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te GIS BASED NATURAL DISASTER MAPPING: A CASE STUDY
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O. Avsar **, Z. Duran *, D. Z. Seker ?, M. Hisir?, M. Shrestha ^
* ITU, Civil Engineering Faculty, 80626 Maslak Istanbul, Turkey — (avsara, hisirm)@yahoo.com, (duranza, seker)@itu.edu.tr
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a River Basin Research Center, Gifu University 1-1, Yanagido, Gifu-city 501-1193, Japan - madhu@ina.janis.or.jp
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; KEY WORDS: Landslide, Geology, Geo-referenced, Digital Elevation Model, Climate, Water, Block
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| ABSTRACT:
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Sebinkarahisar Township which has been selected as study area is located between Black Sea and Central Anatolian Regions. Not
; only geological characters but also social life in the township had been affected by these two regions. History of the settlements goes
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ih back to early Hittite period. Even it was a province in the first yegrs of Turkish Republic, today it is a township belongs to Giresun
S province. Landslide is one of the most effective natural disasters in the region. Due to wrong decisions of local authorities caused lots
of damage, during the last two decades. Firmly some part of the city, which has the highest landslide risk, is prohibited for new
ih settlement, and some studies (still at beginning level) had been carried out. In this study, morphology, geology, land cover, slope
t inclination, elevation of the region is investigated. 1:25000 standard topographic and 1:25000 standard geological maps are scanned
P and referenced geographically by using Topol software. Contours, settlements, roads, meadows, and forests are digitised from the
geo-referenced topographic map and different geological formations are digitised from the geo-referenced geological map. These
layers are saved as blocks. By extrapolating method, the third dimensions of these blocks are reedited from the contours using
QuickSurf module of AutoCad software. These blocks are added to ArcView software and digital elevation model is produced. Also
the reasons of the occurred landslides are investigated and they are added to ArcView software. Finally the region classified by the
amount of their potential landslide risks and risk map is produced. The aim of this study is: producing a landslide risk map and giving
A some precautions before the planning of the settlement.
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> 1. INTRODUCTION (earthquakes), artificial (explosions for road and mine
constructions) vibrations, rain dose, fountains and churn waters
Landslide is defined as a slide of a large mass of dirt and rock are the other effects. (Tarhan, 1991)
down a mountain or cliff. Landslide is the exterior and .
downward movement of the natural rocks, every sort of soil and According to researches; landslides are caused by 9642 water
a | artificial filling. In another words, the movements of the masses effects, 26 % excavations, 26 % dissociation, 4 94 changing of
c | on the slope sides by the grounds. Usage of industrial, plant cover and 2 % other effects. When these effects are
d agricultural and settlement areas causes some geological events. considered together, the numbers on table | are appeared.
| Landslides are examples of these geological events. Naturally
occurred landslides may cause lost of lives and wealth and also Causes Percentage
" communication and transportation interruptions. Therefore; Dissociation 3
stages of landslide constitutions and causes should be
S, Water 9
researched. =
Excavation 11
d In this study, the occurred landslides in Sebinkarahisar Water + Excavation 20
Township were examined. There are many active and potential Water + Dissociation 22
landslide zones in this region. Morphology, geology, land Excavation + Dissociation 11
; s Los rat A of the Rm is eret Wales + Excavation + Dissociation 10
| e aim of this study is; producing a landslide risk map an : "ue ; 3 ;
| s M p gak ng F Water + Dissociation + Plant Cover Changing 9
| giving some precautions before the planning of the settlement. =
Others 5
2. CAUSES OF LANDSLIDES Table 1. Causes of Landslides
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For the landslides, water flow, excavation, dissociation of the 3. FORMS OF LANDSLIDES
rocks and changing of plant cover are the main reasons. The
along effects of these causes facilitate the landslide occur. Snaps
According to topographical conditions and excavations, sliding
movements turns to fall downs. Because of not doing stability
analysis for excavations for settlement and transportation
constructions, there are many landslide occurs in potential
landslide zones. Also, changing the plant cover for earning new
agricultural fields or growing up more beneficial crops
improves the landslide risk. In addition to them natural
As a result of snapping of soil and rocks, mass falls, leap, hop
or roll freely. There is a little or non effect between the units
during the snapping. Movement may change from fast to very
fast. There may be little movements before the main
movements. The main reasons for snaps are climate, frost, and
dissociation of the blocks by hydrostatic effects, dynamite
explosions and carvings of the waves.
* Corresponding author.
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