The 2012 Ahar-Varzegan earthquake and its aftershocks have not only caused huge damage with a severe loss of life and property but also induced many geo-hazards with the major type of collapse, creep, slip, debris flow, and fallings that are generally considered as landslide in this study which can cause continuous threats to the affected region. in this study, a semi-automated geo-hazard detection method has been presented to determine the Landslides due to 2012 Ahar-Varzaghan earthquake in area from Ahar to Varzaghan by the use of bi- temporal Landsat images from before and after the earthquake. The accuracy of the results was checked out using field observations, Google Earth images and the error matrix. The results of the visual validation with the Google Earth images showed that the used method can detect landslids with relatively high accuracy.The images of landsat5 and 8 Because of their multispectral advantages can be used as a suitable data source for research on Instabilities. Finally, the validating results obtained by using the error matrix showed the total accuracy of 92.1% and kappa coefficient was 0.99. So based on the results obtained from the above method, the landslides were distributed mainly in slopes between 15 and 40 degrees and the height distribution of instabilities of 1420 to 2000 meters. Also based on vegetation indices, density of landslides have been increased after the earthquake. Generally unstabel slopes are located along river valleys and roads in mountain regions with deep valleys and steep slopes. According to the nature of present study, the obtained result can be useful for environmental planners and project developers.