Lg wave attenuation of Northeast India Archaean as a new standard for Earth's most seismic regions

Physical modeling of Lg-wave attenuation is used in designing resilient and safer civil engineering structures and is thus vital for seismic hazard mitigation. I here report an attenuation model for one of the most active seismic sources of Himalayas-determined Northeastern region (NER) of India—the Eastern Shillong Plateau–Mikir Hills (ESPMH) tectonic domain—based on four well-constrained regional crustal earthquakes between 2007–2011. Frequency-dependent attenuation of Lg wave has crustal quality factor QLg≈48.92±1.08 and its frequency dependency of η≈0.97±0.16. The model is strictly high-frequency dependent (η=0.97), indicating that Lg attenuates dominantly by the scattering mechanism. The attenuation becomes critically high around the frequency of 0.5 Hz, the same as in the most tectonically active regions of the world. The extra low value of Qo=48.92 is the lowest reported from any continental part of our planet, which reveals a most attenuative Earth's crust posing a high seismic threat. As the results imply an extensive, seismically potentially destructive presence of melts/aqueous phases in Earth's crust, the probability of a damaging earthquake in and around ESPMH is non-negligible. Multiple additional factors contribute to the gross attenuation of Lg, as it is reasonable to account for the anomalously high attenuation in the NER Archaean as dominantly lithologically hardest and Earth-oldest terrane, making the new model pertinent to Earth's tectonically most active regions.         ARK: https://n2t.net/ark:/88439/x055006 Permalink: https://geophysicsjournal.com/article/357 Reprints & Permissions