Integrated multi hazard and site effect assessment for the greater Shillong region Northeast India from a geocartographic perspective

The Shillong Plateau, one of the most seismically active zones of South Asia, offers a unique setting for integrated assessment of multi-hazard interactions and local site effects. This study develops a geocartographic framework that combines detailed tectonic, geological, geomorphological, borehole and topographic information with resonance-frequency estimates from ambient noise and earthquake-based receiver-function analyses to derive spatially explicit hazard and site-effect maps for the Greater Shillong region. Using 10 deep borehole logs and two cross-sections (AB and CD), the subsurface stratigraphy is constrained up to depths exceeding 250 m and linked to lateral variations in fundamental frequency, which range from about 3–8 Hz. The hitherto geophysical profiles (AB and CD) provide contrasting impedance structure and amplification potential. Further, the resonance-frequency estimates are correlated with elevation and slope. This leads to delineation of zones where topographic amplification coherently reinforces, or decouples from, impedance-driven site response. In contrast to previous works, this work delivers an integrated, map-based characterization of sediment thickness, shear-wave velocity structure, resonance frequency and topographic modulation that refines the spatial pattern of seismic susceptibility and identifies pockets of potentially high vulnerability within the Shillong urban corridor. The results demonstrate considerable level of heterogeneity. Overall, the findings stemming from coupling multi-source geodata with passive and earthquake-based measurements for regional-scale seismic microzonation offer valuable information for guiding land-use planning and disaster risk reduction in tectonically active plateaus.