Seismotectonics and crustal stress field in the Kumaon–Garhwal Himalaya

Abstract

We present fault plane solutions of 94 well located small-to-moderate sized (1.5 ≤ ML ≤ 5.4) earthquakes, which occurred in the Kumaon–Garhwal Himalaya during 2005–2008, using P-wave polarity and body wave amplitudes. These earthquakes show a mixture of thrust, normal and strike-slip type mechanism, with a majority of thrust type. Most of the thrust earthquakes occur at a depth of 8–22 km in the Main Central Thrust (MCT) zone and the Lower Himalaya. The spatial distribution of these earthquakes suggest that the strain resulting from the ongoing collision of the Indian plate with the Eurasian plate is being consumed by thrust fault movement mainly on the north dipping Munsiari Thrust and south dipping Tons Thrust. The strike-slip earthquakes are mainly observed in the Lower Himalaya as well as around the Munsiari region in the MCT zone. The normal earthquakes are also observed in different parts of the Kumaon–Garhwal Himalaya and the Gangetic plain. Their occurrence is attributed to the local structure(s) as well as the flexure of the Indian plate. Stress tensor inversion of the calculated fault plane solutions indicates that the maximum compressive stress in the Gangetic plain is N–S directed and near vertical; whereas in the Kumaon–Garhwal Himalaya, it is near horizontal and NNE–SSW directed, and correlating with the prevailing stress condition due to northward movement of Indian plate