www.elsevier.com/locate/enggeo

Engineering Geology 7

Landslide inventory of northwestern Anatolia, Turkey

Tamer Y. Dumana, Tolga Canb,*, Omer Emrea, Mustafa Kecera, Ahmet Dogana,

Xerafettin AteYa, Serap Durmaza

aGeneral Directorate of Mineral Research and Exploration, Department of Geological Research, 06520 Ankara, TurkeybCukurova University, Department of Geological Engineering, 01330 Balcali, Adana, Turkey

Received 10 February 2004; accepted 26 August 2004

Available online 12 October 2004

Abstract

Turkey is heavily exposed to natural hazards such as earthquakes, landslides and floods. The total loss caused by landslides

in terms of affected buildings, in a period of 35 years between 1959 and 1994, constitutes 27% of the entire loss from all natural

hazards and is second after earthquakes. There are no other available data on either direct or indirect losses due to landslides on

a national scale.

The General Directorate of Mineral Research and Exploration (MTA) started the dTurkish Landslide Inventory Mapping

ProjectT in 1997 to improve understanding of regional and national landslide processes. The purpose of the project is to establish

landslide inventory maps at medium (1:25,000), regional (1:100,000) and national (1:500,000) scales. Existing landslides are

mapped on 1:25,000 scale topographic base maps by interpretation of aerial photographs and field investigations. The base

maps are then digitized and stored in a geographic information system (GIS) database by the Geological Research Department

of MTA. Hence, regional- and national-scale landslide maps will be available as well, as the work progresses. Landslides are

classified as fall, topple, slide and flow and are broadly characterized as active or inactive. The landslides are also classified

according to their relative depths, as shallow (depth b 5 m) and deep-seated (depth N 5 m). The present paper will attempt to

describe the project standards and its application to the area of 1:500,000 scale Zonguldak quadrangle. The study area extends

to 39,081 km2, and 7.1% of the area was found to be affected by landslides. A total 10,007 landslides (392 shallow-seated, 8020

deep-seated active and 1595 deep-seated inactive) were mapped in the area covering 2768 km2. Cretaceous flysch, Paleocene–

Eocene flysch and Paleocene–Middle Miocene volcanics are the most landslide-prone units and constitute 27.8%, 29.9% and

7.2% of the all landslides, respectively.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Landslide; Landslide inventory mapping; Turkey; Zonguldak

0013-7952/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.enggeo.2004.08.005

* Corresponding Author. Tel.: +90 322 3387058; fax: +90 322

3386126.

E-mail addresses: tduman@mta.gov.tr (T.Y. Duman)8

tolgacan@cukurova.edu.tr (T. Can)8 emre@mta.gov.tr (O. Emre).

1. Introduction

Landslides, either alone or in association with

the earthquakes, volcanic eruptions, wildfires and

major rainstorms that may trigger landslides, are a

7 (2005) 99–114

Fig. 1. Location map of the study area.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114100

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114 101

major cause of loss of life, injury and property

damage around the world (Cruden and Fell, 1997).

In many countries, socioeconomic losses due to

landslides are great and apparently growing as

human development expands into unstable hillslope

areas under the pressures of increasing populations

(Schuster, 1996). A reliable landslide inventory

defining the type and activity of all landslides, as

well as their spatial distribution, is essential before

any analysis of the occurrence of landslides and

their relationship to environmental conditions under-

taken (Soeters and Van Westen, 1996). However,

landslide inventories are not yet very common,

despite the ease with which they are prepared and

their immediateness (Guzzetti et al., 2000). Inven-

tory maps are available in only a few countries and

mostly for limited areas (Brabb and Harrod, 1989;

Brabb, 1993).

Turkey is exposed to natural hazards such as

earthquakes, landslides and floods. Loss of buildings

due to landslides between 1959 and 1994 constitutes

27% of the entire loss due to all natural hazards and is

second after earthquakes (IldVr, 1995). There are no

other available data on other direct or indirect impact

of landslides at the national scale. The bTurkishLandslide Inventory Mapping ProjectQ was started by

the Natural Hazards and Environmental Geology

division of the General Directorate of Mineral

Research and Exploration (MTA) in 1997 to achieve

a better understanding of the regional and national

landslide processes.

In this paper, we attempt to describe the project

standards and its application to the area of the

1:500,000 scale Zonguldak quadrangle in northern

Turkey (Fig. 1). The Zonguldak quadrangle, cover-

ing an area of 39,081 km2, is located into three

geographic region of Turkey, namely, the western

Black Sea to the north, the central Anatolia to the

southeast and the Marmara to the west (Fig. 1). The

study area presents diverse geological, tectonic,

geomorphologic and climatic conditions which

control the extent and geographical distribution of

landslides. Landslides of different type and activity

cover 7.1% of the entire region. According to the

geological setting, landslides are most abundant in

flysch rock units. These units cover 28% of the

study area and encompass 58% of all the landslides

in area.

2. Settings of the area

2.1. Geological setting

The study area is located in the western Pontides,

composed of the Istanbul–Zonguldak zone, the

Armutlu–OvacVk zone and the Sakarya continent

(Fig. 2). The basement of the Istanbul–Zonguldak

zone consists of four different rock series separated

by regional unconformities. The series from bottom to

top starts with a Paleozoic sedimentary sequence

composing of continental conglomerates, arkosic

sandstone and marine clastics, Triassic thick terrestrial

unit comprising meandering river and flood plain

sediments, Middle Jurassic clastic units consisting of

sandstone, siltstone and siliciclastic turbidits and an

Upper Jurassic–Lower Cretaceous homogeneous plat-

form carbonate sequence (Gorur et al., 1997; Dean et

al., 1997; Tuysuz, 1999). There are two Cretaceous

sedimentary basins in this zone: the Zonguldak and

the Ulus basins. The Zonguldak basin fill comprises

clastics, carbonates and volcanics rocks, while the

Ulus basin fill consists of flysch sediments as

conglomerates, sandstone, siltstone and claystone

alternation. Latest Cretaceous–Eocene flysch sedi-

ments locate conformably on the Zonguldak basin.

The basement of the Sakarya zone is composed of

two distinctly different metamorphic associations,

namely, the Uludag and Yenisehir groups (YVlmaz et

al., 1997). The Uludag Group is composed of high-

grade schist, gneisses, amphibolites and intruding

granitic pluton of Carboniferous age, while the

Yenisehir Group consists of metaophiolite and meta-

morphosed volcanic and sedimentary units. On the

top of the two metamorphic associations, transgres-

sive sequence starts with clastics and passes upward

into platform carbonates (Yigitbas et al., 1999). A

flysch sequence was formed in the northern areas

during the Upper Cretaceous period (YVlmaz et al.,

1995). The flysch is replaced gradually upwards by

shallow-marine sandstones and reefal limestone. The

Neogene age Galatean Volcanic province has been

emplaced onto units of the Sakarya continent. The

Armutlu–OvacVk zone is an E–W-trending zone

squeezed between the Istanbul–Zonguldak zone and

the Sakarya continent (Yigitbas et al., 1999). This

zone comprises a tectonic mosaic consisting of

different tectonostratigraphic units. Pliocene and

Fig. 2. (a) Major tectonic units (from Yigitbas et al., 1999) and (b) simplified geological map (after MTA, 2003) of the study area.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114102

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114 103

younger sediments unconformably overlie the older

units in the study area.

2.2. Tectonics and seismicity

The Anatolian plate is being squeezed westward

away from the collision zone between the Arab–

African and Eurasian plates along the north Anatolian

and east Anatolian fault systems that formed in the

collision (Sengor et al., 1985). The north Anatolian

fault system (NAFS) is a 1600-km long, right-lateral

strike–slip, active transform fault running along the

northern Anatolia in the E–W direction (Fig. 3). In the

western part of the study area, the fault zone

comprises the northern and southern strands in

Fig. 3. Major faults (modified from Xaroglu et al., 1992) and earthquake epi

in the study area.

between Bolu and the Sea of Marmara and includes

the Hendek and Cilimli faults that are situated north of

the Sakarya and Duzce basins (Fig. 3) (Emre et al.,

1998; Kocyigit et al., 1999).

During the last century, the NAFS has produced

earthquakes along different sections in a systematic

manner. Beginning with the 1939 Erzincan earthquake

(M =7.9), which produced about 350 km of ground

rupture, the NAFS was ruptured by nine moderate to

large earthquakes (M N 6.7) and formed more than

1000 km surface rupture along the fault (Bozkurt,

2001). Five of them [February 1944, Bolu–Gerede

(M =7.3); May 1957, Abant (M =7.0); July 1967,

Mudurnu Valley (M =7.1); August 1999, Kocaeli

(M =7.4); and November 1999, Duzce (M =7.2)]

centers withMWN5 (data adapted from http://www.koeri.boun.edu.tr)

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114104

occurred in the study area. The Orta earthquake

(M =6.0) occurred at the eastern boundary of the

study area on June 6, 2000. Although the area is

affected by several large earthquakes, historical

information on earthquake-induced landslides for the

region and even for the other parts of Turkey is not

present. However, some of the landslides in the study

area, particularly along the NAFS, might have been

triggered by the historical earthquakes.

2.3. Geomorphologic setting

Mountain belts and plateaus mainly represent the

regional morphology of the study area besides the

tectonic depressions developed along the NAFS (Fig.

4). Considering the major landforms, the NAFS

separates the region as the southern and the northern

divisions. Major landforms between the NAFS and

the Black Sea coast extend into the NE–SW direction

that is parallel to the major fold axis and thrusts.

Clastics and carbonate rocks of Paleozoic and flysch

Fig. 4. Shaded relief map

sequence of Paleocene–Eocene formed the folded

mountains, along the Black Sea coast. Cuestas,

developed by the erosion of the units on the flanks

of the anticlines and synclines, are the common

macro-morphological landforms. The area is deeply

incised by dense drainage network and has rough

topography. Hillsides are the dominant landforms on

the folded mountains and represent relatively higher

reliefs. Sakarya, Melen, Filyos and Bartin are the

principal rivers traversing the folded mountain belt

and discharging into the Black Sea. Deep canyons

along the rivers reach up to 1000 m of relative heights

in some places. Landslides in the study area are more

abundant along the folded mountain belt.

As to the southern part of the study area, it can be

separated into two major landforms. Strata volcano and

scattered single volcanic cones constitute high moun-

tains, and volcano sedimentary units form the plateaus

in the Galatean volcanic province. Generally, lavas are

the uppermost strata on the plateaus. Landslides are

more common in the volcano-sedimentary rocks

of the study area.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114 105

beneath the volcanic units along the deep valleys.

Another folded mountain belt, trending in the E–W

direction, is situated at the southwest part of the area. In

general, the region is represented by the plateau named

Mudurnu–Yenipazar, incised by the tributaries of the

Sakarya and Mudurnu Rivers. Cuestas are the rough-

nesses rising on the erosional surfaces formed after

erosion of the E–W-trending folds.

Tectonic landforms are distinctive along the NAFS

in the study area. Linear valleys, throughs and pull-

apart basins are the macro-morphologic features

developed in the strike–slip morphology. Offsets

alternate from several meters to 60–70 km. (Xengor,

1979, Hubert-Ferrari et al., 2002).

2.4. Climate

There are two main climatic regions in the study

area, namely, the Black Sea climatic region to the

north and the continental inner Anatolian climatic

region to the southeast. The Black Sea climatic region

covers the northern part of the Anatolian peninsula,

and its southern boundary follows the upper part of

the southern flanks of the northern Anatolian Moun-

tains extending roughly in the E–W direction. The

elevation between valley floor and upper part of the

mountains attain more than 1000 m. Maritime climate

conditions prevail on the coastal belt of the Black Sea,

and the region receives rainfall throughout the year.

The mean annual precipitation exceeds 1000 mm and

reaches up to 2300 mm in the eastern part of the Black

Sea. The northern slopes of the coastal mountain belt

receive abundant precipitation due to interception of

the fronts coming from the north, and landslides are

more abundant in this region. Precipitation decreases

to 500 mm in the southern part of the region.

Continental semiarid climate prevails in the inner

Anatolian region. The mean annual precipitation

ranges from 400 mm in the plain to 600 mm in the

plateau and mountainous areas. The rainiest period

takes place during the spring, notably in April and

May (Atalay, 2002).

3. Landslide inventory

Vertical black-and-white aerial photographs of

medium scale (1:35,000) and large scale (1:10,000)

were used to identify the landslides. A single set of

2551 large-scale aerial photographs, dated from 1974

to 1976, were interpreted mainly for the north

Anatolian fault zone. A total of 5570 medium-scale

aerial photographs taken between 1940 and 1957 were

used for the rest of the area. As the dates of available

photos were not recent, detailed field checks and

investigations were evaluated. Photo interpretations

were conducted with SOKKISHA MS27 mirror

stereoscopes of 1.8� and 3� magnifications. Land-

slides were manually mapped onto the medium-scale

(1:25,000) topographic maps. Accuracies of landslide

locations obtained by this process are estimated to be

better than 50 m in areas of gentle slopes and to better

than 25 m in areas of steep slopes. This study was

carried out between 1997 and 1998. Eight months of

field studies were conducted during the summer

seasons of 1997 and 1998. The digitized version of

the inventory map was accomplished by the end of

2000. About 12 staff people participated for photo

interpretation and field study, and an additional 3

people accomplished the digitizing processes.

Mass movements were classified according to the

main types of Varnes (1978), i.e., flows, falls and

slides. The landslides are also classified according to

their relative depths, as shallow- (depthb5 m) and

deep-seated (depthN5 m). For simplicity, their activ-

ities are classified into two groups as active and

inactive. Active landslides are defined as those

currently moving, whereas inactive ones are as relict

according to WP/WLI, 1993. Shallow landslides are

classified as active because of their ongoing observed

movements. Onscreen method of digitization is used

for landslide data input and storage in Arc/Info

geographic information system (GIS). The base maps

were scanned with 100 dpi resolution and georefer-

enced to the UTM coordinate system. The total root

mean square (RMS) errors were kept less than 0.005

in. = 0.127 mm which is equivalent to 3.175 m ground

resolution at 1:25,000 scale. Landslides were stored as

polygons and landslide type, and depth and state of

the activity were built in attribute tables.

The Zonguldak quadrangle covers an area of

39,081 km2. A total of 10,007 landslides were

mapped in the area covering 2768 km2 (Fig. 5).

Thus, the average landslide concentration was

found as 0.25 landslides/km2. The minimum land-

slide size included in the inventory is 0.0025 km2.

Fig. 5. Landslide inventory map of the study area with major drainage patterns.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114106

Descriptive statistics on landslides identified in the

area is given in Table 1. The smallest and the

largest landslides were identified in Paleocene–

Eocene flysch unit. The largest landslide covering

76.92 km2 is located on the northern flank of a

large synclinorium extending in the E–W direction

along the Soganli River valley side (Fig. 6). The

relative elevation difference from the valley floor to

the ridge reaches up to 550 m. The monoclinal

sequence in the area is mainly composed of the

Table 1

Statistical summary of the landslides identified in the area

Descriptive

statistics

Shallow

landslide

Deep

landslide

(active)

Deep

landslide

(inactive)

Total

Count 392 8020 1595 10,007

Mean (km2) 0.96 0.18 0.47

Minimum (km2) 0.0049 0.0025 0.0044

Maximum (km2) 10.96 21.95 76.92

Sum (km2) 400 1672 696 2768

alternation of conglomerate, sandstone, claystone

and marl. The strike of the bedding planes is about

E–W in direction with dip angles varying from 88to 158 to the south. As a whole, the landslide was

defined as inactive, but recent reactivations were

also delimited. The type of movement is complex,

but dominant movement is translational which is

mainly controlled by the bedding planes. The

estimated depth of the landslide according to the

topographic cross sections is about 130 m. The

main characteristics and the distribution of land-

slides in relation to the geological units are

summarized in Table 2. Landslides located along

the contact between the two geological units were

not considered during the statistical analysis if more

than 10% of the area passes to the other unit.

About 10% of tolerance was taken arbitrarily

considering the probable accuracy errors of the

geological map. The total excluded landslides by

this process is equivalent to 17% of all landslides.

Cretaceous flysch, Paleocene–Eocene flysch and

Fig. 6. Landslide inventory map for the largest landslide identified in the study area.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114 107

Paleocene–Middle Miocene volcanics are the most

landslide-prone units and constitute 27.8%, 29.9%

and 7.23% of the all landslides, respectively.

3.1. Landslides in Paleocene–Eocene flysch

The Paleocene–Eocene flysch can be divided into

four facies according to sedimentological character-

istics. Turbiditic sandstone facies, consisting of

conglomerate, sandstone, and shale alternations,

forms the bottom facies. This facies is overlain by

volcanoclastic facies, which consists of lithic tuff and

tuff breccia with andesitic composition and volcano-

clastic sandstone–siltstone. The third facies is charac-

terized by crystal and vitric tuff and thinner than the

others. The last facies of the formation is a shallow-

marine facies of Middle Eocene age consisting of

mainly sandstone claystone alternation (Ilgar and

Xahbaz, 1997). The thinly and moderately thick

bedding planes are extensive and persistent types of

discontinuity. The thickness of the colluvium or

residual silty clayey to clayey soil reaches up to 20

m, particularly at the toe of hillsides. These units

present gentle morphology in the rugged and dis-

sected topography of the region. The minimum and

maximum altitudes, above sea level, change between

10 and 1000 m, with a mean value of 350 m. The

slopes are lower than 208 in general. According to the

deposition conditions, the slope gradients are higher

around the boundary between underlying units.

Because of their low-relief characteristics, the unit is

intersected by several primaries river. The ground-

water elevation is mostly close to the ground surfaces

because of the wet climatic conditions and the

alternation of permeable and impermeable rocks.

The unit covers an area of 4915 km2, 12.6% of the

study area. Covering 826 km2, 2286 landslides were

identified, of which 179 are shallow and the others are

deep-seated. The two principal types of landslide

movements are slide and flow. In between the slides,

rotational (Fig. 7a) or complex (Fig. 7b) landslides are

more common and have occurred where alternation of

thinly bedded sandstone and extremely weak to weak

claystone and siltstone layers exist. Deep landslides

concentrate along the southeastern parts of the unit

because of relatively steeper slopes (N108) and higher

Table 2

Distribution of landslides based on geological units

Rock type Geological unit Unit area

(km2)

Shallow landslides Deep landslides Lands

density

in the

unit (%)

Overall

landslide

density

(%)

Area (km2) Active landslide area (km2) Inactive andslide area (km2)

na Mean Maximum Minimum na Mean Maximum Minimum na ean Maximum Minimum

Sedimentary Quaternary–Pleistocene

(undifferentiated)

3942 23.6 51.6 19.3 2.4 3.41

2 0.25 0.30 0.20 116 0.04 0.20 0.005 19 .08 0.31 0.005

Pliocene continental

clastics

1531 1.9 66.4 17.5 5.6 3.10

8 0.34 0.61 0.078 275 0.06 0.72 0.005 32 .23 0.79 0.009

Pliocene–Oligocene

evaporitic rock

1151 1.8 15.7 6.5 2.1 0.87

12 0.17 0.56 0.039 113 0.10 1.87 0.004 36 .13 0.71 0.017

Lower–Middle Miocene

continental clastics rocks

1233 – 20.5 35.7 4.6 2.03

– – – – 101 0.11 1.81 0.003 41 .70 8.33 0.040

Lower Eocene–Upper

Miocene neritic limestone

619 0.8 31.7 13.8 7.5 1.67

– – – – 100 0.09 1.15 0.008 32 .16 1.04 0.027

Middle–Upper Eocene cont.

clastics and carbonates

210 – 22.6 12.6 16.8 1.27

– – – – 89 0.12 2.52 0.009 12 .20 0.46 0.015

Paleocene–Middle Eocene

clastics and carbonates

4915 253.2 380.0 193.3 16.8 29.86

179 0.92 10.96 0.005 1817 0.17 4.78 0.003 290 .54 76.92 0.008

Upper Cretaceous–Eocene

Clastic carbonates

3334 33.9 105.2 45.2 5.5 6.66

34 0.58 4.46 0.036 657 0.10 2.67 0.004 57 .45 2.42 0.028

Upper Cretaceous volcanic

and sedimentary rocks

1124 11.3 24.0 2.6 3.4 1.37

21 0.34 1.09 0.005 171 0.11 1.10 0.005 6 .20 0.71 0.030

Cretaceous clastics

and carbonates

5979 36.4 613.1 119.0 12.9 27.77

12 1.29 6.05 0.048 2,136 0.20 11.70 0.003 329 .32 7.50 0.015

T.Y.Dumanet

al./Engineerin

gGeology77(2005)99–114

108

l

M

0

0

0

0

0

0

0

0

0

0

Sedimentary Middle Jurassic–

Late Cretaceous

neritic pelagic limestones

1870 2.8 39.2 29.9 3.8 2.6

– – – – 127 0.12 1.36 0.009 60 0.28 2.21 0.017

Lower–Middle Jurassic,

volcanic and sedimentary,

carbonates and clastics

315 3.3 25.2 12.2 12.9 1.47

– – – – 61 0.08 0.46 0.009 17 0.57 3.80 0.026

Ordovician Triassic

Cont. clastics,

carbonates

2239 23.9 114.0 7.1 6.5 5.24

8 1.22 2.49 0.294 336 0.17 3.56 0.003 30 0.23 3.05 0.004

Magmatic Paleocene–Middle

Miocene volcanic and

pyroclastics

6132 – 88.0 112.0 3.3 7.23

– – – – 321 0.15 3.38 0.006 153 0.59 13.34 0.019

Upper Cretaceous–

Upper Miocene basalt,

andesite

920 4.9 28.4 6.6 4.3 1.44

6 0.54 1.38 0.103 199 0.07 0.94 0.006 24 0.30 2.59 0.014

Upper Cretaceous

ophiolites

296 – 12.2 31.4 14.8 1.58

– – – – 36 0.22 1.14 0.012 32 0.18 0.94 0.024

Precambrian–Paleocene

granitoid

1299 – 0.9 3.9 3.5 0.6 0.30

3 0.26 0.39 0.058 15 0.17 1.62 0.009 9 0.15 0.49 0.021

Metamorphic Upper Cretaceous

metagabbro, amfibolite,

etc.

141 – 2.7 0.2 2.1 0.10

– – – – 12 0.16 0.56 0.022 – – – –

Precambrian–Upper

Cretaceous gneiss, schist

1739 1.3 24.3 26.9 3.0 1.90

2 0.19 0.20 0.185 78 0.20 6.80 0.013 56 0.21 1.68 0.004

Upper Paleozoic–

Cretaceouous marble

92 – 3.2 0.6 4.2 0.14

– – – – – – – – – – – –

Total 39,081 400 1672 696 100

a Number of landslides of which more than 90% of the landslide area located in the same unit.

T.Y.Dumanet

al./Engineerin

gGeology77(2005)99–114

109

Fig. 7. Landslides in Eocene flysch unit: (a) rotational slide, (b) deep complex slide, (c) creep and (d) shallow complex slide.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114110

altitudes. High groundwater conditions and alternation

of very weak clay–claystone and siltstone units with

relatively thicker sandstone layers cause translational

failure where appropriate conditions exist (i.e., slope

angle, outslope bedding conditions, excessive pore

water pressure, and low shear strength parameters of

clayey units). Colluvium on slightly inclined slopes

and undrained morphologies are 4–5 m thick. In these

areas, creep (Fig. 7c) and shallow landslides prevail

(Fig. 7d). These types of movements are characteristic

on slopes lower than 108. Earth and debris flows are

mainly observed in the slide masses and in preexisting

drainage paths. As the scarps of the flows heal

quickly, because of wet climatic conditions, they can

be identified and mapped only for 1 or 2 years.

3.2. Landslides in Cretaceous flysch

This unit, which has the second highest landslide

concentration, crops out both in the western Pontides

and in Sakarya continent zones. In the Sakarya basin,

Cretaceous flysch consists of volcanoclastic sediments

at the base, grading vertically into alternation of

sandstone and shale. The middle part of the unit is

represented by pelagic clayey limestone, biomictitic

limestone with shale, sandstone and conglomerate

alternation. The upper part of the unit comprises

sandstone, claystone, marl and limestone alternation

(AltVner et al., 1991). The unit covers an area of 5979

km2, 15% of the entire study area. A total of 2477

landslides were identified, covering 768 km2, of which

80% are deep-seated. Slides and flows are the two main

type of mass movements. The geographical distribu-

tion of landslides is mainly controlled by facies

changes within the flysches. The landslides are not

located in coarse-grained fan, channel deposits and

limestone layers of the unit. Deeper layers represented

by clastics as mudstone, claystone and sandstone

alternation exhibit a high landslide abundance. These

layers have low shear strength properties, and bedding

planes are generally thinly bedded. Slides are mostly

circular, and they develop independently of bedding

orientation because of the weak properties of the rock

mass (Fig. 8a). The second most common type of

failure is flow, mostly earth and debris flow in the

topsoils or in highly weathered alteration zones (Fig. 8b

and c). Debris flows are mainly observed on steep

slopes, whereas earth flows occurred on gentles slopes.

Fig. 8. Landslides in Cretaceous flysch unit: (a) rotational slide, (b) earth flow and (c) debris flow.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114 111

3.3. Landslides in Paleocene–Middle Miocene

volcanics

The Galatean Volcanic Province (GVP) is a

Neogene volcanic belt extending for some 250 km

along the northern margin of the Anatolian block

(Toprak et al., 1996). The northern margin of the

province is sited at the active boundary defined by

the NAFS. The Miocene volcanics cover an area of

6132 km2, which is 16% of the entire study area.

Landslides, which are all deep-seated, cover 6.8% of

the unit. The deep-seated landslides are mainly

observed where thick tuff and agglomerate layers

are predominant (Fig. 9a). Holocene age drainage

developed on the slide masses indicates their

continuous activity from the Late Pleistocene to

recent time. The landslides are most abundant on the

E–NE and SW flanks of the volcanic province.

Retrogressive type failures occurred on north-facing

slopes in the vicinity of the NAFS where alternation

of lavas and pyroclastics layers rest over the melange

unit. The toes of the slides are more active because

of fluvial erosion processes (Fig. 9b).

3.4. Recent landslide events

Heavy precipitation and large earthquakes are

known as major landslide-triggering factors. An

extreme rainfall and two large and one moderate

earthquake were experienced in the study area from

the beginning of the project. Due to the heavy

precipitation on 19–21 May 1998, flooding and

landslide events occurred in the western Black Sea

region mainly comprising the cities of Bolu, Zon-

guldak, Kastamonu and BartVn. This meteorological

event caused 10 deaths and extensive damage to

both public and private property and cost social and

economic disruption. According to the official

information, total economic cost was estimated as

500 million USD.

Thousands of shallow landslides of earth and

debris flow in character occurred particularly in flysch

units. These units presented already abundant land-

slide concentrations and the most landslide-prone

units in the area studied. Many landslide reactivated

in the area, and the largest landslide triggered by this

meteorological event was about 0.15 km2.

Fig. 9. Landslides in Miocene volcanics: (a) rotational slide and (b)

complex landslide.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114112

The western part of the study area heavily suffered

from the Izmit and Duzce earthquakes; more than

20,000 people were killed, and over 100,000 people

were injured and/or lost their homes and property. The

earthquakes triggered and/or reactivated many land-

slides in the region (Emre et al., 1999; Aydan and

Ulusay, 2002; Duman et al., 2003). Since the Izmit

earthquake occurred in the dry summer season, the

landslides were mainly observed along the lake, sea

and river banks. Several lateral spreadings occurred

along the Sakarya River and Sapanca Lake. A total of

16 shallow landslides occurred due to the earthquake,

along the tectonic valley of Karadere, extending

parallel to the main fault in the E–W direction. In

this region, particularly on the north-facing slopes

along the fault zone, landslides were abundant, and

the area of the largest landslide reached up to 1.4 km2.

Some of the landslides were reactivated along the

fault zone in and outside of the study area. Duzce

earthquake occurred on the Duzce fault which forms a

boundary between the Duzce plain and AlmacVk

tectonic block. Before the earthquake, 181 landslides

were determined along the tectonic boundary during

the inventory studies. The minimum and the largest

landslides identified in this zone were 0.004 and 7.5

km2, respectively. The field observations made after

earthquakes on previously mapped landslides showed

that the shaking slightly reactivated most of the

landslides ranging from several centimeters up to 1

m of movement. A total of five earthquake-induced

shallow landslides were identified closed to the main

rupture. One landslide (0.002 km2) occurred on the

embankment of the main highway at Bolu Mountain

Crossing and caused a shutdown in traffic for 2 days.

The others occurred on weathered granitic and clastics

rock in the sheared zone of the fault.

On 6 June 2000, a moderate earthquake (Mw =6.0)

occurred on the antithetic branch of NAFS, around

town of Orta (Emre et al., 2001). About 3 people died,

200 people were injured, and 4842 structures (unrein-

forced, single- to two-story stone and/or adobe

masonry with mud mortar) were severely damaged

by the earthquake. The volcanic and volcano-sedi-

mentary rock units of the Galatean Volcanic Province

crop out in the region. The majority of the damages

were observed on the masonry dwellings of the rural

settlements, which were mainly situated on the land-

slide masses. Along the Orta fault and near the

vicinity, 152 landslides were identified before the

earthquake, covering 29 km2 ranging from a mini-

mum of 0.004 km2 to a maximum of 2.3 km2.

According to the field studies, four earthquake-

induced shallow landslides were identified besides

several rock fall events on lava cornices with block

size of lower than 1 m3. The earthquake reactivated

most of the previously identified landslides up to 2 m

of displacement. Some of the road embankments,

aligning through the toe of landslides, were also

damaged due to the reactivation of landslides.

4. Conclusions

The inventory needs for the landslide hazard

assessment is still lacking in Turkey. Reliable inven-

tory data has primary importance and influence for any

land use planning procedure, particularly in early

stages and for subsequent site evaluation processes.

T.Y. Duman et al. / Engineering Geology 77 (2005) 99–114 113

The inventory maps produced by this project will

compensate for the basic deficiencies on the regional

and national landslide processes. The landslide inven-

tory map for the 1:500,000 scale Zonguldak quad-

rangle is presented in this article. In addition to the

available facilities, the total cost of the operation,

including the human and technical resources used for

this study, is about US$190,000. The study area

extended to 39,081 km2, and 7.1% of the area was

found to be affected by landslides. Diverse geological,

tectonic, geomorphologic and climatic conditions

control the extent and geographical distribution of

landslides. According to the geological setting, land-

slides are most abundant in Cretaceous and Paleocene–

Eocene flysch units. These units crop out in 28% of the

study area and host 58% of the mapped landslides.

Investigations completed after the 1999 Izmit and

Kocaeli and the 2000 Orta earthquakes indicate that

seismic activity related to the NAFS triggered and/or

reactivated some of the landslides. Due to the lack of

the historical data, additional research is needed to

identify earthquake-induced landslides in the study

area. As the northern slopes of the Black Sea coastal

belt mountains receive high precipitation, landslide

density is higher in this region. As all the data are

digitized and stored in GIS database, this will provide

the basic input needed to generate the regional

landslide susceptibility assessments.

Acknowledgement

This work is done as a part of dThe Turkish

Landslide Inventory Mapping ProjectT supported by

the General Directorate of Mineral Research and

Exploration (MTA). The authors gratefully acknowl-

edge MTA for the support provided.

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