METHODS OF ANALYSIS

GIS is the main technique utilized in this study. It is used to identify and map the distribution of landslide hazards in the region, and the risky areas for settlement. GIS is used to prepare a base map of the study area and to show the high landslide risk areas by creating a 3D image, overlapping the base map with buildings, roads, references points and elevation contours. A digital map of the region is used to prepare various thematic maps, like slope, geology, elevation, buildings, and roads. An aerial photograph of the region is used to prepare a 3D zonation map. GPS (Geographic Position Systems) field data provide recods of actual landslides and damaged buildings, or area around buildings under landslide risk, help show the hazards.

The research area was selected by studying the available data and needs of the community. A 3D GIS map was produced to show the distribution of data in the research area (Figure:8-9).

Figure-8:3D GIS elevation map of study area

Figure-9: GIS contours map of study area

One widely used method is to define slope in the field by mapping the breaks of slope delimiting facets and the changes of slope between the elements (H. Bryant, 1997). From elevation map is produced slope and aspect maps of research area (Figure- 10-11).

Figure-10: Slope map of study area

Figure-11: Aspect map of study area

From analyses of field observations, and eyewitness accounts, the principal causative factors of the landslide are interpreted as geological, hydrological and anthropogenic (S.N., G.T., P., 1999). All these data are foundamental data both for the mapping of the hazard zones and for the modeling of the mechanism of slope failure (G. and A., 1999).

Aerial photographs from 1996 were compared to ground surveys to identify landslide areas. A mapped distribution of the landslides are concentrated between 84m and 154 m on research area (Figure-12). “ Also, I produced table by statistical measurements taken from the field study . Morever, the yellow points on the map and table shows concentrated landslides on the research area “(Figure-13).

Figure-12: Concentrated landslides on the study area

Figure-13: Statistical measurements by field trip on study area

Beside of this, the letters (yellow points) on Figure-12 show evidence of landslides by taken objective photos on the field trip (Photos at below).

Photo-A: An example of mudflow type of landslide

Photo-B: Sliding example near E-5 Highway

Photo-C: Sliding and mudflow example in front of the site

Photo-D: Mudflow and sliding on the slope and behind of buildings

Photo-E: Sliding and mudflow with clay soil formation in front of buildings across to good sea view

Photo-F: Sliding with vegetation cover near E-5 Highway

Photo-G: Sliding example with buildings under danger

Photo-H: Landslide damage on the wall shape

Photo-I: One building under danger on sliding

Moreover, there is done danger area and potential danger area maps of landslide area by using field trip observation data to be reference in present and near future for engineers and constructers on new settlements ( Figure-15-16 ).

Figure-15: Landslide danger area in study area, Büyükçekmece

Figure-16: Landslide potential danger area in study area, Büyükçekmece