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, ...

Abstract. The area of Greece has experienced a complex tectonic history dominated by the subduction of the African plate beneath Eurasia. In this study the variations of the crustal thickness in the area of Greece were obtained by means of the multiple-source Werner deconvolution (MSWD) method applied to gravity data. Thicknesses of 40-49 krn are estimated beneath the Hellenides mountain belt to the west. Eastward thinning of the crust, to thicknesses ranging from 25 krn in the north to 30 km in the south is seen in the Aegean region. These results are in good agreement with recent seismological results, demonstrating that the MSWD method successfully treated the problem. Using the crustal model we derived, we computed the gravity effect of the crust and extracted it from the Bouguer anomaly. We also extracted the gravity effect of the subducting lithosphere from the Bouguer anomaly, producing a residual map where most of the original gravity variation has been successfully removed. The remaining anomalies appear related to near-surface features and an area of low-velocity mantle in the central Aegean Sea.

The aeromagnetic data of Macedonia and Thrace were used to produce Curie point estimates. The data were high pass filtered to remove components arising from topography and magnetic core fields which were not adequately modeled by a DGRF. The depth to the centroid, z 0 , of the deepest distribution of the magnetic dipoles was obtained by computing a least-squares fit to the lowest-frequency segment of the azimuthally averaged log power spectrum. The average depth to the top of the deepest crustal block was computed as the depth to the top, z t , of the second lowest-frequency segment of the spectrum. The depth to the bottom of the deepest magnetic dipoles, the inferred Curie point depth, was then calculated from z b ¼ 2z 0 ) z t . The Curie depth estimates for Macedonia and Thrace range between 11.2 and 17.3 km. These results are consistent with the depths inferred by extrapolating known geothermal gradient and heat-flow values.

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