Application of Fuzzy Algorithm for Assessing Seismically Induced Landslide Hazard for an Important Road Corridor in the Lower Indian Himalayas

Abstract

A critical part of planning and managing road infrastructures in mountainous regions is thepragmatic assessment of the prevailing and credible landslides hazard. Such assessments assumegreater significance for the Himalayan region, where seismically induced landslides present agreater threat than commonly recognized, and require a robust comprehension of two hazards:earthquake and the landslides induced by the former. However, the traditional practice oflandslide hazard assessment often neglects seismic factor due to paucity of pertinent data, whichmay further be ascribed to the rarity of an extreme event. In this context, an endeavor has beenmade in this study to evaluate the seismically induced landslide hazard for a scenario earthquakeof 10% exceedance probability in 50 years for an important road corridor in the lower IndianHimalayas using Fuzzy algorithms. Probabilistic Seismic Hazard Assessment (PSHA) has beencarried out for the study area to calculate the Peak Ground Acceleration (PGA) of the scenarioearthquake, which is then used as a landslide triggering factor. PGA is integrated with eightdifferent landslide controlling factors viz. lithology, slope angle, aspect, elevation profile,distance form fault, distance from drainage, distance from road, and land-use-land-cover patternsin a Geographical Information System (GIS). 232 numbers of landslides are mapped for thestudy area using high resolution Google earth imagery platform. The Fuzzy Cosine Amplitudemethod is used to define the degree of similarity (strength of correlation) between the observedlandslides (dependent variable) and the landslide causative factors (independent variable(s)).Expectedly, the probability of landslide occurrence correlates (degree of similarity) to the PGAin a linear pattern (goodness of fit = 0.9954). The result of the study is discussed in terms of aseismically induced Landslide Hazard Zonation (LHZ) map for the study, which is generatedusing three Fuzzy operators (AND, OR and GAMMA). The prepared LHZ map demarcates morethan 40% of the study area as the zones of high to very high landslide hazard under the scenarioearthquake, with a prediction accuracy of 80%. The study shows that probabilistically generatedPGA can be included as seismic parameter for a more comprehensive assessment of the landslidehazard in seismically active regions.Keywords: Fuzzy Cosine Amplitude, Probabilistic Seismic Hazard Assessment (PSHA), PeakGround Acceleration (PGA), Landslide Hazard Zonation (LHZ), the Himalayas