The Mazar Hydroelectric Plant is located in the Andes Cordillera in south-central Equator. The study area corresponds to the middle source of the Paute River Basin which is nestle in a narrow valley at about 2,000 metre above sea level. Many landslides are observed along the Paute River, including the historic case "La Josefina" which in 1993 moved a volume of soil and rock estimated at 25 million m³. For the construction of a large engineering project in this geological context characterized by many natural instabilities is essential to identify the spatial distribution of the landslide hazard. Furthermore, in order to obtain satisfactory results in timely with reduced costs, the use of back-calculation meth-ods and techniques of geoprocessing are facilitators’ tools. In this aspect, this paper presents the strength parameters of colluvium soils and rock horizon that form more superficially the slopes bor-dering the hydroelectric reservoir were determined by back-calculation and, to attest the reliability of the results, were compared with literature values. The factor of safety (FS) was calculated as a function of the degree of ground saturation and the groundwater level in regions above the reservoir, therefore, not submerged. The FS was also evaluated the seismic contribution applying acceleration coefficient Kh of 0.14 g and another overestimated (Kh = 0.28 g). The spatial distribution of the FS, through geo-processing, resulted in maps of guidance character about the areas of lesser and greater stability for each simulated situation.
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