Attenuation of regional seismic Lg waves and its spectral characteristics in and around the Indo-Burman Ranges of North Eastern region of India

Abstract

The propagation characteristics of crustal Lg waves have been investigated in and around geotectonically complex Indo-Burman Ranges (IBR) of North Eastern region (NER) of India. To cater towards seismic hazard assessment and civil engineering practices, Lg attenuation has been studied by determining the regional average quality factor (QLg) in the frequency range of 0.5–5 Hz. The Lg attenuation regional model for IBR and its vicinity areas devised is given as $$Q_{Lg} = (407 \pm 0.00082)f^{{\left( {1 \pm 0.1864} \right)}}$$. The attenuation coefficient (Q0 = 407) in the model represents a moderately attenuating lithosphere in the study area. The power of frequency dependence (η = 1) is indicative of the fact that Lg attenuation in IBR and its adjoining areas is not only highly frequency dependent, but also the tectonic activity in IBR is currently high. Frequency dependence of Lg attenuation indicates that scattering mechanism plays a dominant role in attenuation of Lg waves. This is possible when the lithosphere beneath is highly heterogeneous in nature which is caused due to the subduction tectonics of IBR. A scrutiny of the corner frequencies (fc) in the Lg spectra has indicated the role of path and site effects in the scattering of Lg energy. Predominant frequency of Lg in IBR has been observed to be around 2 Hz, which falls within the natural frequency range of common structures (1–10 Hz) which may be a concern for civil engineering safety. This Lg attenuation model will be helpful in the prediction of ground motion, and will play a pivotal role in adopting a suitable seismic coefficient for civil engineering designs in order to mitigate seismic hazard in the IBR and its nearby areas in NER of India.