Active Normal Faulting, Drainage Patterns and Sedimentation in Southwestern Turkey

Journal of the Geological Society, London, Vol. 149, 1992, pp. 1031-1044, 10 figs. Printed in Northern Ireland

Active normal faulting, drainage patterns and sedimentation in southwestern Turkey

STUART PATON Bullard Laboratories, University of Cambridge, Cambridge CB3 OEZ, UK

Abstract: The geomorphology of the rapidly extending area of western Turkey is principally controlled by large active normal faults. The graben formed by the faults are asymmetric and about 10-20 km wide. Measurements of the rotation ofNeogene sediments in the footwall of the active faults and 2-D modelling of gravity data show the extension across each graben to be about 6-10 km, suggesting that the whole region has undergone only small degrees of extension (p = 1.2-1.3). The faults bounding the grabens are segmented on a length scale of 5-10 km with the segments linked by some means other than single 'transfer' faults. Where the footwall lithology is resistant to mechanical weathering, axial drainage is important and rivers cut through the line of the fault at the end of fault segments, producing large fans. Where the footwall lithology is less consolidated, drainage is generally in linear valleys. Major graben can have more than one phase of faulting, with the main graben bounding fault stepping successively into the hanging wall.

Western Turkey (Fig. 1) is part of a zone of distributed exten- 27 E 30, E sional deformation whichincludes the Aegean Sea, Greece, Yugoslavia, Bulgaria and Albania. Itis one of the most rapidly extending areas on the continents and, as such, has high seismicity and a landscapewhich is controlled to a large degree by

theactive normalfaulting. This paper examines the rela- -39 N tionshipbetween faulting, geomorphology and drainage in southwestern Turkey, following a similar method to that used by Roberts & Jackson (1991) in their recent study of central Greece. These relationships, which have a major control on sedimentation patterns, are more easily studied in active areas rather than in ancient extensional basins like the North Sea. -38N The observations and generalizationsmade here should, however, be applicable to olderbasins. Therotation ofsedi- mentary beds in the footwall blocks of faults and gravity data are alsoused to constrain amount of extension across the area. The north-south rate of extension across the whole region (i.e. between Crete andBulgaria) has been estimated at between

4C60mm a-' (McKenzie 1978; Le Pichon & Angelier 1979; -37 N Jackson & McKenzie 1988). Studies of recent seismicity suggest that most of the extension is achieved on large faults during earthquakes of magnitude 6.0 orgreater, and that smaller earthquakes and aseismic creep play only a minor role in the Fig. 1. Location map of western Turkey showing major normal regional deformation of the upper crust (Jackson& McKenzie faults (thick lines) with ticks on downthrown sides. The graben 1988). Fault plane solutionsof major earthquakes (Jackson& referred to in this paper are the Gediz graben, the Buyiik Menderes White 1989) and accurate microearthquakestudies (Soufleriset and the Gulf of Kerme. al. 1982; King et al. 1985; Hatzfeld et al. 1987; Lyon-Caen et al. 1988) in the Aegean area show the seismogenic layer of the crust to be about 1C15 km thick. Faults with along strike length of about 10 km and which extend to a depth of about 10 km, will tation of palaeomagnetic data (Kissel & Laj 1988) suggest that produce approximately magnitude 6.0 earthquakes. Thus it is most of the extension has occurred in the last 5 Ma. In western the large faults of these dimensionsthat areof interestin under- Turkeythere waswidespread deposition of Miocene con- standing the kinematics of the area. It is also faults of this tinentalsediments but localiseddeposition within grabens dimension that will be most easily observed in older basins does not appear to have developed until the Pliocene (Stein- from seismic profiles. Smaller faults and smaller earthquakes inger et al. 1985). generally occur away from the large faults and probably rep- The geomorphology of western Turkey is dominated by a resentinternal deformation of theblocks bounded by the series of approximately E-W-trending graben (Fig. 1). In some major faults. cases these are wholly onshore while elsewhere the hanging Extensionin the Aegean area is thought to have started wall is now underwater. Although the precise kinematics of sometime in themiddle Miocene (Mercier et al. 1979, 1987, each graben maybe different, the way the faults are segmented, 1989) related to developmentof the Hellenic arc. However the effect of this on the geomorphology and the drainage, and seismic evidence (Jackson & McKenzie 1988) and an interpre- the effect of a rotating footwall will be broadly similar and 1031

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 1032 S. PATON

28'E 28'15 28'E

Fig. 2. Faulting along the Gediz graben. Main faults are shown in thick lines with solid ticks on downthrown side; minor faults are in thinner lines with open ticks on downthrown side. Arrows show fault movements at these locations, from earthquake fault plane-solutions or slickenlines, with the dip of the fault given. The 200m contour is shown and land over 1OOOm is stippled. Dash-dot lines I, 2 and 3 are the gravity transects shown on Figs 6, 7 and 8 respectively

thus general principles can be developed. The area has been bounded by a normal fault system, part of which moved in a studiedusing satellite images, topographic and geological major earthquakein 1969, near AlaSehir (Eyidogan & Jackson maps and fieldwork. 1985). Faults along the graben were studiedusing Landsat Three areas in particular will be considered in this paper Thematic Mapper satellite images together with field mapping (Fig. 1). The Gediz andBiiyiik Menderes graben are two of the in the context of a review by Saroglu et al. (1987) who carried major onshore graben in western Turkey while the Gulf of out a general study of faulting in the whole of western Turkey Kerme, which is bounded on the northside by a normal fault,is using aerial photographs and fieldwork. Their study was used now underwater. In each case, the continuity of the faulting as a basis for the general nature of the faulting in the graben. along strike, and the effect of the faulting and footwall litho- Many of the faults bounding the floor of the graben (Fig. 2) logy on drainage patterns and sedimentation patterns are de- show up as clear scarps and truncated spurs on the Landsat scribed and compared. The lithologies in the footwall of the images and these can thenbe traced on the ground andchecked main faults are describedbriefly and the rotationof these sedi- for fault breccias or other featuresof faulting. Unfortunately, ments is used to estimate amountsof extension. The amountof becausethe main active faults generally cut poorly con- extension estimated from sediment rotation is compared with solidated Neogene sediments (Steiningeret al. 1985) (Figs 3b & that calculated fromgravity modelling of the thicknessof sedi- 4b),the actual fault planes were not observed in the field ments in the grabens. because they are degraded or covered by fan deposits. On the other hand, older, probably inactive faults which place Neo- gene sediments againstmetamorphic basement do notshow up Satellite images as well on the satellite images but, in the field, brecciated zones Landsat 5 Thematic Mapper tapes were processed using an 12S system are observed. These faults also showup as a step on thehillside at the NERC facility at Monks Wood. A scene from the late autumn which can be seen on the ground or on a topographic map and was used as this time of year provides a low sun angle which enhances can thus be traced more easily in the field. the topographic contrasts, is after the hazy summer period, and is The preciseage relationship between the two lines of before there is snow on the hills. The data was contrast-stretched and faulting on the southside of thegraben is difficult to determine. edge enhancement was carried out. Various combinations of bands The Neogene sediments which were deposited to the north of were used to try to pick out different features. A combination of bands the southernmost fault are now being uplifted and backtilted 4,5,3 for red, green and blue respectively was most widely used as this (Figs 3b & 4b). Therefore, the sequence of eventsis either that clearly showed the faults and differentiated deposits in the valleys. the southern fault is now inactive and the northern fault is active, or that both faults have been active throughout the Faulting along the Gediz Graben history of the graben but originally the southern fault was more active and now the northern faultis more active. In either The Gedizvalley (Figs 1 & 2) is one of the major E-W-trending case, the northern fault nowtakes up the major motion andit is graben inwestern Turkey.It is about150km long and is this fault which at present controls the landscape.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 TECTONICS AND SEDIMENTATION, SW TURKEY 1033

I N 1

U Fluvial Neogene Quaternary Fans :::.:: Pre-Neogene

As there is a large thickness of Neogene graben sediments in central Greece (Jackson et al. 1982; Roberts & Jackson between the two faults, the southern faultsystem (which places 1991) but the reason for this stepping is not well understood. Neogenesediments against basement) must have been the To the south of Turgutlu (Fig.4b), three sets of north dip- important faultin the past. Thus, the motionis now being taken ping faults are observed.As the sedimentsare all non-marine it up on faultswhich are in the hangingwall of the original major is not possible to date them, but the more friable nature and fault. Stepping of faults into the hanging wall block has been generally lower dips of the Turgutlu formation (Fig.4b), com- seen in sand box models (McClay & Ellis 1987) and has also pared with the Neogene sequence, suggests that the Turgutlu been observed in the Basin and Range when faults rotate to a formation may be younger than the Neogene sequence. The hwangle (Proffet 1977). The same situation is observed along observation that the Turgutlu formation, which was deposited the Biiyiik Menderes grabenin western Turkey (see below) and in a graben, is now being uplifted relative to the valley floor

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 1034 S. PATON

Fluvial Turgutlu Formation Quaternary 0 10km ,I#,,, Fan8 bogme

(a) (b) 0 Re-Nogene

Fig. 4. (a) Map of western area of Fig. 2. Symbols as in Fig. 3a. (b) Geology of area shown in (a). Symbols as in Fig. 3b.

and tilted by the most northerly fault set, suggests that this only situations where there are clearoffsets in the fault or clear fault set is the most active at present. The processof the major changes in the strike of the fault are consideredbe to the end of fault stepping into the hangingwall, towards the centre of the a fault segment. In many cases (e.g. 1 km south of Turgutlu) a graben, has thus taken place twice in this area. The area near river cuts the line of the fault, but this is considered to be Turgutlu is particularly complex as the fault system bifurcates erosional and not the end of a fault segment. The fault seg- to the west. ments are not joined by a single ‘transfer’ fault. Roberts & Although, in general, the main active fault places young Jackson (1991) describedsimilar segmentation in Central alluvium against Neogene sediments, to the south and east of Greece but the faults in western Turkey seem to be segmented Manisa (Fig. 4b) the young alluvium is faulted against Meso- on aneven shorter length scale.In Greece many of the footwall zoic limestone with a polished, brecciated surface being pro- blocks are well consolidated,coherent Mesozoic limestone duced (see also Allen 1975). The limestone provides the ideal which is resistant to mechanical erosion which contrasts with situation for development of fault plane surfaces with breccias thepoorly consolidated, friable Neogene sediments in the and slickenlines as well as showing up clearly on the satellite Gediz graben. In general the older inactive faults, which have images, and is also one of the few places where a good estimate MenderesMassif metamorphic basement as theirfootwall of the fault dip can be made (see below). lithology, are longer. More importantly,where the active fault Although there is faulting along the whole length of the has pre-Neogene lithologies in the footwall, as near Manisa, graben (Figs 2, 3 & 4), the faults are discontinuous on the scale the segments are generally longer. This segmentation appears of a few kilometreswith no individualsection longer than to be a ubiquitous feature of normal faulting observed, for 10 km and most only 2-5 km long. Segmentation on faults in example, in Greece (Roberts & Jackson 1991), the Basin and western Turkey also occurs on a smaller scale of tens to hun- Range (De Polo et al. 1991) and the Suez rift (Garfunkel & dreds of metres (Hancock & Barka 1987; Stewart & Hancock Bartov 1977). It is important incontrolling drainageand 1991) but these smaller-scale features will not be as important deposition patterns, as discussed below. in controlling drainage and sedimentation as the kilometre- The north side of the Gediz valley is also fault-bounded scale features. The kilometre-scale segmentation occurs as the along much of its length (Figs 2, 3a & 4a). However, the fault displacement changes from one fault to another andis accom- scarps are much less distinct, the topography is much more modated either by a change in the trend of the fault or by the subdued and thereis a lack of recorded seismic activityon the fault continuing on a similar parallel trend offset by between north side of the valley. The faults on the north side are anti- lOOm and 1 km. As the faults cannot be traced in alluvium, thetic to the main fault system along the south side of the

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 T ECT ON ICS AND SEDIMENTATION,TECTONICS AND SW TURKEY 1035

graben, in the sense that the faults on the south side control thewell-polished surface of recemented brecciated limestone were topography and asymmetry of the graben. Nonetheless, these measured, and give an approximately pure dipslip fault, with faults are also segmented over distances of less than 10 km. average slip vector,which stays approximately constant, about The Gediz grabenis thus similar to the Gulf of Corinth, centralnortheast and dip about 55" (Fig. 2). The fault surface, how- Greece, in that there is no change in polarity of the major fault ever, shows marked change in strike and dip overa distance of along the graben, butdiffers from the Gulf ofEvvia where the about 1 km; therefore, although the slickenlines show the fault polarity does change (Roberts & Jackson 1991). to be dominantly dip-slip, locally there is a significant compo- The graben becomes generally narrower towards the east nent of strike-slip. and the valley floor rises gradually. These features are consis- The dip of the faults therefore varies quite markedly along tentwith the overall structure of western Turkey which the length of the graben. The present dip will depend on the suggests that the greatest stretchingis towards the west and so original dip of the fault, the amountof rotation and the number the eastern end of the graben is probably relatively poorly of generationsof faulting, i.e. the effects of fault migration into developed. The variation in amount of stretching along the the hanging wall, will also be important.Therefore, there may graben can be taken up by having increasing amount of throw not be a simple relationship between the observed fault dip and on the faults to the west compared with the faults to the east. the amount of extension accommodated by a single fault. Structural features at a high angle to the main strike of the graben, are observed on the north sideof the valley (Figs 2 & 3a). About 5 km eastof Adala thereis a clear normal fault with Drainage a SW-NE trend, while many lineaments are also observed on Drainage in thefootwall of the faults is mainly in distinct thesatellite images. Bunbury (pers. comm.)has described linear valleys which drain small basins in the high mountains features of this orientation in the Kula area (Fig. l), while a to the south of the graben (Figs. 3a & 4a). The valleys incise magnitude 6 earthquake at Demirci in 1905 (Ambraseys 1988) deeply and cut far south into the mountains with the drainage and minor seismic events north of the graben towards Simav divide being about15 km south of the graben-bounding faults. also lie along a similar SW-NE trend (Sengor 1987). Sengor The drainage divide being so far south is unexpected as the (1987) suggested that these were cross faults due to differential effect of footwall uplift would beto have the divide just south stretching of the hanging wall above low angle detachments. of the graben and the majorrivers flowing southward down the More distinct cross-structures are present on the south side of dip slope of the tilted fault block. The Neogene sediments in the Buyuk Menderes asis discussed below. Whatever their pre- the footwall also have many deep gullies showing rapid and cise cause,the cross-structures are important in controlling active uplift with intense erosion of the poorly consolidated local deposition patterns. sediments.The drainage pattern therefore appears to be strongly affected by thepresence of friable, poorly con- Surface faulting solidated Neogene sediments in the footwall that are easily eroded and so can be cut back into. Although some clear fault scarps are observed in the field, the Although the drainage divideis about 15 km to the south of nature of the faultingis best inferred from earthquakes. A M, the northernmost graben-bounding fault, the divide is much 6.5 earthquake at Alagehir in 1969 caused widespread damage closer to the southern faults which have metamorphic base- (Eyidogan & Jackson 1985). Analysis of the waveform of this ment in their footwall (Figs 3a & 4a). The nature of the foot- event shows that the fault dipped NNE at30-35" and involved wall lithology is therefore important in controlling the pos- almost pure normal slip, to a depth of about 10 km (Fig. 2). ition of the drainage divide. Arpat & Bingol (1969) and Allen (1975) describe surface Some of the largerivers enter the graben at the endsof fault ruptures from the 1969 Alagehir earthquake. Arpat & Bingol segments. Theriver 5 km to the southwest of Turgutlu (Fig. 4a) (1969) mapped several ruptures on bothsides of the valley but enters the grabenwhere there is a change in strike of the fault, it is not clear from their description which is the actual fault and the river 3 km to the southwest of Salihli (Fig. 3a) enters break andwhich ruptures are justslumping associated with the the graben where there is an offset in the fault of about 0.5 km. earthquake. The amount of displacement they describe and the However, other rivers cut across theline of the fault. The river direction of throw is very variable suggesting that many of the 1 km east of Kemalpaga (Fig. 4a) and the major river in the featuresare just slumping, as suggested by Ambraseys & southeast of the area coveredby Fig. 3a both cut theline of the Tchalenko (1972). Thetwo most likely faultbreaks, which fault. In the cases where the rivers cut the line of the fault, the approximately coincide witha fault mapped during the present fault segments continue along strike and are covered by al- work, were located just to the southwest of Alagehir (Fig. 2) luvium. Thesituation observed here is very different from and are about5 km long. Allen(1975) describes the faulting as where the footwall is of a more resistant lithology, as in the 'extending discontinuously at least 30 km from Hacialiler on Gulf of Kerme (see below). the east to Yenikoy on the west', i.e 15 km either side of Al- The Kemalpaga river (Fig. 4a) enters the graben west of agehir, but gives no description of the nature of the rupturesor Turgutlu and flows north-west to join the Gediz river. Where their continuity and only shows the extentof the faulting ona the Kemalpaga River cuts through the fault it is flowing 'up- small scale satellite image. Unfortunately, therefore, it is not slope' i.e. the general topographic dip is southwards but the clear how the1969 event relates to the faulting shownin Fig. 2. river is flowing northwards. The river must predate the tilting About 5 km east of Manisa (Fig. 4a) there is a very well due to faultingin this area. Rivers predating faulting may con- exposed fault surface with surface area of c. 2000 m'. Allen tinue on a similar course as long as the downcuttingof the river (1975) alsoshows this fault and describes a faultscarp in keeps pace with the uplift on the fault. If footwall uplift is terrace gravels2 km to thewest of the fault surface. The faultin particularly rapid, then the downcutting of the river may not the gravels is about lOOm into the hangingwall of the main keep pace with the uplift and so the course of the river will be break in slope and shows that the actual line of the fault may reversed. The Kemalpaga river also flows round the south side be covered by young alluvium. The major slickenlines on the of the limestone area to the south of Manisa, and only cuts

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 1036 S. PATON

through to the main grabenwhere the footwall lithology is the fluvial deposits. The fan deposits are sourced from the higher more friable Turgutlu formation. hills in the footwall to the south and are brought down by The Gediz andAlaSehir rivers which flow westwards along rivers. The many gullies cut into the lowerhills suggest that in the floor of the main graben (Figs3a & 4a) aregenerally on the times of flood there is intense erosion and rapid deposition of north side of thevalley. The rivers are thus on the opposite side the sands andgravels. Some of the rivers have also moved large of the valley from the main graben-bounding fault. This is the boulders (> 1 m) and poorly consolidated conglomerates are reverse of the situation observed in the Basin and Range pro- developed. The fans,which are mainly inactive, slope towards vince of the western United States (Russel 1895; Gilbert 1926; the north at a few degrees and extend several kilometres into Leeder & Alexander 1987) and that expected from a ‘trap- the valley floor. As described above, the fans tendto divert the door’-type graben with thevalley floor tilted towards the main course of the Gediz river northwards. fault. Annual precipitationis much greaterin the Gediz graben The main valley floor is very flat and, where drainage chan- than the Basin and Range (510mm at Aydin compared with nels are present, the sediments areseen to be fine sands orsilts 160mm at Reno, Nevada; MeteorologicalOffice 1958), and, as with lacustrine limestones in places. much of this rainfall is during the winter months and there is acute overgrazing, erosion is very severe in western Turkey. Southern margin of the Gediz graben. The Neogene sequenceon Therefore, the major control on the slope of the graben flooris the southside of the graben consistsof alluvial sandstones and fans coming off the fault scarp, which build out across the conglomerates (Figs 3b, 4b). The sequence has a maximum valley floor tending to push the river away from the fault to- thickness of about 750 m. Distinct channels are present within wards the opposite side of the graben. The situation is quite the sequence which shows rapid lateral variations in lithology different from that observedat Acigol, east of Denizli (Fig. l), and unit thickness. Large conglomeratic clasts (up to 50cm) where the lake is locatedalmost against the southern fault and poor sorting suggest proximity to source. The clasts are bounded margin of the basin. At Acigol there is little develop- predominantly of metamorphic and quartzitic origin suggest- ment of alluvial fans andso the basin is tilted towards the main ing erosion from the MenderesMassif basement, to the south. basin bounding fault. A major influence on fan deposition is Rare limestone clasts are similar to limestones seen in a thick therefore footwall lithology: where it is resistant to erosion Mesozoic sequence which occurs to the southof Manisa uplif- (e.g. Acigol and near Manisa) there is little fan development, ted in the footwallof the fault.Limestone is also found against whereas where it is less consolidated sediment (as along most the fault at Alavehir (Fig. 2) and may have been preserved as a of the Gediz graben) major fans are produced. sliver alongthe fault. Limestonemay have been deposited above the metamorphic rocks over much of the area but has Sediments along the Gediz graben since been eroded, making estimates of the throw on the fault difficult. Poorly cemented white limestone of different charac- TheGediz graben provides a useful areafor studying the ter is found on the northside of the graben and is discussed in amount of rotation of sediments due to footwall-block rota- more detail below. tion about a horizontal axis. Therotation is related to the About 2 km south of Derekoy (Fig. 2) the sediments are amount of extension in the area and so measurement of sedi- notable for the large thickness of conglomerate exposed in a ment dips with known original orientation and the dip of the distinctive gorgeabout 100 mdeep in the footwall of the north- fault also known, can lead to an estimateof crustal extension, ern fault. The conglomerate hcs clasts up50 cmto in size which p. Sediment dips were measured along much of the length of vary from sub-rounded to sub-angular,suggesting proximity to the graben and the lithologies studied. Sediments which were source, and have large scale (> 10m) cross bedding features. depositedapproximately on an horizontal surface, such as These conglomerates are probably a large fan deposit similar limestones, mark or fine sandstones, are studied in preference to those of thepresent-day active graben. The Neogene to sediments, such as conglomerates, which may have had a sequence on the south side of the Gediz graben was clearly steep original dip. deposited in a graben and has since been uplifted by the main As the sediments are continental it is difficult to correlate active normal fault that forms the distinctive break in topo- between different sections along the graben. Liittig & Steffens graphy on the south side of the valley. (1976) suggest that significant graben type depositionbegan in To the south of Turgutlu there are three, rather than just the Gediz graben from Tortonianto Messinian (< 12 Ma) and two, sets of faults (Fig. 4b). The faultset that is inferred to be is continuing to the present day. The stratigraphy hasreceived relatively little attention(Becker-Platten 1970; Benda et al. the youngest separates the present graben floor from poorly 1977) and, due to the continental nature of the sediments, the consolidated sediments which are probably Plio-Quaternary establishedsequence is based on lithologicalrather than (the Turgutlu formation). The deposits south of the middle fault set are similar to those described above and thus represent palaeontologicaland radiometric controls. For this reason, generallithological patterns are described here without fans and channels. The Turgutlu formation deposits are finer attempting to correlate sequences along the graben. grained than the Neogene sediments, with more silt and mud The sedimentary sequences from three areas are described. lithologiesbut similar metamorphic clasts. The lithological The present graben floor sediments are related to the active differences between theolder Neogene sediments and the processescontrolled by normalfaulting, and the Neogene Turgutlu formation reflect the differences in their dominant sediments on the north and south of thevalley are shown to be source areas. The olderNeogene rocks are derived mainly from graben sediments now being uplifted relative to the present thehigh basement metamorphic rocks tothe south. The graben floor. The thickness of the Neogene sequence is also Turgutlu formation sediments are sourced from the Neogene comparedwith the thickness determined from gravity sediments, which are friable, less well consolidated and hence modelling. more easily eroded and produce finer grained sediments.

Present grabenfloor. The present graben flooris dominated by Northern margin of the Gediz graben. The Neogene sedimentson twofeatures: fan deposits along the southern margin, and the north sideof the graben are either separated from the graben

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 TE CTO NICS AND SEDIMENTATION.TECTONICS AND SW TURKEY 1037

floor deposits by minor south-dipping faults (e.g. south and The faulting along the grabenis discontinuous on ascale of east of Adala, Fig. 3b) or are unconformably overlain by the generally 2-5 km and no individual segment is longer than graben floor deposits (e.g. north of Kemalpava, Fig. 4b). The 10 km. As with the Gedizgraben, thesegments are identified by Neogenedeposits are lacustrine limestones (to the west of a change in strike of the fault rather than clear en-echelon Adala) or finer grained sandstones and siltstones (to the north segmentation as observed on some of the grabens in central of Kemalpava).There is littleindication of distinct fan- or Greece (Roberts & Jackson 1991). Along the full length of the channel-deposits. The observedclastic sediments areinter- graben the major faultis south dipping and thereis no change pretedas distally deposited riveralluvium. The limestones in polarity. may have formed in small lakes that developed in the early As observed in the Gediz graben, along much of the length stagesof graben formation but were later filled in by high of thevalley the northside isbounded by two sets of south-dip- proportions of clastic input. ping faults (Fig. 5a). The southern set of faults bounds the present valley floor and runs along thebase of the topographic escarpment on the north side of the Buyiik Menderes valley, Sediment dips placing young fan and fluvial deposits against Neogene sediments. The northern fault set places the Neogene sediments In theNeogene sediments along the southside ofthe graben the against metamorphic basement rock of the Menderes Massif. sediment dips are very consistent (Figs 3b& 4b) andin general As theNeogene sediments, which are grabenrelated (see are about1C15" to the south. Southis the senseof dip expected below), are uplifted relative to the present valley floor, it is for rotation in the footwall of a north dipping normal fault. In likely that, as with the faults in the Gediz graben, the north- places the dipsare greater or are more variablein strike butthis ernmost fault is largely inactive with the southern fault now variability is due to proximity to one of the major faults or being the important active fault. In places, such as 10 km east other smaller faults. of Nazilli, there is only one fault present, and here the present In the Turgutlu formation (Fig. 4b), the dips are generally valley floor is directly faulted against the basement. This situ- lower than in the older Neogene sediments. Lower dips are to ation is analogous to that to the southeast of Manisa in the be expected as the sedimentsdo notrecord sucha long periodof Gediz graben (Fig.4a & b). To the west of Aydin, there are also rotation due to faulting. The dip of the Turgutlu formation north dipping faults which have upfaulted metamorphic base- sediments is southor southwest which is away fromthe ment into the Neogene basin (Fig. 5a & b). These faults are Manisa-Turgutlu branch of the bifurcating fault system in that antithetic to the major faultsto the north andwould have been area (Fig. 4b). intrabasinal faults during the deposition of the Neogene sedi- The dips along the north side of the graben are more vari- ments. able and, in general, are less than those along the south side. The south side of the valley is also bounded by faults over The dips areusually only 5-6" and are orientatedin a variety of muchof its length. However, these faults have much more directions apparently not related to faulting. The lower dips subdued topographic scarps thanthose along the northside of may be because the bedsare younger and so have not rotated as the graben, and are analogous to the faultsalong the north side much or because the area is not acting as a competent hang- of the Gediz graben. ingwall block. These sediments sit in the footwall of the south Three main valleys join the south side of the Buyuk Men- dipping fault on the northside of thegraben, butin the hanging deres graben (Fig. sa). Two of these, the Karacasu and Boz- wall of the main graben bounding fault,so a complex picture is dogan valleys, appear to be bounded by normal faults. The to be expected. directionof tilting observed in the Neogenesediments, the development of alluvial fans (now largely inactive), the mor- Faulting along the Biiyiik Menderes graben phologyof the range-fronts (in the field andon Landsat images) and historical seismicity studies (e.g. Ambraseys 1971) The valley of the Biiyuk Menderes river (Figs 1 and 5a), like suggest that the valleys are bounded on their west sides by that of the Gediz, is one of the major E-W-trending graben in large, east dipping normal faults. Thewesternmost graben, the western Turkey. The structure of the Buyiik Menderes is also Cine basin, is also fault bounded along both sidesof the valley very like that of the Gediz graben in that it is about 150 km (Fig. 5a). long, about 10-20 km wide, is bounded by a normal fault sys- The Karacasu and Bozdogan graben are notable for their tem which has broken along someof its length in recent earth- structural similarity; both graben are about I0 km wide, about quakes and, along some of the graben, there are two sets of 30 km long and have similar sedimentary fills. The main faults faults. Many of the features observed in the Gediz graben are also have similar surface traces.In the north partof each basin, also present in the Biiyiik Menderes and so they will only be the main graben bounding fault trends approximately north- discussed briefly here. The main differences between the two south but about20 km southof their intersection with the floor graben are that the main fault bounding the Biiyuk Menderes of the Buyiik Menderes graben, the faults both change direc- graben is on the north side of the valley whereas that in the tion to trend NW-SE. Gediz graben is on the southside, and thatthe Buyuk Menderes Thedrainage patterns observed in theBuyuk Menderes has distinct subsidiary graben which join the main valley. The graben aresimilar to that observed in the Gediz graben. To the subsidiary valleys are the 'cross-graben' of Sengor (1987). This north of the Buyiik Menderes graben linear drainage basins are paper will consider only the central section of the Biiyuk Men- actively eroding into the uplifted Neogene sediments. Some of deres, fromOrtaklar in the west toCubukdag in theeast the rivers enter thegraben floor at the endof fault segments but (Fig. 5a). To the west of Ortaklar the graben changes trend to this is by no means generally the case, e.g. west of Aydin. The NE-SW and becomes more complex. To the eastof Cubukdag Biiyuk Menderes river, which flows westwards along the main the valley becomes less distinct for a distance of about 20 km, graben, is generally on the south side of the valley due to the before becoming more distinct again farther east, near Sarakoy presence of large fans being produced from the high topo- (Fig. l), where the fault changes polarity to north dipping. graphy to the north of the graben. The location of the Biiyiik

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 1038 S. PATON

Fig. 5. (a) Map of main section of Biiyuk Menderes graben, with symbols as in Fig. 3a. The dashed line X-Y is the transect of the gravity model shown in Fig. 9. (b) Geology of area shown in (a). Symbols as in Fig. 3b.

Menderes river is apparently controlled by the same factors these events were calculated assuming a nucleation depth of that influencethe position of the main riversin the Gediz 50 km but a morerealistic depth of 10 km produces resultsvery graben. similar to the old ones e.g. Eyidogan & Jackson (1985) and Jackson (unpublished data). The data for the 1955 Soke earth- Surface faulting quakeare old andnot reliable. The available first motion polarities are consistent with oblique left-lateral and normal Unlikethe Gediz graben,there havebeen no major earth- slip on a fault striking 055", which is the local strike of the quakes in the Buyuk Menderes graben since good instrumental SE-dippingfault along the NW margin of thispart of the records began about 50 years ago. The nearest events are the Buyuk Menderes graben, and dipping about 50" SE. The slip 1955 Soke-Balat earthquake (M, = 6.8) tothe west ofthe vector is in the direction 024", but this mechanism is not of graben, and the1965 Denizli earthquake (mb= 5.3)to the east good quality (McKenzie 1972). The mechanism of the Denizli (McKenzie 1972, 1978). McKenzie's fault plane solutions for earthquake is consistent with pure dip slipon a faultdipping at

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 TECTONICS AND SEDIMENTATION, SW TURKEY 1039

c. 20" and with a slipvector of c. 010" (McKenzie 1972), Sediments along the margins of the Biiyiik Menderes although thiswas a smallevent and so itsmechanism is graben poorly constrained. Althoughthere havebeen nomajor eventsrecorded in- As with the Gediz graben, the depositsin the Biiyiik Menderes grabenare non-marine and so theestablished stratigraphy strumentallyin the main part of the Biiyiik Menderes (Becker-Platten 1970; Benda et al. 1977) is based on litho- graben, a large earthquake occurred in the graben on the 20 logical ratherthan paleontological or radiometriccontrols. September 1899 (Allen 1975; Ambraseys 1971, 1988). The The sequence observed in the Biiyuk Menderes is very similar area of maximum destruction was along the north side of the to that seen in the Gediz graben and so will only be described graben stretching from Nazilli (Fig. 5a) in the west to Den- briefly here. A more complete description is given in Roberts izli (Fig. 1) in theeast. Relatively little damage wasre- (1 988). ported from the south side of the graben although this was Along themain valley of the Buyiik Menderes, the Neogene (Schafer 1900), and stillis, relatively sparsely populated sequence is well exposed on the northside of thegraben where compared with the north side of the graben. From the area it is being uplifted in the footwall of the major faults (Fig. 5b). overwhich the shock wasfelt, Ambraseys & Finkel (1987) The lowestunits in thesequence are well-cemented con- estimatedthat the earthquake was M, c. 6.5 0.2.Follow- glomerates unconformably overlain by aseries of well-lith- ingthe mainshock, the area continued to suffer from ified lacustrine and fluvial sandstones, claystones, thin mark aftershocksfor about the following six months (Schafer 1900). Contemporarydescriptions e.g.Schafer (1900), men- and minor lignites. The lignites have been dated as Miocene in tion widespread ground cracks trending approximately east- age on the basis of their sporomorph content (H. Karaman- deressi pers. comm.). These units are strongly deformed and west along the north side of the graben. One of the cracks have a thickness of about 300m. followedthe topographic scarp along the north sideof the The above units are overlain by a sequence of poorly lith- valley for over 6 km with vertical displacements of between ified, mainly fluvial, conglomerates, silts, sands and clays. The 1.5 and 2m down to the south. The length and location of units dip at between 10-25" north with numerous intraforma- the crack suggests that it is likely to have been part of the tional unconformities. Clasts in the conglomerates are base- main fault break at the surface and not a superficial feature. mentlimestone and schists andare 40cm in diameter. This crack is not observable now; Schafer (1900) noted that < Palaeocurrent directions are N-S, E-W and W-E consistent within one yearof the earthquake almostall trace of the with the present-day drainage. Minor lignite horizons occur ground break haddisappeared. Allen (1975), talking to throughout the sequence, which is relatively unfossiliferous, elderly villagers who remembered the 1899 earthquake, sug- with rare fossils of Planorbis sp. The total thickness of the unit gested that the fault break extended from Umurlu (Fig. 5a) is up to 2 km butin some partsof the basinis 300 m. This unit in the west to Sarakoy (Fig. 1) in the east, a total distance of < is in turn unconformably overlain by up to 300m of poorly over 70 km. consolidated alluvialconglomerates with minor clays and The 1899 earthquake was observed in poorly consolidated sands. On the basis of lithology and stratigraphical position, conglomeratesand recentalluvial deposits and so thedis- the fluvial conglomerate sequence is thought to be Pliocene- placement across the fault break may be exaggerated by up to Quaternary in age and the alluvial sequence has been similarly two times, as at Borah Peak (Riching et al. 1987) and along dated as Quaternary (H. Karamanderessi pers. comm.). The Recent normal fault scarps in Tibet (e.g. Armijo et al. 1986). Neogene to Quaternary sequence was clearly deposited in a The true coseismic displacement in the 1899 event is, there- graben. fore, probably about 1.0m and so the break is likely to have The sediments in the three crossgraben (the Cine, Karacasu been10-20 kmlong (assuming that DIL wasbetween 1 X and Bozdogan basins) are similar to the sequence seen in the lO-' and 1 X 10-4; see Scholz 1982). This is approximately main valley (Fig. 5b). The sequence consistsof a lower seriesof consistentwith the estimated magnitude of the earthquake lithifiedconglomerates, sands, clays, marly horizons and given by Ambraseys & Finkel (1987) but inconsistent with a minor lignites, unconformably overlain by alluvial fans near fault break 70 km long as suggested by Allen (1975). A fault the faults and Recent flood plain deposits along the centre of breakof 10-20kmalong the Buyiik Menderes,where the the basin. The Bozdogan and Karacasu bothhave faulted con- lengthof segments is observed to be less than 10 km,also tacts between alluvial deposits and basement on the west side suggests that more than one fault segment must have broken. of the grabens but generally have erosional contact with base- As in theGediz graben, there are few faultplanes pre- ment on the east side of the valley. servedas the footwall lithologies aredominantly Menderes Massif metamorphics or Neogenesediments. However, two faultsurfaces are observednear the village of Ortaklar Sediment dips (Fig. 5a) about 20 km west of Aydin on the north side of the valley (Fig.5a). At Omerbeyli, the fault plane exposure is Along the north side of the graben sediment dips in the Neo- about 12m2 and has an average dip of 44" and strike of 092". gene sequence are quite consistent (Fig. 5b) and in general are The surface is too badlyweathered to observeslickenlines. about 15-20' north. This is the sense of dip expected for rota- The exposure at Bozkoy (Fig. 5a) is only about 5 m' and has tion in the footwall of a south dipping normal fault. In places an average dip of 47" south and strikeof 087". Slickenlines are the observed dips are greater than 20" and more variable but observed onthis fault surface and show the motion to be this is due to the close proximity of either a major fault or a almost precisely pure dip slip. more minor intra-basinal fault. Thedips offaults in the Biiyiik Menderes fromearth- The Neogenesediments in theBozdogan andKaracasu quakesand fault exposures arecomparable, and approxi- grabendip generally west or southwest(Fig. 5b) atabout mately the same as estimates made in the Gediz graben. The 10-20". The observed dips are those expectedfor rotationin the average slip vector in the Biiyiik Menderes is approximately hanging wall of east dipping normal faults. The sediment dips north and the average dip on the faults is c. 45". in the 'cross-graben' are thus controlled mainly by faulting in

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 1040 S. PATON

Distance in kilometres NE SW Transect modelled in Fig. 6 NE SW (4 10 20 30 l I ~~~~ ~ ~ 'O r oi l 1 -1

-40 -50 l -40 L Distance in kilometres 10 20 30 40 50

Fig. 6. Bouguer gravity data from Geosystems (1990) report on Salihli area. The line of the transect (I) is shown in Fig. 2. Observed gravity (solid line) and calculated gravity (dotted line) Fig. 7. Bouguer gravity data from MTA (1979) contour map. The are shown in (a). The model used is shown in (b). The hatched area line of the transect (2) is shown in Fig. 2. Observed gravity (solid has a density contrast of -0.65 Mg m-3 with the surrounding rock. line) and calculated gravity (dotted line) are shown in (a). The The maximum depth to basement is c. 1.3 km. model used is shown in (b). The hatched area has a density contrast of -0.65 Mg m-3 with the surrounding rock. The maximum depth to basement is c. 1.4 km.

these graben and not by faulting in the major east-west-trending graben to the north. uplifted Neogene basin. To the northeast, there is an area with positive gravity anomaly which can be modelled as a layer c. Geophysics 300m thick with a density of 3.0 Mg m-3. Thegravity anomaly Detailed Bouguer gravity and magnetotelluric data are avail- coincides with theKula area where there are young basaltflows able for an areaof the Gediz Graben near Salihli (Geosystems and cones (Ercan 1982) and which may be expected to have an 1990; Fig. 2) and regional Bouguer gravity data (MTA 1979) associated gravity anomaly. coversthe whole area.Data from the smallscale regional Gravity modelling was also carried out in the Biiyiik Men- gravity map was modelled using a 2-D modellingprogram and deres graben (Fig.5a) which has a maximumdepth to basement compared with the detailed study of the Salihli area. The lines of c. 1.5 f 0.1 km (Fig. 9). The model shows possible faulting of the transects are shown on Fig. 2. A density contrast of in the northwith the deepestpari of the basin about 5 km to the 0.65 Mgm-3, between the basement (Menderes Massif meta- south of the main active fault. morphia) and sediments, was used in each case, because the In general, the models show a maximum depth to basement Geosystems (1990) report assumed an average density for the of 1.3-1.5 km in each graben, in agreement with AkCig (1988) basement of 2.8Mgrn-? and 2.15Mgm-3 for the sediments. who modelled unpublished gravity data, but there are distinct Figures 6 and 7 show the modelling from the detailed study lateral variations in this depth.Geosystems (1990) show a base- and regional data respectively and show reasonable agreement ment high tothe west of Salihli,with only a few hundred with a depth to basement of c. 1.3 f 0.1 km. The accuracy has metres of sediments, controlled by a N-S-trending structure. been estimated by testing different models and determining the The lateral variations are probably to some extent also con- best fit by eye. For these models no noticeable difference in fit trolled by segmentation onthe faults in a similar way to can be seen with depth to basement varying from 1.2 to 1.4 km. bathymetry being controlled by faulting at Evvia in central Both models also show a negative Bouguer gravityanomaly to Greece (Roberts & Jackson 1991). There is, however, no con- thesouth-west which correlates with the uplifted Neogene clusive evidence of significantly deeper basinsat the west end of basin described above. Since there is agreement between the the Gediz graben compared with the east end, as would be modelling of the two data sets, the regional map was used to expected if the extension increased to the west, although the model other areas. valley does become wider to the west. Thetransect to thenortheast of Salihli(Fig. 7) shows a A depth to basement of about 2 km, footwall uplift relative negative Bouguer gravityanomaly continuing to the northeast. to thevalley floor of about 2 km and afault dip of 35" givesthe The gravity anomaly correlates with the cross-graben structure horizontal extension across both grabensof about 6 km. Thisis which runs northeast from Adala (Fig. 3a) and has a modelled a minimum estimate as it assumes that deposition began as soon depth of c. 0.3 f 0.1 km. as faulting started which for a continental area may be un- A transect across the graben nearAlaSehir (Fig. 2) was also reasonable. It also assumes no erosion of the footwall: also modelled (Fig. 8) and has a maximum depth tobasement of c. unreasonable as erosion has obviously taken place. It does, 1.5 + 0.15 km. To the southwest of the deepest part of the however, compare reasonably well withthe estimates from basin, a shallower basin is present which correlates with the sediment dips (see below).

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 T ECT ON ICS AND SEDIMENTATION,TECTONICS AND SW TURKEY 1041

-50-40 t Distance in kilometres Distance in kilometres 10 20 30 40 50 10 40 fb) 20 30 50 60 70 I. 0

0.5 Iu 5 1.0 -E P 1.5

Fig. 8. Bouguer gravity data from MTA (1979) contour map. The Fig. 9. Bouguer gravity data from MTA (1979) contour map. The line of the transect (3) is shown in Fig. 2. Observed gravity (solid line of the transect is shown in Fig. 5, line X-Y. Observed gravity line) and calculated gravity (dotted 1ine)are shown in (a). The (solid line) and calculated gravity (dotted line) are shown in (a). model used is shown in (b). The hatched area has a density contrast The model used is shown in (b). The hatched area has a density of -0.65 Mg m-3 with the surrounding rock and maximum depth contrast of -0.65 Mg m-3 with the surrounding rock and to basement is c. 1.3 km. The dotted area has a density contrast of maximum depth to basement is c. 1.5 km. +0.2 Mg m-' and a maximum thickness of 0.5 km.

Faulting on the north side of the Gulf of Kerme Gulf (a distance of about 50 km). Instead there are breaks which occur at about10 km intervals (Fig. 10a): a similar situ- The north side of the Gulf of Kerme is marked by a distinct ation to that observed in the Gediz graben. The segments here E-W-trending scarp which, in places, rises from sea-level to are generally longer, however, suggesting that footwall litho- 1000 m (Fig.10a). The scarpis clearest from the east endof the logy is a major.factor. Thereis no evidence of a single distinct Gulf to just westof Oren. To the west of Oren the scarp fault linking the individual segments, becomes less distinct and the coastlineis less steep. Further to A major break in the scarp occurs at&en where a large fan the west, at Bodrum (Fig. l), there is no distinct scarp at all. has extended into the Gulf. This stepin the faultis also marked However, thereis a distinct scarp on the southside of the island by a NW-trending Neogene basin to the north. The NW-tren- of Kos with a bathymetric escarpment offshore which couldbe ding basin maybe analagous to the structures observedin both the continuation westwards (Koqyigit 1984; Westaway 1990). the Gediz and Biiyiik Menderes graben which are at a high In contrast, the south side of the gulf has subdued topo- angle to the main graben. graphy,the coastline having many bays, inlets and small islands just offshore. The difference suggests that the north side is being uplifted while the south side is subsiding due to the Basin tilting presence of a large normal fault. There are records of earth- Three basins with Neogene (probably Miocene to Pliocene) quakesin the area in 1933 (Ambraseys 1988; Jackson & sediments are situated in the footwall of the fault bounding the McKenzie 1988), in 1959 and in 1968 (McKenzie 1972, 1978). north sideof the Gulf (Fig. lob). The locationof the basins are The faultplane solutions for the 1959 (M, = 6.1) and 1969 probably not directly related to the position of the present (m,, = 5.5) events are both normal faults with a small, c. loo, active fault andso observed sediment dips are due to rotation in right-lateralcomponent. Unfortunately the earthquakes are thefootwall of the major E-W-trending fault. The west- very poorly located. Assuming, from the onshore exposure of ernmost basin has a small active fault on its west side but the the fault, that the south dipping plane from the fault plane throw on this fault is much less than the throw on the major solution is the fault plane, the1959 event has a dipof 76" and a fault, so it is the major fault that will dominate sediment dips strike of 065", both of which are poorly constrained, and the in the basin. 1968 event has a dip of 46" and a strike of 057" (McKenzie, The sediments within the basins range from limestones to 1972). These are approximately consistent with the features conglomerates with poorly developed coals exposed in some observed onshore. places. The finer grained limestones and marls are likely to The faultcomes onshorenear Oren where a degraded have been deposited close to the horizontal but now generally polishedfault surface with cemented limestone breccia is dip atangles of about5-10" northwards. In places greater dips present. This is a surface of about 1000m2 and has a dip of are recorded, but these are dueto the proximity of small faults about 55" south. As with the Gediz graben, the dipof the fault in a varietyof orientations: away from these areas theof dips the plane varies along strike. At various places along the coast the beds are fairly consistent. A major south-dipping normal fault Mesozoiclimestone, which is thedominant footwall litho- to the southof the basins would produce such a rotation about logy, is brecciated in a zone 1-5m wide. a horizontal axis. However, rotations of less than 10" suggest The scarp is not continuous along the whole length of the that little extension has taken place across the graben.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 1042 S. PATON

N S"-,, 4 Gulf of Kerme i t .- l --: I 25km l 25krn

Quaternary Neogene Fans/Fluvial 3 Pre-Neogene

Fig. 10. (a) Map showing faulting (thick lines) along the Gulf of Kerme. Ticks mark downthrown side. The arrow shows direction and dip of measured slickensides. The coastline is shown and land over 500m is stippled. (b) Geology of area shown on (a). Arrows give dip and dip direction of Neogene sediments.

Drainage patterns cpo, where (po and 'p, are the initial and final dips of the faults and J3 is the crustal extension). The calculated value is, within The drainage patternis strongly controlled by the positions of error,comparable withextension estimated fromboth the the active faults along the north side of the gulf. The faulting change in crustal thickness and the observed syn- and post- also controls the deposition of sediments. riftingsubsidence. Roberts & Jackson (1991)estimated the Many streamsflow southwards off the frontof the scarp but extension in central Greece using this method and a similar these are minor, have small drainage basins, and contribute approach will be used here. little sediment. Towards the west, where the scarp becomesless The seismogenic faults observed in western Turkey dip at marked, larger rivers with N-S drainage basins are developed between 35" and 55" and the associated tilting of sediments (Fig. 10a). These rivers can cut down into the footwall faster along the Gediz graben and Biiyiik Menderes graben is about thanit is beinguplifted, and so canerode backthe scarp 10-15" suggesting that the initial fault dips were greater than because, as the fault is now further to the south offshore, the 50". These observations give a value of1.2-1.3 for p. The exten- uplift along this section of coast is less than it is further east. sion across the Gulf of Kerme must be somewhat less as the The River Koca (Fig. 10a) rises about 50 km to the east of fault dips at about 55" and the sediments in the footwall dip at where it reaches the seaat &en. For much of its courseit flows less than loo, giving a value for J3 of only about 1.1. The Gediz parallel to the fault and between 10 and 20 km north of it. In graben, the Biiyiik Menderes and the Gulf of Kerme are the many places it forms avery distinct and narrowgorge. The size major E-W-trending active graben in southwestern Turkey and of the drainagebasin is about 1250 km2 andso it delivers much the calculations give an extensionacross the area from the sediment, as seen by the large fan where it reaches the sea. south side of theGulf of Kerme to northof the Gediz graben of Many tributaries flow northwards down the dip slope of the about 20 to 30 km. The horizontal extension across the Gediz uplifted fault block. The river can only cross the fault where and Biiyiik Menderes grabens was estimated, from the geo- the downcutting rate keeps up with the rate of footwall uplift. physical data, to be about 6 km in each case: a similar throw The River Koca only heads southwards to the sea at Ore, across the Gulf of Kerme gives atotal extension of about where the fault steps. Otherexamples of this geometry are seen 18 km, in reasonable agreement with the estimates from sedi- in central Greece (Roberts & Jackson 1991). ment dips. This small amount of extension fits in with a regional picture of extension increasing westwards, from zero on Discussion the Anatolian plateau to a maximumj3 value of about 2 in the central Aegean (Makris & Stobbe 1984). The observations described above can be used to addressvari- The three faultsystems studiedin this paper arehalf-graben, ous aspects of the extension in western Turkey. First, an esti- about 150 km long, with the major fault always on one sideof mate can be made for the amount of extension across the area the graben i.e. there is no change of polarity along strike. The studied, and secondly general points can be made about the systems are therefore similar to the Gulf of Corinth, central relationship between faulting, drainage, and sedimentation. Greece, but different from theGulf of Evvia, where the polarity Studies in the North Sea (White 1990) and South ChinaSea of the half-graben changes along strike (Roberts & Jackson (Su et al. 1990) have found that the initial and final dips of 1991). faults which bound tilted blocks can be used to estimate the Normalfaulting dominates the morphology of western extension using the simple domino model (i.e. p = sin cpdsin Turkey and thus has a majorinfluence on drainage anddeposi-

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 T E C TO N IC S AND SEDIMENTATION,TECTONICS AND SW TURKEY 1043

tional patterns. One of the most important features of this is Biiyiik Menderes. I thank D. McKenzie, D. Latin and J. Jackson for fault segmentation which controls where the major rivers will reading the manuscript and for useful discussion. Financial support is cut through the line of the fault. Theserivers carry the largest provided by a Shell Studentship for which I am very grateful. This sediment loads and so dominate deposition in the area. The paper is Earth Sciences contribution no. 2298. largest fans with the coarsest sediments developat the ends of fault segments. In areas like western Turkey with high runoff and erosion, the main axial drainage along the length of the References graben may be pushed to the opposite side of the valley from AKCIG,Z. 1988. BatiAnadolu’nun yapisal sorunlarinin gravite verileri ile ir- the main bounding fault by these fans. delenmesi (in Turkish with English abstract). Geological BuNetin of Turkey, Footwalllithology also plays animportant role in con- 31, 63-70. trolling drainage patterns. Where the lithology is resistant to ALLEN,C. R. 1975. Geologicalcriteria for evaluating seismicity. Geological Society of America Bulletin, 86, 1041-1057. erosion (as in the limestone on the north side of the Gulf of AMBRASEYS,N. N. 1971. Value of historical records of earthquakes. Nature, 232, Kerme) the major drainage in the footwall is parallel to the 375-379. fault, only cutting through to the seawhere the fault scarp dies -1988. Engineering seismology.Earthquake Engineering and Structural Dyna- out at a segment boundary. In the Gediz graben, where the mics, 17, 1-105. -& FINKEL,C. F. 1987. The seismicity of the N. E. Mediterranean region dominant footwall lithology is friable Neogene sediments, the during the early twentieth century. Annales Geophysicae, 56, 229-252.

rivers are generally perpendicular to the length of the graben ~ & TCHALENKO,J. S. 1972. Seismotectonic aspects of the Gediz, Turkey, and cut deeply into the footwall. In this situation, thereis also earthquake of March 1970. Geophysical Journal of the Royal Astronomical more chance of antecedent drainage being able to keep pace Society, 30, 229-252. ARMIJO,R., TAPFONIER, P., MERCIER,J. L. & TONG-LIN,H. 1986. Quaternary with uplift in the footwall block. extension in south Tibet: field observations and tectonic implications.Jour- Footwalllithology also seems to beimportant in nal of Geophysical Research, 91, 803-872. determining the length scale of the segmentationof the faults. ARPAT,E. & BINGOL,E. 1969. The rift system of the western Turkey; thoughts on In limestone the faultsare more continuous along strike (about its development. Bulletin of the Turkey Mineral Exploration Institute, 78, 33-39. 15 km) whereas in more friable sediments the segments are BECKER-PLATEN,J. D. 1970.Lithostratigraphische Untersuchungen im- somewhat shorter. However, the maximum segment length is kanozoikum Sudwest Anatoliens (Turkei). Beihefte Geologischen Jahrbuch, of a similar length to the thickness of the seismogenic layer 97, 244. (15-20 km). Earthquakes seem to be able to rupture more than BENDA, L., MEULENKAMP,J. E. & WEERD,A. 1977. Biostratigraphic correlations in theeastern Mediterranean Neogene. Newsletter of Stratigraphy, 6, one fault segment, as inferred for the 1899 event near Aydin, 117-130. and seen in the 1971 Gediz earthquake, alsoin western Turkey DE POLO,C. M,,CLARK, D. G.,SLEMMONS, D. B. & RAMELLI,A. R. 1991. His- (Ambraseys & Tchalenko 1972). torical surface faulting in the Basin and Range province, western North America: implications for fault segmentation.Journal of Structural Geology, Conclusions 13, 123-136. ERCAN, T.1982. Kula yoresinin jeolojisi ve volkanitlerinin petrolojisi. Istanbul The area of western Turkey discussed in this paper is in many Yerbilmleri, 3, 77-124. ways comparable to the area of Central Greecestudied by EYIDOEAN,H. & JACKSON, J.A. 1985. A seismological study of normal faulting in the Demirci, Alasehirand Gediz earthquakes of 1969-1970 in W. Turkey: Roberts & Jackson (1991). Both areas are in the actively de- implications for the nature and geometry of deformation in the continental forming regionof the Aegean and consist ofa number of fault crust. Geophysical Journal of the Royal Astronomical Society, 81, 569-607. boundedgraben. In western Turkey the graben are clearly GARFUNKEL,2. & BARTOV,Y. 1977. The tecronics ofthe Sue: Rift. Bulletin of the asymmetricwith small antitheticfaults on one side ofthe Geological Survey of Israel, 71. GEOSYSTEMS1990. Gediz Graben: Final Report on the interpretation of gravity, graben and are about10-20 km wide; the major faultis always magnetic, electromagnetic and magneto-telluric surveys. Milan, Italy. restricted to one side of the graben and does not change pol- GILBERT,G. K. 1928. Studies qfBasin and Range Structure. United States Geo- arity. The extension across the graben is only about 6-10 km, logical Survey Professional Paper, 153. suggesting that the wholeregion has undergone only small HANCOCK,P. L. & BARKA.A. A. 1987. Kinematic indicators on active normal faults in western Turkey. Journal of Structural Geology, 9, 573-584. degrees of extension. HATZFELD, D.,CHRISTOWULOU, A., SCORDILIS, E., PANAGIOTOFOULOS,D. & Fault segmentation is observed in all the major grabens. HATZIDMITRIOU,P. 1987. A microearthquakestudy oftheMygdonian graben These segments are not linkedby single ‘transfer’ faults butdo (N. Greece). Earth and Planetary Science Letters, 81, 379-396. provide places where rivers can cut through the line of the JACKSON,J. A. & MCKENZIE, D. P. 1988. Rates ofactive deformation in the fault. Tranverse structures at a high angle to the main graben Aegean Sea and surrounding regions. Basin Research, 1, 121-128. - & WHITE,N. J.1989. Normal faulting in theupper continental crust: are also present. Both of these features are important in con- observations from regions ofactiveextension.Journa~ofSrrucruralGeology, trolling sediment deposition. If the footwall lithology is fri- 11, 15-36. able, poorly consolidated sediments the drainage is generally -, GAGNEPAIN,J., HOUSEMAN,G., KING, G. C.P,, PAPADIMITRIOU,P,, in linear valleys, whereas in resistant lithologies axial drain- SOUFLERIS,C. & VIRIEUX,J. 1982. Seismicity, normal faulting, andthe geomorphologicaldevelopment of theGulf of Corinth (Greece):the age in the footwall is more important. Rivers that have axial Corinth earthquakes of February and March 1981. Earth and Planetary drainage in the footwall and cut through the faultat the endof Science Letters, 57, 377-397. a segment have the largest drainage basins, and will therefore KING,G. C. P,, OUYANG,Z. X., PAPADIMITRIOU,P,, DESCHAMPS, A., GAGNEPAIN, supply the greatest sediment load to the graben floor. S., HOUSEMAN,G., JACKSON,J. A., SOUFLERIS, C.& VIRIEUX,J. 1985. The evolution of the Gulf of Corinth (Greece): an aftershock study of the 1981 The Gediz graben has at least two phases of faulting, with earthquakes. Geophysical Journal of the Royal Astronomical Society, 80, successive periods involving the main graben bounding fault 677493. stepping into the hanging wall. The new fault then uplifts the KISSEL,C. & LAJ,C. 1988. The Tertiary geodynamical evolution of the Aegean basin fill from the older fault. Such stepping has been predic- arc: a paleomagnetic reconstruction. Tectonophysics, 146, 183-201. KOCYIGIT,A. 1984. Guneybati Tiirkiye ve yakm doldyindi levha ici yeni tektonik ted from sand-box models. gelisim (in Turkish withEnglish abstract). Geological Society of’ Turkey Bulletin. 27, 1-16. LEEDER, M.R. & ALEXANDER,I. 1987. The origin and tectonic significance of I am grateful to Y. Yilmaz and C. Sengor for help and support in asymetrical meander belts. Sedimentulugy, 34, 217-226. Turkey, and S. Roberts forallowing me to use his thesis work from the LE PICHON,X. & ANGELIER,I. 1979. The Hellenic arc and trench system:a key to

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021 1044 S. PATON

the neotectonic evolution of the eastern Mediterranean area.Tectonophysics, ZOLLWEG,I. E. &KING,J. J. 1987. The Borah Peak, Idaho earthquake and 60, 142. its aftershocks. Geological Society ofAmerica Bulletin, 77, 694. LDTTIG, G.& STEFFENS,P. 1976. Explanatory notes for the paleographic atlas of ROBERTS,S. & JACKSON,J. 1991. Active normal faulting in central Greece: an Turkey from theOligocene to the Pleistocene. Bundesanstalt fur Geowis- overview. In: ROBERTS, A.M,, YIELDING,G. & FREEMAN,B. (eds) The Geo- senschaften und Rohstoffer, Hannover. metry of Normal Faults. Geological Society, London, Special Publication, LYON-CAEN, M.,ARMIJO, R.,DRAKOPOULOS, J., BASKOUTAS, J., DELIBASSIS, N., 56, 125-142. GAULON,R., KOUSKOUNA, V., LATOUSSAKIS,J., MAKROPOULOS, PAPK., ROBERTS,S. C. 1988. Active normal faulting in central Greece and western Turkey. ADIMITRIOU, P,, PAPANASTASSIOU,D. & PEPEWTTI, G. 1988. The 1986 Kal- PhD Thesis, University of Cambridge. amata (S. Peloponessos) earthquake: detailed study of a normal fault and RUSSEL,1. C. 1895. Lakes of North America: a reading lesson for students of tectonic implications. Journal of Geophysical Research, 93, 14967-15000. geography and geology. Ginn, Boston & LONDON. MCCLAY,K. R. & ELLIS,P. G. 1987. Analogue models of extensionalfault SAROGLU,F., EMRE,b. & BORAY,A. 1987. Turkiye Diri Fay Haritasi (Map of geometries. In: COWARD, M. P,, DEWEY,J. F. & HANCOCK,P. L. (eds) Con- active Turkish faults). Unpublished. tinental Extensional Tectonics. Geological Society, London, Special Publi- SCHAFFER,F. 1900. Das Meanderthallenvorn 20 September1899. Mitlewist Klass cation, 28, 109-125. Geographische Gestalt (Vienna), 43, 221-23 I. MCKENZIE, D. P. 1972. Active tectonics of theMediterranean region.Geophysical SCHOLZ,C. H. 1982. Scaling laws for large earthquakes: consequences for physi- Journal ofthe Royal Astronomical Society, 30, 109-185. cal models. Bulletin of the Seismological Society of America, 12, 1-14. - 1978. Active tectonics of the Alpine-Himalayan belt: the Aegean Sea and $ENCOR, C.M. 1987. Cross faults and differential stretching of hanging walls in surrounding regions. Geophysical Journalofthe Royal Astronomical Society, regions of low-angle normal faulting: examples from western Turkey. In: 55, 21 7-254. COWARD, H. P,, DEWEY,J. F. & HANCOCK,P. L. (eds) Continental Exten- MADEN TEKTIKVE ARAMA (MTA) (Directorate of Mineral Research and Explor- sionalTectonics. GeologicalSociety, London, SpecialPublication, 28, ation, Turkey) 1979. Bouguer gravity map of western Turkey. Unpublished. 575-589. MAKRIS,J. & STOBBE,C. 1984. Physical properties and state of the crust and SOUFLERIS,C., JACKSON,J. A., KING, G., SPENCER, C.& SCHOLZ,C. 1982. The upper mantle of the eastern Mediterranean area. Tectonphysics, 60, 142. 1978 earthquake sequence near Thesaloniki (N. Greece). Geophysical Jour- MERCIER, J. L., DELIBASSIS, N.,GAUTIER, A., JARRIGE,J. J., LEMILLE,F., PHIL- nal of the Royal Astronomical Society, 68, 429458. LIP, L., SEBRIER,M. & SOREL,D. 1979. La neotectonique de I’Arc Egeen. STEININGER,F. F., Rffi~,F. & NEVESSKAJA,L. A. 1985. Neogene ofthe Mediter- Revue de Geologie Dynamique et de Geographie Physique, 21, 67-92. ranean Tethys and Paratethys. Vienna. -, SOREL,D. & SIMEAKIS,K. 1987. Changes of the state of stress in the over- Su DAQUAN, WHITE,N. & MCKENZIE,D. 1990. Extension and subsidence of the iding plate of a subduction zone: the Aegean Arc from the Pliocene to the Pearl River Mouth basin, northern South China Sea. BasinResearch, 2, present. Annales Tectonicae, 1, 20-39. 205-222. --, , VERGELY,P. & SIMEAKIS,K. 1389. Extensional tectonic regimesin the STEWART,I. S. & HANCOCK,P. L. 1991. Scales of structural heterogeneity within Aegean basins during the Cenozoic. Basin Research, 2, 49-71. neotectonic normal fault zones in the Aegean region. Journal of Structural METEOROLOGICALOFTICE 1958. Tables oftemperature, relative humidity and pre- Geology, 13, 191-204. cipitation for the world. HMSO, London. WESTAWAY,R. 1990. Block rotation in western Turkey I. Observational evidence. PROFFET,J. M. 1977. Cenozoic geology of the Yerrington district, Nevada, and Journal of Geophysical Research, 95, 19857-19884. implications for the nature and origin of Basin and Range faulting. Geo- WHITE,N. 1990.Resolving the extension discrepancy in theNorth Sea. In: logical Society of America Bulletin, 88, 247-266. BLUNDELL, J.D. & GIBBS,A. (eds) Tectonic evolution of the North Sea Rifts. RICHING,W. D., PECHMANN,J. C., SMITH,R. B., LANCER, C.J., GOTER,S. K., Oxford University Press, 217-239.

Received 29 July 1991; revised typescript accepted 18 May 1992.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/149/6/1031/4892144/gsjgs.149.6.1031.pdf by guest on 01 October 2021