The segmented East Indian continental margin developed after the Early Cretaceous break-up from Antarctica. Its continental crust terminates abruptly without considerable thinning along the Coromondal strike-slip segment and thins considerably before it terminates in the orthogonal rifting segments. The segments have an exhumed continental mantle corridor oceanwards of them. This, proto-oceanic crust, corridor varies in width from segment to segment, indicating a relationship with varying break-up-controlling tectonics of the adjacent margin segments.The top of the proto-oceanic crust is imaged by a higher reflectivity zone, while its base does not have any distinct signature. A contorted system of reflectors represents its internal structure. Its gravity signature is a longer-wavelength anomaly with peak values up to 30 mGal less negative than surrounding values. Its magnetic signature is represented by a positive anomaly with peak values of 0–56 nT. Wide proto-oceanic segments are adjacent to margin segments that are preceded by the orthogonally rifting Cauvery, Krishna–Godavari and Mahanadi rift zones. A narrow proto-oceanic segment is adjacent to the margin segment initiated by the dextral Coromondal transfer zone. A combination of seismic interpretation and gravity/magnetic forward modelling indicates that proto-oceanic crust is most probably composed of lower crust slivers and unroofed hydrated upper mantle, being formed between the late rifting and the organized sea-floor spreading.

We use local earthquake coda waveform to characterize the seismic attenuation across northeast India. We measure temporal decay of coda amplitude to estimate coda quality factor (Qc) at frequencies 1 to 14 Hz and abstract Q0 and its frequency dependence (η). Single‐trace measurements reveal similar average Qc between 1 and 3 Hz and significant variation at higher frequencies. We combine single‐trace Qc measurements into a backprojection algorithm to compute 2‐D Qc tomography maps. The Qc maps reveal strong correlation with tectonic settings. At low frequencies (1–5 Hz) we observe relatively lower Qc in the Sikkim and Eastern Himalaya, southern Tibetan Plateau, and Bengal Basin, while the intraplate region and Indo‐Burman subduction zone have higher Qc. At higher frequencies (>5 Hz) we observe pronounced low Qc beneath Sikkim Himalaya, relatively lower Qc in the intraplate region and relatively higher Qc in the Bengal Basin and Indo‐Burman subduction zone. We compare our Q0 map with Vs tomography to characterize the crust. The lateral variation in the structure of the Himalayan thrust sheets between Sikkim and Eastern Himalaya is highlighted by low and intermediate Q0, respectively. The southern Tibetan Plateau, known to have low Vs due to elevated crustal temperatures, is characterized by low Q0, indicating associated scattering and anelastic effects. The intraplate continental crust and the cold elastic subducting oceanic lithosphere have intermediate‐to‐high Vs and are marked by high Q0. The Bengal Basin, with thick low Vs sedimentary layers overlying a rift‐faulted high Vs transitional crust, has low‐to‐intermediate Q0 due to depth averaging of attenuation characteristics.

The Coulomb failure stress (CFS) criterion is the most commonly used method for predicting spatial distributions of aftershocks following large earthquakes. However, large uncertainties are always associated with the calculation of Coulomb stress change. The uncertainties mainly arise due to nonunique slip inversions and unknown receiver faults; especially for the latter, results are highly dependent on the choice of the assumed receiver mechanism. Based on binary tests (aftershocks yes/no), recent studies suggest that alternative stress quantities, a distance-slip probabilistic model as well as deep neural network (DNN) approaches, all are superior to CFS with predefined receiver mechanism. To challenge this conclusion, which might have large implications, we use 289 slip inversions from SRCMOD database to calculate more realistic CFS values for a layered half-space and variable receiver mechanisms. We also analyze the effect of the magnitude cutoff, grid size variation, and aftershock duration to verify the use of receiver operating characteristic (ROC) analysis for the ranking of stress metrics. The observations suggest that introducing a layered half-space does not improve the stress maps and ROC curves. However, results significantly improve for larger aftershocks and shorter time periods but without changing the ranking. We also go beyond binary testing and apply alternative statistics to test the ability to estimate aftershock numbers, which confirm that simple stress metrics perform better than the classic Coulomb failure stress calculations and are also better than the distance-slip probabilistic model.

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