Source parameters and scaling relations for small to moderate earthquakes in the Indo-Burma Ranges, North-east India, and its seismotectonic implications

The Indo-Burma Ranges (IBRs) and its surrounding North-east India is one of the seismotectonically active subduction systems in the world, where the Indian Plate is subducting beneath the Sunda Plate. This has resulted in major earthquakes in the past. In this study, spectral analysis of S-wave has been used to investigate the source parameters for local earthquakes (3.3 ≤ M_D ≤ 5.8) exclusively in the Indo-Burma region fusing a network of six stations by adopting the Brune model. The corner frequencies (f_c) of the events are varied from 0.6 to 3.2 Hz. The estimated source parameters lie in the range from 9 × 10¹³–3.7 × 10¹⁷ N m, 0.2–35.1 MPa, 410–1,956.4 m, 0.002–1.196 m, and 2.9–13.5 Hz for seismic moment M₀, stress drop (Δσ), source radius, source dislocation, and maximum cut-off frequency (f_max), respectively. The scaling relation between M₀ and f_c has been derived as M₀ = 1.622 × 10¹⁶ f_c^−5.298. The scaling relations of M₀ with f_max and stress drop have also been derived. The high-stress drops (>10 MPa) were at a depth zone of ~40–60 km, while the stress drops were less than 4.0 MPa beyond this depth, indicating the shallow and deeper portion of the lithosphere to be relatively brittle. We postulate that this could occur due to a complex detachment process as a result of slab tearing in the region. The upper boundary of stress drop was found to have an increasing trend with the focal depth of the earthquakes. The empirical relations between M₀ − M_D and M_W − M_D have also been derived for the IBRs. The estimated source parameters and scaling relations will be useful in estimations of lithospheric strength, simulation of strong ground motion in the IBRs, and calibrating the coefficient of the local earthquakes in the IBR and its surrounding region.