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

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

Keywords: Fuzzy Cosine Amplitude, Probabilistic Seismic Hazard Assessment (PSHA), Peak
Ground Acceleration (PGA), Landslide Hazard Zonation (LHZ), the Himalayas