Himalayan Geology, Vol. 41 (2), 2020, pp. 222-233, Printed in India
Review of the current practice on inclusion of seismicity in landslide susceptibility zonation: A case study for Garhwal Himalaya
RITU RAJ NATH*, MUKAT LAL SHARMA, ARUN TYAGI
Department of Earthquake Engineering, Indian Institute of Technology-Roorkee, Roorkee, 247667, India
*Email (Corresponding author): riturajnath14@gmail.com
Abstract: Landslide Susceptibility Zonation (LSZ) of an area becomes very important in the mountainous regions where by the area is divided into near-homogeneous domains, and ranked as per their degree of susceptibilities to potential hazard due to mass movements. This LSZ maps are helpful in recognizing the risk associated with landslide hazard, and should be used for rational land-use practice to reduce the impact of a catastrophic disaster. The current practice of LSZ mapping is based on the identification and analysis of various landslide causative factors with respect to the prevailing environment of a specified area. Two sets of causative parameters are widely accepted: the internal/preparatory and the external/ triggering factors. In general, the presently available methods for LSZ practice can be broadly divided into two major categories: the qualitative approach and the quantitative approach. The qualitative approach is based on assessment of various landslide causative factors of an area and then assigning the appropriate rank and weight to each causative factor, which are then numerically integrated to produce the LSZ map. This approach although being very easy and fast, transpires to be subjective and needs experience and professional judgement to be applied accurately. In quantitative approach, the relative importance of various causative factors is ascertained in objective ways to minimize the subjectivity of weight assignment process. Here, the quality of the input dataset controls the final outcome. An attempt has been made in this study to review and comprehend the various available methods for preparing LSZ maps for mountainous terrains. Special attention has been paid to the Garhwal Himalayan belt which exhibit both high percentage of slope failure as well as hyper active seismicity. Critical examination of the available literature reveals that non-inclusion of seismicity in LSZ maps for seismically active mountainous belts may lead to erroneous practicing. Although, correlation between seismicity and landslides has been established, seldom the tectonic set up beneath the major landslides is considered as an internal causative factor in preparation of LSZ maps for this area. It has been observed that there exists multiple methods for LSZ mapping and the selection of a particular method is governed by the scope and scale of the investigation, along with the quality of the dataset available. The study suggests that incorporation of strong ground motion scenarios generated through Probabilistic Seismic Hazard Analysis would augment the current practice of LSZ mapping for seismically active regions like the Garhwal Himalaya for more realistic results.
Keywords: Landslides, Susceptibility, LSZ mapping, Seismicity, Garhwal Himalaya.
