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Most of Sikkim vulnerable to earthquake-induced landslides

Hilly regions, especially ones which receive heavy rainfall and are located in earthquake-prone regions, are likely to suffer frequent landslides. Landslides occur when masses of earth or rock collapse from a mountain or cliff. They can pose a big threat to life and property.

The Indian state of Sikkim is no exception. Situated in the Himalayan belt, the region faces frequent landslides. The recent earthquake in adjoining Nepal triggered many landslides in Sikkim. This motivated a recent study by Naveen James and Prof. T G Sitharam from Department of Civil Engineering, IISc, to assess the vulnerability of Sikkim to landslides, especially those induced by earthquakes.

James explains, “Landslide is a major natural disaster that affects most of the hilly regions all over the world. Major causes for a landslide are intense or prolonged rainfall and earthquakes.”

Sikkim is situated close to the Himalayan belt, one of the most earthquake-prone areas in the world, and as a result is highly susceptible to earthquake induced landslides. The aim of the study was to assess the scenarios that could lead to landslides in Sikkim.

Explaining the scientific relevance of this study, James says, “The previous research works in the area of landslide hazard assessment have come up with many qualitative landslide hazard maps. However, in this study, the seismic landslide hazard for the Sikkim state (macro-level) is assessed in a quantitative manner, which is one of its kind.”

To estimate the seismic hazard at the state level, the mapping technology Geographic Information Systems (GIS) was used. The researchers identified and characterised earthquake sources in the study area. They then divided the state into grids, and calculated the maximum possible magnitude of the earthquake sources, and the minimum distance between the earthquake source and the points on the grid. Combining this information with the slope of the area, the team were able to calculate the earthquake intensity the area could resist, without forming landslides. These values depended on the type of soil and its slope.

Based on the analysis, the researchers could classify the grids in Sikkim into three classes – high, moderate and low risk of landslides. Most of Sikkim falls under the high hazard zone. “It now becomes feasible for engineers to estimate the 'vulnerability' of a particular location. This defines how well or how poorly human lives and infrastructures are protected against the landslide hazard”, says James.

“The highlight of this study is that it was carried out at very finer resolution of 30m × 30m grid size”, added James.

The study can help identify vulnerable zones in order to plan mitigation efforts and provide a good database for decision-making while planning big projects.

About the paper: “Macro-Level Assessment of Seismically Induced Landslide Hazard for the State of Sikkim, India Based On GIS Technique” appeared in IOP Conference Series on Earth and Environmental Science.

About the authors: Dr. Naveen James is an Assistant Professor in Department of Civil Engineering of BITS Pilani (Hyderabad campus), and Dr. T. G. Sitharam is a Professor in Department of Civil Engineering of Indian Institute of Science, Bangalore.