Understanding the physical state and tectonics of Eastern Himalaya using coda wave attenuation

Abstract

Several strong to great earthquakes occurred in northeast India, indicating that the region is seismically very active. For a better understanding of the complex nature of tectonics in the Eastern Himalaya, a frequency-dependent attenuation relation based on coda waves is developed. The backscattering model of Aki and Chouet (J. Geophys. Res. 80: 3322–3342, 1975) is used to study the dependency of coda-Q on lapse time windows and frequency. Analysis of waveforms from 104 local earthquakes recorded by a five-station local seismological network provides frequency-dependent coda-Q relations: Qc = (61±8)f (1.23±0.03) (30s lapse time), Qc = (83±9)f (1.17±0.03) (40s lapse time) and Qc = (104±8)f (1.15±0.04) (50s lapse time). These estimated relationships clearly demonstrate Qc's depth dependency, as longer lapse time windows would carry deeper depth information. Also, the increase in the value of Q 0 (Qc at 1 Hz) with lapse time depicts heterogeneity decrease with depth. The observed quality factor is highly variable with the frequency and lapse time. The higher the value of ‘n,' the more seismically active the region. The observed Qc relation is found equivalent to other similar seismically active regions. © 2023, Indian Academy of Sciences.