Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India |
| |
Authors: | Shashi Prakash Sharma K Anbarasu Saibal Gupta and A Sengupta |
| |
Institution: | (1) Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, West Bengal, 721302, India;(2) Department of Civil Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721302, India |
| |
Abstract: | Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to
heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required
to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of
the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide
are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust
passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important
to identify the subsurface structures that channel water below the landslide surface in order to understand the triggers of
slide activity. This can only be accomplished by geophysical survey; however, an appropriate geophysical technique that can
be applied in such terrains must be identified. Very low-frequency (VLF) electromagnetic survey was performed over the Lanta
Khola landside in order to delineate subsurface structures. Although a very limited number of VLF transmitters are available
worldwide, it was possible to pick up VLF signals from a number of VLF stations even in this high-altitude mountainous terrain.
VLF measurements along five profiles perpendicular to the geological strike were recorded, and a high conducting zone was
delineated from the VLF observations. This conducting zone correlates with the low resistive zone identified from gradient
resistivity profiling. The anomalies confirm that there is a water-saturated zone (soggy zone) even in the subsurface of the
slide parallel to the geological gneiss–schist contact within the Lanta Khola slide. This indicates that the conductive feature
correlates with a weak water-saturated debris layer that lies along the slide and is parallel to the geological contact. Resistive
structures on either side of the landslide zone can thus be correlated with the stable ground. It is necessary to drain out
water from the soggy zone to minimize slide activity since this zone appears to penetrate into the body of the slide. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|