Landslides in Rock Slopes During January 19, 1975, Kinnaur Earthquake in Himachal Pradesh, India

Ground failures in rugged terrain with more than 10,000 ft (3000m) elevation above mean sea level in the epicentral tract of 19 January 1975 Kinnaur earthquake in Himachal Pradesh, India, indicate that most of the earthquake generated landslides occur in surficial cover. The collapse of such material on steep slopes often result in cascading rock avalanches obliterating roads and other constructions lying on its way. The accumulated debris during this earthquake dammed Parachu river creating a reservoir behind it. The dislodging, overturning and uplift of boulders on hill tops and scabing and slabing of rocks along joints and other weak zones resulting in loosening, dilation and crumbling of frozen formations indicate that seismic waves incident on rock slope surface and near ground discontinuity surfaces filled with frozen ice on reflection as tensile stress waves shattered the ground. The study indicates the significance and desirability of detailed study of surficial cover on rock slopes in mountainous terrains for evaluation of stability of hill sides during earthquakes. In high altitude frozen ground and rock slopes, seismic stress waves play a significant role in shattering near surface rock mass.