Source Parameters and Scaling Relations for Moderate Size Earthquakes in North–East India Region

The present study estimates source parameters and proposes scaling relationships for moderate size earthquakes (mb 3.7–5.8) in seismically active North–East India region. The study is based upon the spectral analysis of high-quality waveforms comprising of P- and S-waves obtained from strong ground motion (SMA) records of 50 earthquakes that has occurred in the region. A two-step procedure is adopted to estimate the earthquake source parameters. It has been observed that the average seismic moment and source radii vary from 1.05 × 1015 to 1.99 × 1017 N-m and 500 to 2000 m, respectively. The average corner frequency ratio [fC(P)/fC(S)] of P-wave and S-wave is found to be 1.2, which shows the shift in the corner frequency. The total estimated energy varies between 9.22 × 1010 and 1.42 × 1014 J, while the average stress drop varies from 1.8 to 29.4 MPa. One of the major outcome of this study is that the stress drop does not vary significantly with the magnitude and self-similarity exist among the earthquakes in North–East India region. The scaling relation between the seismic moment and the corner frequency is Mofc3=1.35×1017N- ms-3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ M_{\text{o}} f_{\text{c}}^{ 3} = 1.35\; \times \; 10^{17} N{\text{ - ms}}^{ - 3} $$\end{document}. The median stress drop value for NE India region is found to be about 9.2 MPa. The earthquake source parameters and the scaling relations developed in this study will be useful for carrying scenario based seismic hazard analysis studies in the NE India region.