Pattern Recognition to Identify Susceptible Areas in Northwestern Himalaya

Regions in northern India, especially within the Himalayan arc, have experienced frequent disastrous earthquakes. Major seismic activity in India is concentrated along the geologically young and seismo-tectonically active Himalayan arc. An area between the latitude 25° N to 35° N and longitude 72° E to 90° E was considered for the study, which falls between the great Kangra earthquake of 1905 and the great Bihar–Nepal earthquake of 1934. The main objective of the study is to identify the areas of high seismic susceptibility using pattern recognition (PR) exercise. Areas which have experienced high seismicity and have complex tectonics are more prone to much frequent seismic activity in future and are defined as seismically susceptible areas. The pattern recognition technique started with the identification, selection, and extraction of features from the seismicity and tectonic data. Various features were identified from a circle of radius 25 km around each epicenter, known as the central earthquake. These features were then subjected to discriminant analysis, which constituted the training exercise of the PR technique. The discriminant functions obtained from this training exercise were then applied for the decision-making exercise to identify the susceptible areas. This resulted in the identification of susceptible area within the study area in the form of clusters. Various clusters were identified along the Himalayan arc, which are capable of producing damaging earthquake of significant magnitude. A dense cluster was observed between the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT), and Kishtwar Fault in west and Sundernagar Fault in east. The great Kangra earthquake is part of this dense cluster. A great amount of seismicity was also observed around MCT, east of Sundernagar Fault, in Uttarakhand and western Nepal. Epicenters of Uttarkashi (M_w = 6.8) and Chamoli (M_w = 6.7) earthquakes are within this cluster. Other dense clusters were also observed which trends transverse to the Himalayan arc and follows the Kaurik Fault system and in the vicinity of Lake Lighten Fault, in the Kashmir Tibet region.