Landslide susceptibility zonation mapping using statistical index and landslide susceptibility analysis methods: A case study from Gindeberet district, Oromia Regional State, Central Ethiopia

The present study was carried out in Gindeberet district, central Ethiopia and covers a total of 128 km(2). The geology of the area is comprised of sandstone, mudstone, limestone and basalt. The general objective was to evaluate the factors influencing the landslide initiation and to prepare a landslide susceptibility zonation map. One hundred thirty landslides were identified through field investigation and Google Earth image interpretation. Statistical Index Model (SIM) and Landslide Susceptibility Analysis (LSA) were used for the preparation of landslide susceptibility map. Lithology, slope steepness, aspect, land use/land cover, and distance from drainage are the causative factors selected, whereas rainfall and human activities are considered as the triggering factors. The relations of landslides and causative factors were determined in terms of weighted value (W-ij). From the lithology limestone, mudstone and weathered basalt have strong relationship with the landslides. Moreover, the result shows that weighted values (W-ij) are high for N and W orientation class of slope aspect; greater than 45. slope steepness; agricultural land and moderately vegetated land use/land cover class and 0 100 m and 100 200 m distance from drainage class. Landslide susceptibility zonation (LSZ) map was prepared and classified into very low, low, high, and very high susceptible zones. For LSZ map prepared by SIM model out of 130 landslides inventory data, 2 (1.54%) of the landslides fall in very low susceptible zone, 11 (8.46%) in low susceptible zone, 12 (9.23%) in moderate susceptible zone, 16 (12.31%) falls in high susceptible zone and 89 (68.46%) in very high susceptible zone, whereas LSZ map prepared by LSA model shows that out of 130 landslides inventory data, 11 (8.5%) of the landslides fall in very low susceptible zone, 12 (9.2%) in low susceptible zone, 15 (11.5%) in moderate susceptible zone, 25 (19.3%) in high susceptible zone and 67 (51.5%) in very high susceptible zone. The percent of existing landslide determined from LSZ maps prepared by SIM and LSA falls in high and very high susceptible zones were 81% and 71% respectively. The result of verification shows that areal distributions and occurrences of landslides were relatively comparable in both methods.