Consideration of near-field directivity effects in probabilistic seismic hazard assessment: a case study over North–East India
摘要
This study presents a probabilistic seismic hazard assessment (PSHA) for the North–East Indian region, incorporating the near-field directivity effects into the analysis. Near-field effects, characterized by intense velocity pulses and low-frequency content, significantly influence ground motion behavior in close proximity to fault ruptures. Utilizing the two established frameworks for the near-field effects, a logic tree approach is adopted to compute hazard curves, uniform hazard spectra (UHS), and hazard maps with and without near-field effects. The analysis is performed for site class B (Vs30 760–1500 m/s) conditions and two return periods: 2475 years (2% probability of exceedance in 50 years) and 475 years (10% probability of exceedance in 50 years). Contour maps of directivity adjustment factors, developed for selected faults, demonstrate the amplification range and spatial extent of near-field effects, which extend up to 30 to 50 km around the faults and up to 300 km in the strike-parallel direction for the strike-slip faults. The results also indicate that near-field amplification factors vary between 1.2 and 2.0 at T* = 8 s, with significant spatial variation depending on the fault type and location. The findings highlight the importance of incorporating near-field effects in seismic hazard assessments to improve the accuracy of hazard estimates for critical infrastructure in the North–East Indian region.