Abstract
The Mayoon landslide in the Hunza District is a slowly developed, non-catastrophic landslide that has gained its importance in the last few years after its rapid activation and fast slip rate. The area is characterized by high earthquake hazards (zone 3 with a peak ground acceleration value of 2.4–3.2 m/s2) by the Building Code of Pakistan due to frequent earth quakes. The past high earthquake activity in the area has displaced the foliated rocks towards the south and is responsible for opening the bedrock joints. The head and body of the landslide are covered by unconsolidated material and have fractures of varying lengths and widths. The non-invasive geophysical techniques, including Ground Penetrating Radar (GPR) and Electrical Resistivity Soundings (ERS), are deployed to evaluate the Mayoon landslide subsurface. The subsurface is interpreted into a two-layer model. Bright reflectors and highly variable resistivity characterize the top layer (Layer-1). This layer is associated with a loose, highly heterogeneous, fragmented material deposited under glacial settings over the existing bedrock. Hyperbolic reflections and intermediate resistivity characterize the bottom layer (Layer-2). This layer is associated with foliated metamorphic bedrock. The hyperbolic reflections show faults/fractures within the bedrock. The extension of these fractures/faults with depth is uncertain due to decay in the GPR signal with depth. The intermediate resistivity shows the bedrock is weathered and foliated. Reflections within Layer-1 have disrupted directly above the fractures/faults suggesting a possible movement. A bright reflection between the two layers highlights the presence of the debonded surface. Loose material within Layer-1 coupled with debonding possesses a significant hazard to generate a landslide under unfavourable conditions, such as an intense rainstorm or earthquake activity.
Highlights
North Pakistan territory gains its uniqueness in hosting younger mountain belts, glaciated peaks, rugged topography, deeply incised valleys, and multiple mountain hazards
This study provides near-surface characterization of the Mayoon landslide by incorporating the Ground Penetrating Radar (GPR) and Electrical Resistivity Soundings (ERS) geophysical techniques to address the site’s hazards
It is characterized by relatively weak amplitudes and by many hyperbolic reflections primarily seen between horizontal distances 240-260 m, 275-285 m, 320-340 m, 365-385 m, 408-415 m, and 3-6m below ground level (BGL)
Summary
North Pakistan territory gains its uniqueness in hosting younger mountain belts, glaciated peaks, rugged topography, deeply incised valleys, and multiple mountain hazards. Hunza-Nagar Valley in North Pakistan is located in the Karakoram Mountain range and is strongly affected by devastating landslides (Bacha et al, 2018). The National Disaster Management Authority (NDMA) of Pakistan has marked the area as highly vulnerable to flash floods, avalanches, and landslides. Landslides are a frequent mountain hazard that pose a great threat to the community and infrastructure. The understanding of the deformation mechanism of a landslide improves our knowledge of its episodic evolution. This evolution depends on various factors, such as hydrology, tectonics, Rehman, Q.; Ahmed, W.; Muhammad, W.; Khan, S.; Farid, A.; Shah, SHA
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