Himalayan Geology, Vol. 39 (1), 2018, pp. 47-56, Printed in India
Sediment thickness beneath Shillong-Mikir plateau and its adjoining region of northeast India inferred from Teleseismic Receiver Function Modelling
JAYANTA MADHAB BORGOHAIN1,3, KAJALJYOTI BORAH2, DIPOK K. BORA1
1Department of Physics, Diphu Government College, Diphu, Karbi Anglong 782462, Assam, India
2Department of Earth Sciences, Indian Institute of Science Education & Research, Kolkata, Mohanpur 741246, WB, India
3Geophysical Laboratory, Department of Physics, Tezpur University, Tezpur 784028, Assam, India
Email (Corresponding author): dipok23@gmail.com
Abstract: In this study, we carry out detailed analysis of the sedimentary structures beneath the northeastern region (NER) of India, by inverting receiver functions from 9 broadband seismic stations, with applying a well known non-linear and derivative free direct search approach, Neighbourhood Algorithm (NA). Thick sediments (with low shear wave velocities and high Vp/Vs ratio) can amplify seismic waves, which can cause a huge damage due to moderate earthquakes in the region. Results show significant variability of sedimentary layer thicknesses from 0.2-1.0 km beneath the Shillong Plateau, which is the rupture area of great 1897 Shillong earthquake, 0.4-3.1 km beneath the Assam Valley region and 4.1-6.2 km beneath the Lesser Himalayan region. The average sedimentary layer of S-wave velocities for the majority of the stations in the study area varies between ~1.0 and 2.7 km/s with very high Vp/Vs ratio. The Sedimentary structure corresponds to thickness, shear wave velocity and Vp/Vs ratio (Poisson's ratio). Since NER lies in the seismic zone five of the country; these important seismic parameters can be useful in seismic hazard assessment and construction of earthquake-resistant structure to survive from strong earthquake shaking.
Key words: Northeast India; Receiver Function; Shear velocity; Sediment thickness.
