SKS and SKKS Splitting Measurements Beneath the NW Himalaya

An experiment on SKS and SKKS splitting is carried out using teleseismic earthquakes recorded at 10 broadband seismic stations deployed in parts of the NW Himalaya. A total of 47 reliable splitting parameters is estimated using rotation correlation and transverse component minimization methods. A large variation of delay time ( δt ) of 0.3 to 1.6 s and polarization direction ( ϕ ) of 42° and 98° of the fast wave is obtained. A strong component of fast axes along the strike of the Delhi–Hardwar Ridge (DHR) near the Himalayan foothills is found to be correlated with the structurally controlled strain-induced shearing. The structural fabrics were likely frozen because of induction of past plate tectonics. The orientations of the fast axes surrounding the Main Central Thrust (MCT) are correlated with the foliation and folding caused by strike-orthogonal compression as well as underthrusting of the Indian plate beneath the Himalaya. A low value of 0.3 s delay time is proposed to be caused by multi-layered anisotropy. A two-layered anisotropy model developed for the stations Adibadri, Gaurikund and Chakrata reveals that the directions of fast axes in the shallow and deeper levels are parallel to the strike of the DHR and to the absolute plate motion (APM) vector of the Indian plate, respectively. We thus propose that the anisotropy observed in the NW Himalaya is a combined effect of the fossil anisotropy preserved in the DHR, the mantle flow and the foliation plane arisen due to collision between the Indian and the Eurasian plates.