Crustal structure beneath northeast India inferred from receiver function modeling

• Crustal structure of northeast India is estimated by using a new inversion approach.
• Moho increases gradually from the Shillong Plateau (SP) to the Lesser Himalaya.
• Average Vp/Vs ratio in SP is less compared to Assam Valley (AV).
• SP and AV show thick upper and middle crust and thin lower crust.
• Lower crust rocks in SP, AV lies between mafic granulite and mafic garnet granulite.

We estimated crustal shear velocity structure beneath ten broadband seismic stations of northeast India, by using H-Vp/Vs stacking method and a non-linear direct search approach, Neighbourhood Algorithm (NA) technique followed by joint inversion of Rayleigh wave group velocity and receiver function, calculated from teleseismic earthquakes data. Results show significant variations of thickness, shear velocities (Vs) and Vp/Vs ratio in the crust of the study region. The inverted shear wave velocity models show crustal thickness variations of 32–36 km in Shillong Plateau (North), 36–40 in Assam Valley and ∼44 km in Lesser Himalaya (South). Average Vp/Vs ratio in Shillong Plateau is less (1.73–1.77) compared to Assam Valley and Lesser Himalaya (∼1.80). Average crustal shear velocity beneath the study region varies from 3.4 to 3.5 km/s. Sediment structure beneath Shillong Plateau and Assam Valley shows 1–2 km thick sediment layer with low Vs (2.5–2.9 km/s) and high Vp/Vs ratio (1.8–2.1), while it is observed to be of greater thickness (4 km) with similar Vs and high Vp/Vs (∼2.5) in RUP (Lesser Himalaya). Both Shillong Plateau and Assam Valley show thick upper and middle crust (10–20 km), and thin (4–9 km) lower crust. Average Vp/Vs ratio in Assam Valley and Shillong Plateau suggest that the crust is felsic-to-intermediate and intermediate-to-mafic beneath Shillong Plateau and Assam Valley, respectively. Results show that lower crust rocks beneath the Shillong Plateau and Assam Valley lies between mafic granulite and mafic garnet granulite.