Hazards Probability In Zagros Fold Belt (ZFB), SouthWest Iran: Aided by Remotely Sensing & GISSaied Pirasteh Faculty of Engineering , Islamic Azad University Dezful Branch , Dezful (Iran) moshaver1380@yahoo.co.uk Amir Mahmoodzadeh Faculty of Engineering Islamic Azad University Najafabad Branch Najafabad (Iran) SMA Rizvi Department of Geology Aligarh Muslim University Aligarh (India) Abstract The present study area belongs to the Zagros Fold Belt (ZFB) southwestern Iran and is parts of Alpine Himalayan orogen that suppose to be newly active zone. Information generated through remotely sensed data and GIS techniques. Digital elevation model (DEM), stability and saturation zones, drainage basin network, geological map were extracted and analyzed in conjunction with several field visits to deduce the landslide, rockfalls zones. Buffering techniques were applied to estimate probability of hazard on infrastructure caused by landslide and rockfalls. Buffering techniques indicate that there will no be any loose of infrastructure in the study area while railway line passes this area. The study reveals the influence of rock type for the development of the drainage patterns. This study indicates that the development of the landslides and rockfalls in the study area is not affected by moisture but it is influenced by topography, development of lineaments and chemical reaction phenomena. This study also reveals that the applications of remote sensing and GIS for the engineering geology in the ZFB while the railway transportation line of Tehran-Andimashk passes the area with many tunnels and bridges. 1. Introduction The satellite image data beside GIS techniques become essential tools for study of the most natural hazards in all of the world. Remote sensing methods and GIS techniques have been proved to be a very useful tool in monitoring and mapping zonation of the landslides and rockfalls. The natural hazards such as landslides and rockfall have been studied for the Mazou area in the Zagros Structural Belt. The Zagros Structural Belt is a parts of the Himalyan orogen and suppose to be a newly active zone (Berberian, 1977) and (Pirasteh et al, 2002). Faults, folds and lineamants are the most common elements of structural features. Conventional geological mapping of structures like faults, folds and lineaments for structural analysis have provided useful information on structure and stress distribution in small area (Bucher,1920, Friedman, 1972, McQuillan, 1973, Davis, 1984). The Landsat-7 ETM (Enhanced Thematic Mapper)-2002, False Color Composit (FCC) 4-3-2 bands which is covering part of south-west of Iran (Figure.1) has been digitally processed to enhance the visibility of landslide and rockfall zones. The image interpretational elements such as tone, erosion, landform, topography and drainage system were used in order to distinguish the landslide and rockfall zones from space and then several field checks have been carried out in conjunction with GIS techniques. The Global Positioning System(GPS) is used to determine the geographical location of the landslides and rockfalls in the field surveying. The DEM of the study area was produced to extract the stability zones (Figure 4), saturated zones (Figure 5), drainage network system as various GIS coverages (Figure.4) and their relationships/topology to landslides and rockfalls in the area. The study can be proposed a model for landslide and rockfall zonation and hazard estimation for 100 meters extent within a GIS environment. The present area was divided in X, Y and Z zones (Figure.1) according to the rock types and topography to correlate the different landslide and rockfall zonation(Table.1). This study has been selected due to its importance from natural hazard prospective while railway transportation line of Tehran- Andimeshk crosses the Mazou region. 2. Study Area The study area is situated in the Zagros Structural Belt (ZSB) in the south west of Iran (Figure.1) covering Latitude 32° - 45'- 4.29'' - 32° - 52' – 29.46'' N and Longitude 48°- 29'- 16.50''- 48°- 37'- 49.35'' E and with respect to universal transverse mercator (UTM) coordinates is 264964.500mE-3640020mN, which is located north of the Dez dam (Dezful city) and northeast of Andimeshk city in the Khuzestan province in southwest Iran. The satellite data scene is with path and row 166/038. The area can be reached by the Andimeshk-Tehran railway line. The temperature in the area normally ranges between 0 to 45 degrees centigrade.  Figure1. Study area 3. Geological Setting Geologically speaking the Zagros Structural Belt consists of different lithological units ranging in age from Cretaceous to Subrecent and Recent. The geological prospective of the study area indicates lithology in age from Oligocene-Recent (Figure 2). The present study area mostly comprises dolomite, limestone, sandstone, silt, red and grey marls, gypsum and anhydrite and Recent alluvial. Net erosion rates are varied within 10m/MY – about 162.5m/MY (Ali et al, 2003). Generally sediment flux is a critical variable in controlling erosion rates. Faults, folds and lineamants are the most common elements of structural features.  Figure 2. Digital Geological Map of the study area, ZSB, SW-Iran 4. Materials We used predominantely the following items: 4.1. Softwares ENVI 3.6 (Environmental Visualization Image), Arcview 3.2, Microstation J, Arcinfo, ER-mapper 6.1, RiverTools 2.4 4.2. Other materials Geological map 1:100000, Landsat-7 ETM data of 2002, path/row 166/038, landuse map of scale 1:25000 and digital topographic map 1:25000. 5. Methodology The flowchart of the methodology has been given in Figure 6. The below steps have been processed for the creation of the landslide and rockfall zonation in the Mazou region of the ZSB, southwest Iran. 5.1. Geometric correction Theoretically, geometric correction is undertaken to avoid geometric distortion from a distorted image, and achieved by establishing the relationship between the image coordinate system and the geographic coordinate system using calibration data of the sensor, measured data of position and attitude, Ground Control Point (GCP) (using GPS). Geometric correction process has been done represents for all sides of the Landsat ETM image dated 2002, and not enough GCP points could give a bad result. UTM information from landuse and topographic 1:25000 scale, maps used for references on geometric correction process. This above process was done in ER-Mapper software 6.1 versions. 5.2. Enhancement Basically enhancement process is applied to enhance objects in the image. Linear 2% enhancement was applied to the image using ENVI software to extract the landslide and rockfall points with the help of image technique elements. Filtering process was also used to make sharpen the objects on the images to varify the lithology, faults and folds. This process was done with the help of ENVI software. 5.3. Creation of DEM The digital topography maps in digital graphic numbers (DGN) format from Iranian Surveying organization (ISO) have been converted to text (txt) formats with the help of Microstation J software and finally were introduced to Arcview software to interpolate grid, create TIN model (Figure. 7) and produced DEM. 5.4.Delineation of drainage networks Simultaneously, the text formats were introduced to other GIS softwares called Rivertools 2.4 to create DEM for analyzing the drainage network (Figure 7) and to address analysts for the identification of unstable zones, rock types, slopes and geology of the study area. Extraction of drainage network involves three conditioning processes. They are: *Flow grid generation- the objective of the first step in the conditioning phase is to create an adjusted “depression-less” are raise to the lowest elevation value on the rim of the depression. Each cell in the depression-less digital elevation data set will then be part of cells leading to an age of the data set. A path is composed of cells that are adjacent horizontally, vertically, or diagonally in the raster ( eight-way connectedness) and that steady decrease in value. The purpose of this routine is to extract a flow grid from a DEM grid. ** Basin outlet- This is a graphic routine that allows one of specify the basin that one wants to analyze by providing Rivertools with the precise location of the basin’s outlet. In the present study the complete DEM was used and therefore an outlet was specified in the GIS environment on DEM on the basis of the remotely sensed data and filed checks. ***RT Treefile- This routine creates a Rivertools “treefile” for one or more of the basins in the DEM, from a Rivertools flow grid. The treefile is a vector format file, which can store data for many disjoint basins. Every pixel in the particular basin is the outlet pixel for a sub-basin that is contained in that basin. Detailed morphometric analysis of the drainage network (Table.1) was done for the watershed to deduce and interpret its influences on the landslides and rockfalls.  The Landsat-7 ETM-2002, FCC of bands 4-3-2 was used in ENVI software to extract the lithology of the area. The geological map of scale 1 :100000 of Oil Company Of Iran was calibrated to the satellite data across field visits. Digitization process was applied on Landsat data to discriminate the lithology of the area. To create a geological map with attributes within the GIS, the vectors were converted to the Arcinfo format to produce topology. Then data was converted to Arcview softeware format to deduce geological map of the study area. 5.6. Extraction of the Stability and Saturation Zones DEM is used to obtain the necessary input information (slope and specific catchment area). Parameters are allowed to be uncertain following uniform distributions between specified limits. These may be adjusted (and calibrated) for geographic calibration regions based upon soil, vegetation or geologic data. The methodology includes an intractive visual calibration that adjusts parameters while referring to obsereved landslides and rockfalls. Stability Index Mapping (Sinmap) extention utility of the Arcview software from the GIS softwares was calibrated by introducing the required parameters such as soil cohesion factor, phi factor and rma06003_4s parameter (R/T)to prepare stability (Figure.3) and saturation zone (Figure.4).  Figure 3. Showing stability zone map of the study area in ZSB, SW Iran  Figure 4. Showing saturation zone map of the study area in ZSB, SW Iran 5.7. Extraction of Landslide and Rockfall points The landslide and rockfall point zonations were extracted from the Landsat ETM-2002 using image interpretation elements then calibrated to the stability map (Figure.3). To take up the accuracy for the interpretation in the image, GPS was used in the several field checks (Figure.5). The location of the landslides was noted and converted to the GIS formats and then introduced to the Arcview software. Sinmap extention utility of the Arcview software was calibrated by introducing the required point theme.  Figure 5. Showing the probablity of the rockfalls (unstable area) influence by topography, rocktype, erosion and mositure. Location: in Y-section of the study area. 5.8. Buffering Buffer zones are used to define spatial proximity (Figure.7). For the landslide and rockfalls, a buffer zone was created to prescribed extent around point. Feature of a theme as rockfall was selected within an Arcview softeware. The distance selected as meter and then dissolve barrier between buffer was applied. This type of the buffering used to estiamte the probablity loose damage area caused by rockfall or landslide.  Figure 6. Flowchart of the method used 6. Results & Discussions The use of satellite imagery facilitated easy mapping and focus on a large area for our interpretations. DEM of the study area is mainly used due to the inaccessibility with the rugged topography. So the satellite digital data across the DEM prohibits frequent and easy analysis rather than hard field visits. The GIS coverages model for the landslide and rockfall hazard in the study area belong to the different zones can be seen on Figure. 7. The study area was described as follows: *Section X: The landslide and rockfall hazard could be illustrated in the X-zone of the study area. From engineering geology prospective north parts (i.e.zone-X) of the study area where the topography varies between 600-1700 meters, covered by Asmari formation (Table.1) exhibits maximum natural hazards ( rockfall and landslides). That is because of the high topography, lithology of the area and maximum tectonic activities and deformation with presence of faults and lineaments (Ali and Pirasteh, 2004) therefore results the unstable zones than Y and Z zones. Ground data indicated that reaction of water with the present lithology like gypsum and limestone caused material to be loosed and generate landslide and rockfalls in the north part of the study area. So the combined data shows that parameters such as topography, lithology, chemical reaction of materials with water, drainage system, erosion (Ali et al, 2003) and tectonic activities are related to the landslide and rockfalls (Table.2) and each does act an important role in generation of the landslide and rockfalls in the study area. It has been seen that the landslide and rockfall zones are mainly developed in a coarse drainage system network regions where the Asmari formation exhibited and is permeable.  **Section Y: The area is comprises red marls, limestone of Gachsaran formation. Drainages are subdendritic with medium to fine texture. This area comprises lower topography than section-X. This section is more stable with lower saturation than section-X. The density of the lineaments in this section is moderate to low (Ali et al, 2003). Presence of marls in this section becomes a cause to reduce the chemical reaction with water than sextion-X, where anhydrite and calcareous rocks are present. The lower topography, lower chemical reaction, presence of rock type, moderate to low density of lineaments and lower moisture make important roles for the stability of this section. ***Section Z: The area showing lower relief topography (350meter-550meter) than two above sections. This section comprises dendritic drainage pattern and medium to fine drainage in texture. Z-section is completely stable zone and no rockfalls and landslides are found. This is because of low topography, low density of the lineaments, low erosion (Ali et al, 2003) and presence of sandstone of Aghajari formation. However, It has been seen that to estimate the extent around the landslide and rock fall points in the study area while knowing that the railway line crosses, the techniques of buffering was good method for landslide and rockfall points. Buffering with 100 meters extent indicated that the railway line and other infrastructures can not be suffered by landslides and rockfalls. 7. Conclusion It has been seen that the landslide and rockfall zones are not influenced by moisture in the area but it is due to topography, reaction phenomena, more deformation in the X-section that two sections in the area and coarse drainage system. The study shows that also the drainage patterns in the study area are influenced by rock type. The present study also reveals a model for the landslide and rockfall hazard zonation (Figure.7). Finally, the buffering techniques have given good results to estimate the probability of the landslide and rockfall hazards. This paper also present the capability of the remotely sensed data and GIS techniques in different aspects of the earth science studies  Figure 7. GIS coverages for the landslide and rockfalls zonation and buffering to estimate probability hazard in the Mazou area, ZSB, SW-Iran Acknowledgement The author is thankful to authorities of Shahid Chamran University, Ahwaz-Iran. The work could not be done without cooperation of Mrs. Leila FarzinPur, so I also am thankful to her. References
|