Deterministic Broadband Ground Motions for the 1905 Kangra earthquake using Multiscale Source Model

The 1905 Mw 7.8 Kangra earthquake was a catastrophic event in Himalayan history, which caused widespread destruction in the near-fault region. This great historical earthquake remains inadequately understood due to the lack of instrumental data. The present study aims to address these gaps by leveraging the spectral element method to simulate ground motions for this historical earthquake. A 3D computational model of the Western Himalayas is developed and validated against recorded velocity time histories of the 2013 Mw 5.8 Bhardawah earthquake, ensuring its accuracy. The developed computational model is employed to generate the velocity time histories of the 1905 Kangra earthquake, nevertheless, they are accurate up to a frequency of 0.5 Hz. Thus, the study simulates broadband ground motions (0.001-20 Hz) for the Kangra event employing a multiscale source model, capturing high- and low-frequency components critical for structural assessment. The simulated results are validated against macroseismic intensity values, offering insights into ground motion characteristics and regional seismotectonics. Peak Ground Acceleration (PGA) contours, plotted for horizontal components ranging from 0.1g to 0.8g and vertical components from 0.1g to 0.6g, reveal maximum ground motions over the Ganga Basin, an effect attributed to the low shear wave velocity of its sedimentary deposits. This study provides the probable ground motions for the 1905 earthquake while elucidating the source mechanism of the Himalayan earthquake, contributing to a robust framework for future seismic hazard assessments in the region.