LAUSR

Abstract The Indian Ocean region is one of the challenging areas for seismological research because of its complex seismotectonic settings and intricate structural heterogeneity prevails beneath the Indian Ocean region. In order to address the problem we attempted to determine the attenuation structure for the Indian Ocean region using coda wave generation by single backscattering model. In this study, the central frequency of interest has been considered between 1.5 and 12.0 Hz with lapse time window (LTW) of 20, 30, 40, 50 and 60 s measured from the origin time of the earthquake. We obtained the attenuation relation for different seismotectonic zones associated with varying estimate of attenuation parameters; Spreading Zone [Qc(SPZ) = 171f1.10]; Subduction Zone [Qc(SZ) = 220f0.961]; Triple Point Junction [Qc(TPJ) = 156f1.15]; Prominent faults of Indian Ocean region [Qc(PFIOZ)= 197f0.99] and Volcanic and Hotspot [Qc(VZ,HS) = 209f0.97]. We estimated average frequency-dependent attenuation parameters of Q0 that varies as 156 ± 32 ≤ Q0 ≤ 220 ± 33 with corresponding variability in frequency parameter (θ) as 0.96 ± 0.05 ≤ θ ≤ 1.15 ± 0.09 at 40 s LTW for the entire Indian Ocean region, suggesting that the entire Indian Ocean is seismo-tectonically highly active and is attributed to the nature and extent of attenuation due to varying amount of structural heterogeneity in different tectonic zones characterized by the occurrence of earthquakes of varying strengths in the seismically active tectonic zones of the region. We found that the triple Junction (RTJ) is associated with low-Qc and high attenuation because of deposition of a variety of sediments at the RTJ, which is in unison to the geological mapping of the region. We observed that our estimated attenuation model is comparable that of the Aleutian Islands (the Adak Seismic zone) at low frequency (≤5 Hz) and to the Philippine Sea Subduction zone (Petukhin) at higher frequency range (≥5 Hz), which is very much correlative to seismo-tectonic settings. We infer that our assimilated attenuation model has potential to provide information on intricate seismotectonics and seismogenesis for computing earthquake source parameters, and earthquake hazards that may be useful for assimilating detailed seismic velocity structure beneath the Indian Ocean region.