Geological and palaeoseismological evidence for late Pleistocene−Holocene activity on the Manisa fault zone, Western Anatolia

In West Anatolia near the cities of İzmir and Manisa, the historical occurrence of large earthquakes suggests the presence of important seismogenic faults. However, these faults have yet to be investigated in detail. The Manisa Fault Zone (MFZ) is an active large-scale normal fault system in this area, and thus field observations and palaeoseismological studies of this zone are important for predicting future earthquakes.

Geological and Palaeoseismological Evidence for Late Pleistocene−Holocene Activity on the Manisa Fault Zone,

Western Anatolia

ÇAĞLAR ÖZKAYMAK1, HASAN SÖZBİLİR1, BORA UZEL1 & H SERDAR AKYÜZ2

1

Dokuz Eylül University, Engineering Faculty, Department of Geological Engineering, Tınaztepe Campus,

Buca, TR−35160 İzmir, Turkey (E-mail: caglar.ozkaymak@deu.edu.tr)

2

İstanbul Technical University, Faculty of Mines, Department of Geological Engineering,

Maslak, TR−34469 İstanbul, Turkey

Received 23 July 2009; revised typescripts receipt 15 March 2010, 24 August 2010 & 22 October 2010;

accepted 08 November 2010

Abstract: In West Anatolia near the cities of İzmir and Manisa, the historical occurrence of large earthquakes suggests

the presence of important seismogenic faults However, these faults have yet to be investigated in detail Th e Manisa Fault Zone (MFZ) is an active large-scale normal fault system in this area, and thus fi eld observations and palaeoseismological studies of this zone are important for predicting future earthquakes Hence we sought to document geological and palaeoseismological evidence for Holocene activity on the MFZ We performed trenching to determine the magnitude and timing of past surface-faulting events using detailed fault-trace mapping, measurements of Upper Pleistocene− Lower Holocene sediments, and radiocarbon dating By comparing the trench data with palaeoearthquake records, we

fi nd evidence for three palaeoearthquakes which correspond to 926 AD, 1595 or 1664 AD, with the most recent event

in 1845 AD We also fi nd this in the central and western sectors of the MFZ, which together with the eastern sector comprise the three major seismogenic zones Th e Pliocene−Quaternary vertical off set at fault scarps is far less than that

in the western sector, suggesting that activities of these sectors are highly independent Evaluation of fi eld observations suggests that the MFZ has been the source of multiple Late Pleistocene and Holocene surface-rupturing earthquakes Our results constitute the fi rst palaeoseismic evidence on the causative faults of historical earthquakes that aff ected Manisa, and point to their underlying tectonic mechanisms.

Key Words: Manisa Fault Zone, palaeoseismology, late Pleistocene, Holocene, Gediz Graben, Western Anatolia

Manisa Fay Zonu’nun Geç Pleyistosen−Holosen Aktivitesine Ait Jeolojik ve

Paleosismolojik Veriler, Batı Anadolu

Özet: Batı Anadolu’da İzmir ve Manisa şehri yakınlarında tarihsel dönemlerde büyük depremlerin meydana gelmiş

olması, bu bölgede önemli sismojenik fayların varlığına işaret etmektedir Ancak, bu faylar şimdiye kadar ayrıntılı bir şekilde araştırılmamışlardır Bu bölgede bulunan Manisa Fay Zonu (MFZ) büyük ölçekli aktif normal fay sistemidir

ve bu zon üzerinde gerçekleştirilen arazi gözlemleri ile paleosismolojik çalışmalar, gelecekteki depremlerin tahmin edilebilmesi açısından önemlidir Bu çalışmada, MFZ’nun Holosen aktivitesine ait jeolojik ve paleosismolojik veriler sunulmuştur Tarihsel dönem yüzey faylanmalarının zamanını ve büyüklüklerini ortaya çıkarmak amacıyla, ayrıntılı fay izi haritalaması, geç Pleyistosen−erken Holosen yaşlı sedimanların incelenmesi, radyokarbon yaşlandırma yöntemleri kullanılarak hendek çalışmaları gerçekleştirilmiştir Hendek verileriyle eski deprem kataloğu bilgileri karşılaştırıldığında üç depreme ait izler saptanmıştır; bunlar sırasıyla, 926, 1595 veya 1664 ve 1845 depremlerine karşılık gelmektedir Ayrıca, batı, orta ve doğu bölgelerden oluşan üç ana sismojenik zon tanımlanmıştır Fay sarplığının Pliyosen−Kuvaterner zamanındaki düşey atım miktarının batı bölümde daha az olması bu bölümlerin bağımsız olarak hareket ettiklerini göstermektedir Arazi çalışmaları, MFZ’nun geç Pleyistosen ve Holosen’de bölgede meydana gelen ve yüzey kırığı oluşturan depremlerin kaynağı olduğunu göstermektedir Elde edilen sonuçlar, Manisa şehrini etkileyen tarihsel depremlere neden olan faylar ve bu fayların tektonik mekanizmaları üzerine elde edilen ilk paleosismolojik verileri oluşturmaktadır.

Anahtar Sözcükler: Manisa Fay Zonu, Paleosismoloji, Geç Pleyistosen, Holosen, Gediz Grabeni, Batı Anadolu

Western Anatolia represents a good example of

post-collisional extensional tectonics dominated by

approximately E–W-trending active normal faults

(with maximum lengths typically in the range of

15–25 km), as well as NE–SW- and NW–SE-trending

active strike-slip faults (Figure 1a; Dewey & Şengör

1979; Şengör & Yılmaz 1981; Jackson & McKenzie

1988; Eyidoğan & Jackson 1985; Şengör et al 1985;

Şengör 1987; Seyitoğlu & Scott 1991; Sözbilir 2000,

2005; Bozkurt 2001; England 2003; Koçyiğit & Özacar

2003; Lenk et al 2003; Kaymakçı 2006; Sözbilir et al

2006, 2007, 2008, 2009; Özkaymak & Sözbilir 2008;

Uzel & Sözbilir 2008)

In the western part of West Anatolia, near the cities

of İzmir and Manisa, the historical occurrence of

large earthquakes suggests the presence of important

seismogenic faults, although none have yet been

investigated in detail One such active large-scale

normal fault system is the Manisa Fault Zone (MFZ),

which exhibits prominent Quaternary fault scarps

and signifi cant morphologic variations (Figure 1b;

Bozkurt & Sözbilir 2006; Özkaymak & Sözbilir 2008)

Th erefore, the MFZ itself is a likely source of future

earthquakes in the region, and thus fi eld observations

of Holocene activity and palaeoseismological studies

of this fault zone are important for predicting future

earthquakes (Hakyemez et al 1999; Emre et al 2005;

Bozkurt & Sözbilir 2006; Çift çi & Bozkurt 2007, 2008,

2009; Özkaymak & Sözbilir 2008)

palaeoseismological data for the MFZ, aims

for the fi rst time to document geological and

palaeoseismological evidence for Holocene activity

Trenching was carried out across the westernmost

segments to determine the magnitude and timing of

past surface-faulting Th e report includes a detailed

map of the studied area at a scale of 1/5000, the

logging of two trench walls across the Paşadeğirmeni

fault zone, measurements of a stratigraphic section

of the upper Pleistocene–lower Holocene sediments,

and radiocarbon dating

Seismotectonic Setting

Th e Aegean and surrounding area is considered to be

one of the most seismically active regions of the world

where N–S-trending contraction is overprinted by N–S-trending extension from at least Pliocene times

(Şengör et al 1985; Seyitoğlu & Scott 1991; Taymaz

et al 1991; Pavlides 1996; Papazachos & Papazachou

1997; Altunel 1998, 1999; Koçyiğit et al 1999; Akyüz

& Altunel 2001; Bozkurt 2001; Caputo et al 2004;

Pavlides & Caputo 2004; Caputo & Helly 2005, 2008;

Akyol et al 2006; Özkaymak et al 2008, 2009) Th e studied area, between longitudes of approximately 27° to 28° and latitudes of approximately 38.3° to 38.7° north, is deformed by two active fault systems: strike-slip and dip-slip faults (Figures 1a & 2) Th e former are characteristically NE–SW-trending dextral and NW–SE-trending sinistral strike-slip faults, while the latter dip-slip normal faults are mainly E–W oriented (Figure 2a) Th ese active tectonic structures work together and are responsible for most of the earthquakes that occurred in both historical and

instrumental periods in the region (Taymaz et al 1991; Emre et al 2005; Akyol et al 2006; Zhu et al 2006; Aktar et al 2007; Sözbilir et al 2008, 2009; Tan

et al 2008; Uzel et al 2011).

Although the İzmir-Manisa region has not suff ered destructive earthquakes between 1902 and

2010, several publications containing information about large historical earthquakes that damaged cities

in the region (Ergin et al 1967; Soysal et al 1981; Ambraseys 1988; Guidoboni et al 1994; Ambraseys

& Finkel 1995; Papazachos & Papazachou 1997;

Ambraseys & Jackson 1998; Tan et al 2008) Table

1 summarizes the descriptions of large historical earthquakes that aff ected the region (Figure 2a) and specifi cally damaged the city of Manisa

One of the best-documented historical earthquakes in West Anatolia is the event in 17 AD According to Ambraseys (1988), 16 ancient cities, most of them located within the Manisa Basin, collapsed and were damaged by the event (Table

1) Soysal et al (1981) and Guidoboni et al (1994)

noted that 13 cities were completely demolished

by this event Some researchers affi rm that the 17

AD earthquake occurred along the Gediz Graben (Ambraseys & Jackson 1998), but other studies give the location as the Muradiye district (western part

of Manisa, Figure 2a) with an intensity of IX (Soysal

et al 1981; Guidoboni et al 1994; Tan et al 2008)

According to Guidoboni et al (1994), it was the

and slope deposits

detachment fault

and shear zone

detachment fault

and shear zone

major thrust and suture zones major thrust and suture zones

Karaburun Platform Sakarya Zone Menderes Massif

Ma

F

PAF

Ta F

asin

Demi

rci Basin

MFZ

Gör

des

Basin

Gördes

Basin

Büyük Menderses detachment fault Büyük Menderes detachment fault

Büyük Menderes Graben

İzmir Manisa

EF

Bakır

çay GrabenBakırça

y Graben

BasinBasin

Sele

ndiSelendi

OFZOFZ

Quaternary alluvial fan

normal and/or oblique fault

sinistral strike-slip faulting (earlier motion)

pre-Neogene basement rocks

detachment fault and shear zone

Karaburun Platform Sakarya Zone Menderes Massif

dextral strike-slip faulting (the latest motion)

a

Gediz Graben

Gedi

z Graben

Gediz detachment fault

Figure 1 (a) Outline geological map of western Turkey showing major tectonostratigraphic units and

location of the study area (compiled from Okay & Siyako 1993; Bozkurt & Park 1994; Bozkurt

2001, 2004; Sözbilir 2001, 2002, 2005; Collins & Robertson 2003; Özer & Sözbilir 2003; Bozkurt

& Sözbilir 2004; Işık et al 2004; Özkaymak & Sözbilir 2006, 2007, 2008) Abbreviations EF, İF,

MFZ, and OFZ, refer to the Efes Fault, İzmir Fault, Manisa Fault Zone, and Orhanlı Fault

Zone, respectively Inset shows the location of Figure 1 Bold dotted lines indicate the location

of the İzmir-Balıkesir Transfer Zone; white and black arrows show the reactivation of the

transfer zone as sinistral and dextral strike-slip faults, respectively (b) Simplifi ed geological

map showing the curvature of the Manisa Fault Zone (compiled from Bozkurt & Sözbilir 2006;

Özkaymak & Sözbilir 2008) See Figure 1a for location of the map Abbreviations PFZ, GFZ,

MaF, TaF, KeF, and MFZ, refer to the Paşadeğirmeni Fault Zone, Gürle Fault Zone, Manastır

Fault, Taşlıburun Fault, Keçiliköy Fault, and Manisa Fault Zone, respectively.

largest and most damaging earthquake ever known

in the Manisa Basin An intensity distribution map

of the 17 AD earthquake (Guidoboni et al 1994)

shows a relatively large amount of damage to 13

ancient cities; the authors mention that especially in

Magnesia (Manisa) and Sardeis (Sart), located almost

at the centre of the intensity map, there were wide and

deep surface ruptures Twenty-seven years aft er this

event, in 44 AD, the ancient cities of Magnesia and Ephesus (Efes) were shaken by an earthquake with

an intensity of VIII (Ergin et al 1967; Soysal et al

1981, Table 1) Ambraseys & Jackson (1998) refer to

an earthquake in Manisa in August of 926, although there is no detailed information about this event Ambraseys & Finkel (1995) and Ambraseys & Jackson (1998) reported an earthquake that caused

1595(6,8)

17(6)

17(2,3)

926(6,8) 44(2,8)

instrumental earthquakes (M: 5.4 - 2.6)

L1

L2

strike-slip faults normal faults

inferred faults

elevation (m)

KF İF

O FZ OFZ

0

b

Figure 2 (a) Seismotectonic map of the İzmir-Manisa region, showing the epicentres of both instrumental and historical earthquakes

Instrumental earthquakes exceeding M 5.4 are reported from 1902 to 2010 Magnitude is shown by the size of the red-fi lled circles Epicentres of historical earthquakes that aff ected the region and specifi cally damaged the city of Manisa are shown

by blue stars Dates and coordinate references (given in brackets) of the historical earthquakes are given above or to the right of the symbol (see Table 1, for details) Th e map also shows fault-plane solutions of two earthquakes (L1: 28.01.1994, Mb: 5.2 and L2: 16.12.1977, Mb: 5.3) Abbreviations MFZ, KaF, İF, KF, and OFZ, refer to the Manisa Fault Zone, Karaçay

Fault, İzmir Fault, Kemalpaşa Fault, and Orhanlı Fault Zone, respectively (b) A cross section across the Manisa Fault

Zone showing the hypocentre and epicentre of the Manisa earthquake on 28.01.1994 Th e location of focal depth and the

epicentre of the earthquake are taken from Taymaz et al (2004) and Tan et al (2008) Note that the dip of the surface-slip

vector (53°) was measured in the fi eld, while the dip of the fault at the hypocentre (43°) was obtained from the fault-plane solution Th e hypocentre of the earthquake is marked by a red-fi lled star

surface ruptures between the cities of Manisa and

Ahmetli on 22 September 1595 Another earthquake

in İzmir on 2 June 1664 with an intensity of VII has

been reported (Ergin et al 1967; Soysal et al 1981;

Ambraseys & Finkel 1995) According to Ambraseys

and Jackson (1998), this earthquake occurred near

İzmir, probably in Manisa Th e last historical and

destructive earthquake, which damaged the city of

Manisa, occurred on 23 June 1845 (Ergin et al 1967;

Soysal et al 1981) Th e location of this earthquake is

given as the city centre of Manisa, and its intensity was

VIII (Soysal et al 1981) According to Papazachos

& Papazachou (1997), the MFZ is thought to have

produced historically signifi cant earthquakes such as

the M= 6.7 event in 1845, and fault activity was also

manifest during an M= 5.2 earthquake in 1994

Th e instrumental earthquake data of Figure

2a, whose magnitudes range from 2.6–5.4 in the

rectangular area specifi ed by the coordinates, are

acquired from sources documented by Tan et al

(2008) and KOERI (2010) According to these reports,

the most recent earthquakes occurred on 28 January

1994 near Manisa with a magnitude of 5.2 at a depth

of 10 km (Figure 2b) and on 16 December 1977 near

İzmir with a magnitude of 5.3 at a depth of 24 km

(Tan et al 2008) Solutions of their focal mechanism

indicate the existence of normal faulting with a minor

right-lateral slip component (Figure 2a) Th e Manisa

earthquake triggered 13 aft ershocks within two

months aft er the main shock, all recorded by a local

seismic network (KOERI) Th e spatial distribution

of the main shock and aft ershocks with magnitudes between 3.5 and 4.0 shows that these shocks form

a cluster approximately 10 km away from the MFZ (Figure 2a) As Figure 2b shows, this event appears

to have a focal depth of up to 10 km which indicates that recent earthquakes in the Manisa Basin originate near the base of the brittle upper crust

Th e Manisa Fault Zone: Fault Geometry and Segment Characteristics

Th e fault zone, a 35-km-long northeastward arched active corrugated fault system with distinct along-strike bends, trends NW–SE for some distance in the southeast, then bends into an approximately E–W direction in the north (Figure 1b, Bozkurt & Sözbilir 2006) It cuts and displaces Miocene lacustrine carbonates in the footwall and Upper Pleistocene to Holocene deposits in the hanging wall Th e eastern sector of the well-defi ned fault trace has been mapped

in detail for more than 15 km (Bozkurt & Sözbilir 2006) and can be followed westwards up to a possible total length of about 35 km (Özkaymak & Sözbilir 2008) According to geological and geomorphological investigations, the MFZ has been geometrically and kinematically characterised as a typical Aegean-type active fault similar to the Tyrnavos Fault (Th essaly,

Central Greece) (Caputo et al 2004).

Th e MFZ was divided into separate segments arranged en échelon Individual array length varies from one to several kilometres During the early

Table 1 List of recorded historical earthquakes in the Manisa region References: (1) Ergin et al 1967; (2) Soysal et al 1981; (3)

Ambraseys 1988; (4) Guidoboni et al 1994; (5) Papazachos & Papazachou 1997; (6) Ambraseys & Jackson 1998; (7) Ambraseys

& Finkel 1995; (8) Tan et al 2008 I– intensity M– magnitude.

Manisa (Magnesia), Muradiye, Sart (Sardes) (2); Magnesia, Sardes, Temnos, Myrina, Ephesus, Appolonia, Hyrcanis,

VS Mostheni, Aegae, Hierocaesaria, Euthena, Ulloron, Philadelphia, Tmolus, Cyme, Th yatira (3); Gediz River (6)

IX (2) 7.4 (4, 8) 1, 2, 3, 4,

6, 8

4 September 22 1595 (6, 7) 38.50–27.90 (6) Manisa, Urganlı, Sart, Ahmetli, Gedik, Bostancı, Hamza

linkage stage, faults were not connected but remained

as isolated fault segments separated by a distorted

ramp (soft linkage) or transfer fault (Figure 3a) As

the faults grew, the fault segments became connected

along the strike to form a continuous zigzag-shaped

fault trace (hard linkage) Th us, kilometre-scale

segmentation occurs as the displacement changes

from one fault to another and is accommodated

either by a relay ramp or transfer fault (Figure 3b, c)

Similar segmentation has been described in Greece

(Roberts & Jackson 1991)

Our studies suggest that the courses of some northeast-fl owing rivers, which correspond to the NE–SW-striking faults, may mark segment terminations One of these is the Kırtık River, which enters the graben 1 km southeast of Manisa (Figure 3b) where the MFZ bends to align E–W To the west, the Karaçay River, 6 km west of Manisa, enters the graben where there is an off set in the fault of about 0.5 km Th e Gürleçayı River enters the graben at the end of the Manastır Fault (Figures 3 & 4) Th ese rivers carry the largest sediment loads and thereby

early fault geometries prior to linkage post-linkage geometry

KocR ER

sinistral strike-slip fault

normal fault dextral strike-slip fault

500 1000 1500

0 m altitude

alluvial fan

c

Figure 3 Fault geometry and segment characteristics of the Manisa Fault Zone (a) Early fault geometry prior to linkage, (b)

post-linkage geometry of the fault zone, (c) a 3D block diagram showing present-day confi guration of the study area

Note that the large alluvial fans frequently take advantage of transfer fault zones and areas between en échelon faults Note also that early fault segments are 5 km long on average prior to linkage; but aft er linkage and breaching of the fault segments, the fault zone resulted in three main segments of about 10 to 15 km long Abbreviations GuR, KaR, KoR, ÇaR, KıR, SıR, KocR and ER refer to the Gürleçayı River, Karaçay River, Kocadere River, Çaybaşı River, Kırtık River, Sırtlangöçü River, Kocakızıl River and Eşref River respectively

dominate lateral alluvial fan deposition in the area

Th us, the largest fans with the coarsest sediments

develop at the ends of fault segments Th ese NE–

SW-trending strike-slip faults (i.e the Gürle Fault

Zone (GFZ) and the Karaçay Fault (KaF)) are clearly

recognised by morphologically deep valleys in the

west and east of the study area (Figures 1b & 3)

Th e Karaçay Fault comprises several well-exposed

fault surfaces with a relief of 5 to 10 m and displays

well-preserved slickensides Structural observations

on these slickensides show that the Karaçay Fault

is a polyphase structure Evidence for reactivation

is similarly established on the slip surfaces of NW–

SE-striking normal faults (see Özkaymak & Sözbilir

2008 for a detailed description of NE–SW-trending

strike-slip faults) Th e GFZ is about 1.5 km wide,

and consists of parallel-subparallel bifurcated fault

segments which juxtapose Neogene volcanic rocks

and the Bornova Flysch Zone Th is fault is cut by the

NW–SE-striking Paşadeğirmeni Fault Zone (PFZ)

which can be traced northwest of Paşadeğirmeni

Hill as a single fault about 4 km long: to the SE it

consists of two fault branches about 3 km long In the

southeastern part of the PFZ, we mapped three en

échelon faults, one of which is the Manastır Fault Th is

fault, which is 4.5 km long, defi nes the southwestern

boundary of the Manisa Basin Its trace is marked by

large well-preserved scarps with maximum heights

of 140 m, a series of screes, landslides, and triangular

facets Along the range-front, the faceted spurs show

at least two generations of facets (Figure 3c) Th is

suggests that the front has experienced at least two

uplift periods separated by tectonic quiescence Th e

bottom of the front shows evidence of very recent

movement, such as a well-preserved and continuous

scarp Th e scarps have all the main characteristics

of the fault scarps described in diff erent erosion

models (e.g., Wallace 1977; Nash 1980; Mayer 1984)

Th is type of morphotectonic structure has also been

observed on the eastern sector of the active Tyrnavos

Fault (Th essaly, central Greece, Caputo 1993; Caputo

et al 2004).

Northeast of the Manastır Fault, there is a

3-km-long fault (i.e the Taşlıburun Fault) at a left -step

confi guration (Figure 1b) Th ese two segments are

connected by a N–S-trending fault Another segment

(i.e the Keçiliköy Fault), 1.5 km long with resistant,

striated, and corrugated fault planes developed

within Mesozoic carbonates of the Bornova Flysch Zone, was mapped northwest of the Taşlıburun Fault Th e main fault planes are characterised by millimetre-scale frictional-wear striae, and metre-scale corrugations are typically underlain by several centimetre- to metre-thick fault gouges preserved within the footwall It is possible that the three left -stepping en échelon segments merge into a single fault plane at seismogenic depths All segments are clearly defi ned by linear escarpments, across which variable reliefs exist (20–400 m) It is notable that the southern segments occur at higher elevations (Figure 3c) Th ey display a persistent zigzag trace with a total length of up to 10 km (Özkaymak & Sözbilir 2008) Based on empirical relationships (Wells & Coppersmith 1994; Pavlides & Caputo 2004), a 10-km-long fault is capable of generating an earthquake with a magnitude of 6.5 Th e length of this segment is similar to the thickness of the seismogenic

layer in the region (e.g., 10 km, Akyol et al 2006).

We mapped several northeast dipping faults between the Manastır Fault and the Paşadeğirmeni Fault Zone with a similar strike (N60°W) Th ey are composed of a series of parallel fault strands, each with a much lower relief of typically 3 m, spread over

a region 1 km wide All cut and deform the upper Pleistocene–lower Holocene Emlakdere Formation, and thus have been active at least until the Late Holocene (Figure 4b)

Fault-1 is closest to the Manastır Fault It cuts and back-tilts the strata of the Emlakdere Formation

Th e vertical off set associated with rotation of a downthrown block around the horizontal axis implies the activation of Fault-1 Fault-2 is indicated

by a discontinuous morphological scarp 1.5 km long running parallel to the trace of the Manastır Fault Fault-3, which can also be traced as a morphological scarp, sinistrally off sets the N–S-trending and north-

fl owing stream along its eastern portion Th ese may be shallow synthetic normal faults caused by refraction of the Manastır Fault Although they may move simultaneously with the Manastır Fault, they merge with it at depth and may even then produce negligible seismic moment

Th e colluvial sediments of the Emlakdere Formation are likely to have been deposited at dips

of about 5–10° northwards but now dip at angles of

about 50–60° southwards (Figures 4 & 5a–c)

Back-tilting of the down-thrown block towards the fault

scarp was observed along the quarry road, suggesting

the listric geometry of the Manastır Fault Listric

faults, fl attening at shallow depth, are common

features in extensional tectonic environments Th ey

may produce repeated surface displacements during

strong earthquakes, thus generating typical

tectonic-gravitational landforms such as secondary

fault-bounded tilted blocks (Dramis & Blumetti 2005)

Stratigraphy and Facies Analysis of the Quaternary

Deposits

While Neogene tectonic evolution of the West

Anatolian extensional province has been well studied

(Emre & Sözbilir 1997; Koçyiğit et al 1999; Bozkurt

2000; Sözbilir 2001, 2002; Bozkurt & Sözbilir 2004;

Çift çi & Bozkurt 2008, 2009, 2010), little information

is available on its Quaternary evolution (Hakyemez et

al 1999; Bozkurt & Sözbilir 2006; Özkaymak & Sözbilir

2008) Th e indicators of Quaternary deformation are

mainly located in the studied area Structural analysis

of normal faults off setting Quaternary sediments was

based on the study of striated fault planes and off sets

of the upper Pleistocene–lower Holocene Emlakdere

Formation (Özkaymak & Sözbilir 2008) Th ese types

of structures are scarce and concentrated mainly in

the western end of the MFZ, between the villages of

Gürle and Emlakdere (Figure 4)

Th e region in which the study area is located

contains four unconformity-bounded units: the

upper Cretaceous–Palaeogene Bornova Flysch

Zone, a Miocene volcano-sedimentary unit, the

upper Pleistocene–lower Holocene age Emlakdere

Formation, and upper Holocene modern graben fi ll

(Figure 4)

Th e Emlakdere Formation

Back-tilted colluvial and alluvial sediments in the

western part of the MFZ were mapped and named

the Emlakdere Formation by Özkaymak & Sözbilir

(2008) and dated as late Pleistocene–early Holocene

in the present study Th e Emlakdere Formation

comprises unsorted crudely stratifi ed gravel and

cobble-pebble conglomerate alternating with several

palaeosol layers (Figures 5a, b & 6) Th e unit is

overlain with an angular unconformity by upper Holocene colluvial/alluvial fans (Figure 5c)

In an attempt to obtain a representative section of overall upper Pleistocene–lower Holocene debris-fl ow activity within the area, two sections were measured along the quarry road (Figure 6)

type-Th ey proved to cut approximately the full thickness

of the Emlakdere succession Individual sediment layers were characterised in terms of matrix and clast characteristics, grain-size, grading, sediment structures, and the nature of contacts between

adjacent layers (Harms et al 1975; Collinson &

Th omson 1982; Blikra & Nemec 1998; Sletten & Blikra 2007) In each profi le, we identifi ed the main units and morphological features; we also measured soil colour using the Munsell® colour book (Munsell Color Company 1994) Th e characteristics and interpretation of the main sedimentary facies are outlined below and illustrated in two measured sediment logs (Figures 6 & 7)

Th e observed sedimentary facies can be diff erentiated into four major groups: rock fall, debris fall, debris fl ow, and palaeosol Th e diagnostic sedimentological characteristics of the main sediment types are shown in Figure 7

Debris Flow– Th is facies consists of tabular beds with large fl oating clasts Large clasts are mainly aligned downfl ow Most of the beds show inverse grading and are characterised by a matrix-rich to clast-supported sandy-muddy matrix including boulders up to 212 cm in diameter (Figures 7 & 8a) Some beds are lenticular with imbricate or more complex stacking Th ese deposits are interpreted as proximal to distal facies of high- to low-viscosity debris fl ows (cf Blikra & Nemec 1998)

Debris Fall– Th is facies is characterised by immature to mature debris including subangular

to subrounded clasts (Figures 7 & 8b) Massive to upward-fi ning and typically clast-supported units are common Deposits are oft en infi lled with sandy mud, although some openwork structure is also visible

Rock Fall– Th is consists of highly immature debris, mainly angular clasts in a pebbly to sandy-muddy matrix (Figures 7 & 8c) Massive to normally-graded and clast-supported units showing openwork structures are common (Figure 8d) Clasts in such units are up to 2 macross Some rock-fall units

72

29 28

723 Açarlıktepe Hill Yassımeşe Ridge

2

1

TaF

Ta F

PFZPFZ

33 10

18

52 18

12

S1 S2

61

T1 T2

measured stratigraphic section (S1 and S2)

normal fault scarp

strike-slip fault

volcanic rocks

250 m 0

late Holocene late Pleistocene-early Holocene

Neogene

volcano-sedimentary rocks Neogene

late Cretaceous Paleocene –

Figure 4 (a) Detailed geological map of the study area showing NW–SE-trending active faults and

location of trench sites on the southern branch of the PFZ (see Figure 1b for map location)

Abbreviations PFZ, MaF, TaF, GFZ, T1, T2, S1, and S2 refer to the Paşadeğirmeni Fault

Zone, Manastır Fault, Taşlıburun Fault, and Gürle Fault Zone, Trench-1, Trench-2,

stratigraphic section 1, and stratigraphic section 2, respectively (b) Geological cross

section showing stratigraphic and structural relationships of the units Note that the

off set of Quaternary deposits by several instances of synthetic Holocene faulting in the

hanging wall of the Manastır Fault is the most direct evidence for their activity.

exhibit a fl ow-parallel orientation a(p), indicating

sliding fabric Bed thickness is typically 70–200

cm Contacts between units are generally sharp

but apparently conformable, indicating little or no

erosion of underlying units Th e colour of the matrix varies from light-yellowish brown (10YR 6/4 in Munsell colour value) to reddish yellow (7.5YR 6/6), similar to the underlying organic soils

dip of the layersunconformity

a

b

c

N S

S

NW SE

N

PS3 PS6

PS6 PS10

PS5 PS4

PS2

PS12

Figure 5 Field views showing (a) lower, (b) middle, and (c) upper part of the Emlakdere Formation Note the steeply dipping

lower part and gently dipping upper part of the bedding.

9199±67 14270±360

19030±560

54

173

133 91

93 95 97 99

105

103

101

107 109 111 113 115 117 119

PS3 PS4

PS5

PS6

PS7 PS8

PS9 PS10 PS11

PS12 PS13

PS14

125 127 129 131

135 137 139 141 143 145 147 149 151 153 155 157 159 161 163 165 167 169 171

175 177 179 181 183 185 187 0

56 58 60 62 64

fining-upward sequence coarsening-upward sequence

debrisflow rockfall debrisfall palaeosol

Figure 6 Stratigraphic sections of the Emlakdere Formation measured in detail See Figure 4 for section locations (S1 and

S2) Note that locations of the dated palaeosol are also indicated as 14 C age data PS- palaeosol.

openwork openwork

scattered clasts

fresh rock debris

varied runout

resedimented gravel

upslope fining

lobate or 'patchy accumulations of debris;

scattered large outrunners

low-viscosity/watery debrisflow

tabular beds large floating clasts

subangular to subrounded clasts boulder to sand size grade, clast-supported and commonly openwork, with pebbly to sandy-muddy infill at the top Deposits often infilled with sandy mud and redeposited soil material

matrix-rich to supported.

clast-sandy/muddy matrix.

common coarse tail inverse grading and outsized cobbles or boulders

upward coarsening

weathered bedrock older debrisflowsediments

boulders and large cobbles often shown rolling fabric,a(t) or a(t)b(i).

many large clasts upslope show sliding fabric a(p).But a disordery adjustment fabric predominates;

shear fabric a(p) often typifies the avalanche’s overriding tail, when evolved in to grainflow

upper-slope colluvium

common rolling fabric a(t) in the frontal and top part of the debrisflow head; common shear fabric a(p) or a(p)a(i)

in the flow’s tail

clast-supported, bouldery to cobby heads and clast to matrix-supported, pebbly upslope tails , common normal grading

parallel imbricate beds

lenticular beds with imbricate or more complex stacking

rockfall/debrisfall

high-viscosity debrisflow

common carbonate-rich slope wash material derived from weathering limestone bedrock AVALANCHES

Figure 7 Diagnostic sedimentological features of the main sedimentary facies observed in the measured stratigraphic sections of the

Upper Pleistocene–Lower Holocene Emlakdere Formation (compiled from Blikra & Nemec 1998).

a

S

ff c

b

d N PS3

dip of the layer

212 cm

Figure 8f

Figure 8 Field photographs of the Emlakdere Formation, showing colluvial facies and depositional processes (a) Debris-fl ow deposits

Immature cobbles and boulders are randomly distributed within the sandy muddy matrix, the largest one 212 cm long (b) sedimented debris-fall deposits consist of relatively mature subrounded to rounded gravels (c) Close-up view of the rock-fall deposit composed of boulders and large cobbles Clasts are angular, very immature, and show random orientation (d) Close-

Re-up view of the clast-sRe-upported lenticular bed within debris-fl ow deposits Note that the non-stratifi ed openwork gravels show

multimodal grain-size distributions (e) View of the steeply dipping section of the Emlakdere Formation showing debris-fl ow units alternating with a thick palaeosol (f) Close-up view of PS3 palaeosol level given in Figure 8e Note that the upper levels

of the palaeosol have vertical/subvertical cracks fi lled by carbonate-rich sediments.