Assessment of weathered rock effects on local seismic hazard using 2D dynamic numerical modeling: a case study of the Bukit Timah granite, Singapore

This study evaluates the seismic impact of the Bukit Timah granite massif in Singapore, emphasizing the role of granite weathering in local site effects. A 2.5D geomodel was constructed using geophysical data, boreholes, and geological maps, from which five 2D cross-sections were extracted for dynamic numerical modeling. Simulations were performed to assess resonance frequencies, amplification patterns, peak ground acceleration (PGA), and shear wave velocity (Vs). The dominant frequency ranged between 1.8 and 3.8 Hz, with amplification factors up to 4.5, consistent with HVSR data. The close agreement between HVSR and modeling results highlights the influence of weathered granite layers on site response. A 2D Vs model was derived from the inversion of HVSR and synthetic curves. The findings provide detailed insights into lithological and topographic effects, especially lateral heterogeneities in weathering. This study demonstrates the reliability of numerical modeling for microzonation in granitic terrains and supports its use in enhancing seismic risk assessments and urban planning in weathered rock regions.