ΔΗΜΟΣΙΕΥΣΗ Νο 9a

FOUNTOULIS, I. (1989). - The present Geodynamic regime of the Hellenic territory. In: Guidebook for Excursion για το IGCP Project No 250. Aθήνα-Καλαμάτα, 30 Σεπτ. - 8 Οκτωβρ. 1989, p. 8-15.

THE PRESENT GEODYNAMIC R E G I M E OF THE HELLEN1 C TERRITORY

The present Hellenic orogenic arc is restricted only at the s o u t h e r n p a r t of the Hellenic territory, in c o n t r a s t with all the previous ones, which were developed throughout the whole length of t he Hellenides.

During Middle Miocene, a p a r t of the Hellenic arc. which today is active, w a s cut from the Tethyan chain and, since then, it followed its own evolution.

To the north, this p a r t is bounded by the prolongation of the so-called Anatolian f a u l t , which shows a dextral horizontal component of movement. In t h e n o r t h e r n Aegean region, this fault coincides with the northern limit of the active part of the Hellenic arc, for which the term Aegean microplate has been used (McKENZIE 1970, 1972, 1978, GALANOPOULOS 1972) .

The Hellenic arc reaches gradually its present geometry s i n c e the Late Miocene. The back-arc basin, as well as the volcanic a r c , are restricted at the Aegean plate region 1 . e . s o u t h e r n of the Sperchios graben and western of the Turkish coast (fig. 1).

According to LE PICHON et a1 (1981). the present geodynamic regime of the Hellenic arc is characterized by an assyrnetry of i t s movement: along the Ionian trench the direction is NE-St3 and the regime is purely compressional, which is in accordance to the f a u l t plane solutions while, in the Pliny and Strabo trenches, t h e direction of movement is composite, featuring a substantial dextral horizontal component along a NNE-SSW direction ( f i g . 2) .

In the region behind the arc , extensional structures exist. which usually a re apparent and a very important horizontal component of movement coexists.

Many geodynamic models have been proposed for the Hellenic arc and especially for Peloponnesus. These models accept t h a t Peloponnesus is under extensional stress field, accompanied by tectonic grabens which have created by normal faulting in the back arc basin (RITSEMA 1974, McKENZIE 1978, MERCIER 1979, LE PICHON & ANGELIER 1979, DEWEY & SENGOR 1979 and o t h e r s ) .

* Department og Geology, University of Athens Panepistimioupolis Zografou, 157 84, Athens Greece

Fig.1 Schematic reconstruction of t h e Hellenic orogenic Fig. la McKenzie's models arc during Oligocene- Quaternary.(after PAPANIKOLAW

f o r the Aegean

and DERHfTZlKIS. 1981)

Fig. 2 Schematic reconstruction of t h e kinematic in the Hellenic a rc , in the western part of which subduction - abduction dominates, while in the eastern p a r t sinistral horizontal movement dominates (based o n data of LE PICHON & ANGELIER, 1979, LE PICHON et al, 1979). The thin lines indicate the direction of the principal compression based on the fault plane solution of the b ig earthquakes ( a f t e r PAPANXKOLAOU, 1986). 9

mUTH WESTERN TUESSALY SPERtHOS OCn-PARHAS505

WESTERM COR!NWI*H C R E TAM

VALLEY GULF WESlERN

BASlH

MesaarM

Fig. 3 The neotectonic structure of the Aegean Region in longitudinal to t h e Alpine chain section. The t e c t o n i c dipoles w i t h , their t i lting townrcts the SE are brief ly illustatad (after PAPANIKOLAOU and DERMITZAKIS,1979)

Fig. 4 The neotectonic map of the main marginal f a u l t zones of the post-alpine basins in the southern continental Greece (a) and the neotectonic fault p a t t e r n of the Hellenic arc (af ter MARIOLAKOS et a l , 1985) .

Fig. 5 Gravity difference map o Peloponnesus f o r the period 1968 to 1981; contour interval 10 ugals (a f t er MARIOLAKOS et a l , 19851.

Fig. 6 Map showing the shallow seismicity of Peloponnesus and adjacent areas f o r 1968 t o 1981. Rectangles outline the areas where the epicenters have been calculated f o r the histograms in Figure 76 (after FIARIOLAKOS e t al, 1985).

.-- WSW ENE

F i g . 7 Cross sect ions a l m g tha (B-31) and ENE-WSW (A-A= 1 profiles correlating geological and geophysical data.

a) Morphotectonic section. bl Variation of the tectonic distortion deduced from

the map of Figure 5 . The scale of the degree of the tectonic distortion has been taken as proportional to the gradient of the gravity differences along the profile.

c) Representative movements of the tectonic dipoles.

dl Distribution of t h e earthquake focus deduced f r a the of Figure 6 .

F i g . 8 Analysis of t h e general stress f i e l d F based on t b faults of the three parts ( I , 11, 111) of F i - 4 pure ((11 and shearing (T,) components. In the uppsr l e f t part of the picture the NW Pe loponnesua region $8 analyzed (under magnification). The faults mre developing with a substantial horizontal sinistral component and a dextral rotation of the part in between. The relatively non-seismic Cyclades region in dominated by NW-SE oriented f a u l t s . f n these faults. the shear cotmwmnt tTal of t h e general stress f i e l d is negligible.

MARIOLAKOS (1976, 1979) proposed the tectonic dipole: a tectonic multiblock which has differential movement at i t s edges (fig. 3 ) .

MARIOLAKQS & PAPANIKOLAOU (1981) suggest t h a t the configuration of the Neogene basins is contro 1 led by marginal f a u l t zones. These f a u l t zones create an assmetry to the deposits, the relief and the structure, in every basin. According to them. the Hellenic a r c is separated in three large pa r t s ( f i g . 4). In part T the big fault zones have an E - W direction. In part 11 the direction is NW - SE and in part 111 the direction changes to NE - SW. This arrangement shows that on ly parts 11 and I I I have apparent dynamic relation to the Hellenic arc and trench system, while part I has its own peculiarity.

Concerning the present deformational pattern, there are new data like:

i ) in situ measurements of the stress f i e l d in no dip dri 1 lings (

BOUKOUVALAS, G . - SABATAKAKIS, N. 1987. Sol1 conditions and bullding damage i n Kalamata from the 1986 e a r t h q u a k e s : Bull. of t he p u b l . works res. c e n t . , V o 1 . 4. 0ct.-Dec. 1467, paq. 267-275 ( I n G r e e k ) .

DEWEY, J.F. & SENGOR, C . A . M . ( 1 9 7 9 ) . Aegean and surrounding regions: cornpiex multiplate and continunn tectonics in a convergent zone. - Bull. geol. Joc. Amer. 9 0 : 84-92: Boulder.

DRAKOPOULOS, J . & DELIBASIS, N., 1982. The f o c a l mechanism of ear thquakes i n the major area of Greece f a r the period 1947-1981. Seismol. Lab. U n i v . A t h e n s . Pub l . 2 , 2 7 p .

FREYBERG, B.Y. (1973) -Geologic des Isthmus von Korinth. Frlanger geol. Abh. H e f t 9 5 ; 183 Seiten.

GALANOPOULOS, A . 1972. Plate tectonics i n the area of Greece, as reflected in the deep focus seismisity. Bull. Geol. Soc. of Greece, IX, 2, 266-285.

GAZETAS, G. 1987. Experience and questions f rom the seismic, enslneerins and geological investigations a t t h e Kalamata town. B u l l . of the p u b l . works Res. c e n t . , Vol. 4, Octo-Dec. 1987, pag. 241-243 (In Greek).

GAZETAS, G. 1988. The role of the ground in t h e Mexican 1985 and Kalamata 1986 earthquakes. lo Z u v k G p ~ o ~ E ~ T E Y V , Hnxav ~ ~ f i q .

GEORGADAS, D. & LAGIOS, E. (1982): Remeasurement of the National Gravity Base Network i n Peloponnesus. - Ann. geol. Pays hellen., 31: 136-145; A t h e n e s .

KELLETAT, D. & SCHRODER, 8. (1975): Vertical displacement of Qua te rna ry shopeline in the Peloponnese (Greece): - S.I.E.S.M., R a p . cornm. int. Mec. Medit., 23/4a: 199-200,

KELLETAT, D., KOWALCZYX, F., SCHRODER, 8 . . WINTER, K.P. 11978): Neotectonics i n t h e Pelo~annesian Coastal R e g i o n s . I n : CLOSS, H. et a l . IEds) : A l p s , Apeninnes, Hellenides: 512-518.

LAJ. G., JAMET, M., SOREL, D., & VALENIX, S.R., 1982. First pale tomagnetic results f r o m Miopliocene series of the Hellenic sedimentary a r c . Tectonophysics, 8 6 , 45-6 .? .

LE PICHON, X . 6 ANGELIER, J. 1979. The Hellenic Arc and Trench sys tem: a key to t h e n e o t e c t o n i c evolution of t h e E a s t e r n Medi t e r r enean a rea . Tectonophysics 6 0 . 1-42.

LE PICHON et a l , 1979. From subduction t o transform motion. A seabeam s u r v e y of the hellenic trench system. Earth & P l a n . Sc. Let., 44, 441-450.

LE PICHON, X. & ANGELIER, 3. 1981. The Aegean Sea P h i l . Trans. R. Soc. London, A 300, 357-372.

MAR1 OLAKOS , I . (1974) : Comparative geomorphological observations between t h e drainage p a t t e r n s of Erymanthos and Ladon (Peloponnesus, Greece). - Prakt. Acad . Athens , 4 9 : 2 3 8 - 2 5 0 .

MAPIORAKOI, H., 1976. IK~WELS Kat a n d y ~ ~ q ~ n i o p ~ u v & v o v npoBAnpdtwv T r ~ w A o 3 Lac K ~ L TEKTOV LKOS TT)c W~Aonovvfiaou. A n n . Geol. Pays Helen., 2 7 , 215-313.

MARIOLAKOS, I . , LZKKAS, S . & PAPANIKOLAOU, D. ( 1 9 7 6 1 : Q u a n t i t a t i v e geomorphological analysis of drainage p a t t e r n s i n t h e Vth order basins of A l f i f i s Rlver (Pe loponnesus . Greece. - Ann. geo 1 . Pays he 1 l e n . . 3 0 . 2 : 441-454, A t h e n e s .

MARIOLAKOS, I . 6 PAPANIKOLAOU, D. ( 1 9 8 1 a ) : The i n f l u e n c e of t h e map s c a l e on t h e results of the quantitative geomorphological analysis exemplified by A l f i o s River (Peloponnesus, Greece. - Ann. geol . Pays he 1 len. , 30, 2 : 441-454, Athenes.

MARIOLAKOS, I . & PAPANIKOLAOU. D. (1981b): The Neogene Basins of the Aegean A r c from the paleogeographic and the geodynamic point of view. - Proc. int. Symp. Hellenic Arc and Trench, Athens 1981: 383-399.

MARIOLAKOS, I . , SYMEONTDIS, N. , LEKKAS, S. . KAROTSIERIS, 2 . & SIDERIS, CH. (1981a) : The deformation of t h e area around t h e e a s t e r n Corinthian Gulf affected by t h e ear thquakes of F e b r u a r y to March 1981. - Prac. i n t . Symp., Hellenic Arc and Trench, Athens 1981: 400-420.

MARIOLAKOS, I . , PAPANIKOLAOU, D. (1985): Deformation pattern and relation between deformation and seismicity i n t h e Hellenic arc. - Bull. geol. Sac. Greece, 19: Athens. (in press) .

MARIOLAKOS. I . , PAPANIKOLAOU. . & LAGLOS, E. ( 1 9 8 5 ) . h neotectonic geodynamic model of Peluponnesus based on morphotectonics, repeated gravity measurements and seismicity. Geol. Jb., 3-50 , 3-17.

MARIOLAKOS, I & PAPANIKOLAOU, D. Deformation p a t t e r n and relation between deformation and seismicity i n t h e H e 1 lenic A r c . (1987) .

MARIOLAKOS, I , . SABOT. E . , LOGOS, E., LOZIOS, S . , MERTZANIS, A . , FOUNTOULIS, 3 . 1987. The Geographical distribution of the rockfalls caused by the ear thquakes of Kalamata. 1st Geogr . Congr . , Athens 1987, Abstracts ( i n Greek) .

MARIOLAKOS, I . , SABOT, V., LOZIOS, S . , LOGOS, E., FOtTNTOULIS, 3. 1987. Morphotectonic observations at t h e graben of the Dimiova-Perivolakia area, 1st Cons. of the G e o g r . Soc . of Greece. Athens 1987, Abstracts. { I n G r e e k ) .

MARIOLAKOS, I . , LOGOS, E . , LOZIOS, S . , FOUNTOULIS, J. 1988. Neotectonic deformation of the Zimbeli Fault sur face teas t of Kalamata t o w n ) . 4th Congr . of t h e Geol . Soc. of Greece. , Athens May 1988, Abstracts ( i n Greek) .

MARIOLAKOS, I . , FOUNTOULIS, J. , LOGOS, E . , LOZIOS, S. 1989. Surf ace f a u l t i n s caused by t h e Kal arnat a-Greece ea r t hquakes ( 1 3 . 9 . 8 6 ) . Tectonophysics, Vol. . . . . . . 1989.

McKENZIE, D . P . 1970. P l a t e tectonics i n the Mediterranean Region. N a t u r e , 2 2 6 , 239-243.

McKENZIE, D . P . 1972. Active tectonics of t h e Mediterranean Region. Geoph. J.R. astr. s o c . . 3 0 . 109-185.

McKENZIE, D . P . 1978. Active tectonics of the Alpine-Himalayan belt the Aegean sea and surrounding r e g i o n s , Geoph. J . R . a s t r . soc . , 55 ( 1) , 217-2754.

MERCIER, J . L . 1979 . Signification neotectonique de 1 ' A r c Egeen. Une revue des i d e e s . Rev. G e o l . Dyn. Geogr. Phys. 2 1 , 1 5-15.