Spatial analysis of mutual fault, fracture and slope controls on rocksliding in Darjeeling Himalaya, India

In this paper, the Fry analysis was applied to study the spatial patterns (in terms of trends) of rockslides; proportion analysis was applied to study the spatial associations between rockslides and slope aspects; and distance distribution analysis was applied to study the spatial associations of rockslides with different sets of faults/fractures based on trends. In a study area in the Darjeeling district (India), the results of applications of these spatial analytical techniques support a proposition of mutual fault/fracture and slope controls on rocksliding. In different parts of the study area, deep-seated rockslides are associated with (a) NE-trending faults/fractures and SSE-facing slopes, (b) NW-trending faults/fractures and ENE-facing slopes, and (c) NNE-trending faults/fractures and SE- or ENE-facing slopes; whereas shallow translational rockslides are associated with (a) NNE-trending faults/fractures and SE-, NW-, WNW- or WSW-facing slopes, (b) WNW-trending faults/fractures and SW-facing slopes, (c) NNW-trending faults/fractures and ESE- or SW-facing slopes, and (d) NW-trending faults/fractures with SW-facing slopes. Creating and integrating spatial evidence layers representing mutual fault/fracture and slope controls on rocksliding can be achieved satisfactorily via application of evidential belief functions. A predictive map of rockslide susceptibility derived by using slope aspects, slope inclinations and proximity to the faults/fractures that are spatially associated with rockslides is superior to that derives by using slope aspects, slope inclinations and proximity to all faults/fractures. The proposed analytical methods are suitable for first-pass regional-scale assessment of rockslide susceptibility.