Lithosphere structure in the collision zone of the NW Himalayas revealed by alocal earthquake tomography

In this study, we obtained new 3D seismic tomography models of the crust and uppermost mantle beneath the northwestern Himalayas down to a depth of 120 km. The data were provided by the India Meteorological Department (IMD) and complemented by the Global International Seismological Centre (ISC) Catalogue. The distribution of anomalies correlates with the main geological features of the region. Specifically, the mountain ranges of the Greater and Lesser Himalaya stand out as a low-velocity anomaly, and the Indian Plate is visible as a high-velocity anomaly underthrusting the Himalayas. The Indian Plate not only underthrusts northwards below the Himalayas, but also bends westwards as it gets closer to the Hindukush Region. A peculiar feature of the model is a high-velocity anomaly in the Kaurik Chango Rift, interpreted as a remnant of the oceanic crust, left after the Indotethys Ocean’s closure. In the seismically active Delhi-Haridwar Ridge, a low-velocity upper crustal layer is possibly associated with the sediments of the Indo-Gangetic Plain and with a large number of fault structures. The fragmentation of the Delhi-Haridwar Ridge softens the movement of the Indian Plate to the north, so that the Tethyan Himalaya crust in the area of the Kaurik Chango Fault has remained consolidated and manifests itself as a high-velocity anomaly. The full directory of LOTOS code with data corresponding to this study is available at https://doi.org/10.5281/zenodo.5519210 (accessed on 23 September 2021). •The Indian Plate bends down westwards as it gets closer to the Hindukush Region.•The thickness of the crust varies both across and along the trend of the Himalayas.•The Delhi-Haridwar Ridge softens the movement of the Indian Plate to the north.•There is a remnant of the oceanic crust in the Kaurik Chango Rift.