A preliminary one-dimensional crustal velocity model for Himachal Pradesh, India

A preliminary one-dimensional (1D) velocity model for Himachal Pradesh, India has been developed by utilising the P and S wave travel time data. A very steady and narrow velocity model was obtained with travel time inversion, and a range of velocity models were tested with earthquake locations to derive the best-fit velocity model. The 1D velocity model proposed for the study region has seven uniform layers with interfaces at depths of 0, 5, 10, 15, 20, 25 and 30 km with P wave velocity of 5.219, 5.314, 5.391, 5.392, 5.964, 6.071 and 6.073 km/s and S wave velocity of 2.998, 3.015, 3.134, 3.135, 3.441, 3.482 and 3.647 km/s, respectively. According to the proposed model, the Moho in this part of the Himalaya lies at 60 km depth on an average. For P and S waves, the station correction ranges from −0.88 to 1.50 and −0.58 to 3.59 s, respectively. This low variation in station residuals indicates small lateral velocity changes that confirm the accuracy and stability of the proposed 1D velocity model. Using the new derived 1D velocity model, the earthquake epicentres were relocated and we observe a shallow seismic activity in the region at <30 km depth that clearly describes the ongoing convergence of the India-Eurasia plates in the study region. This study also infers a new, highly active seismic window in the latitude range of 31.8 °N to 32.8 °N and longitude range of 76.8 °E to 78.8 °E in the study region across the Kaurik-Chango fault, a causative fault for the 1975 Kinnaur earthquake.