island of Crete is considered as an area of important tectonic deformation and high seismic activity, resulting from the collision between the Eurasian and African plates and the subduction of the latter under the former (McKenzie, 1972(McKenzie, , 1978Papazachos, 1973; Ange-Ł Corresponding author. Tel.=Fax: C30 1 7247445; E-mail: nvoulgar@atlas.uoa.gr lier, 1979;Papadopoulos et al, 1986;Spakman et al, 1988;Drakatos and Drakopoulos, 1991;Papazachos et al, 1995;Alessandrini et al, 1997;. As a result of this complex tectonic deformation several damaging earthquakes have occurred since historical times (Papazachos and Papazachou, 1997).…”