Site-Specific Surface PGA Assessment Via Site Response Analysis for the SOGIP Area, Sipitang, Sabah

This paper presents a site-specific assessment of Surface Peak Ground Acceleration (PGA) for the Sabah Oil and Gas Industrial Park (SOGIP) located in Sipitang, Sabah, Malaysia, motivated by increasing seismic activity in the region and the limitations of regional-scale seismic hazard maps in representing local ground conditions for critical infrastructure. Regional PGA estimates commonly assume uniform subsurface conditions and may therefore underestimate or overestimate seismic demand at specific sites, underscoring the need for localised evaluation that accounts for geological and geotechnical variability. The study uses subsurface data from 23 boreholes distributed across the project area, with borehole logs interpreted to establish stratigraphic profiles and engineering soil properties influencing seismic wave propagation. Site classification was carried out in accordance with MS EN 1998-1:2015 (Malaysia National Annex to Eurocode 8) to determine soil categories and associated amplification characteristics. Equivalent-linear seismic site-response analyses were subsequently performed using DEEPSOIL to model ground-motion amplification from bedrock to the ground surface under varying seismic input motions. Prior to spatial averaging based on borehole cluster locations, the computed results indicate that surface PGA values range from 0.0137g to 0.0552g when adopting a reference bedrock PGA of 0.02g. For higher reference, bedrock PGA values of 0.03g, including rationalised inputs of 0.027g and 0.031g, yield surface PGA values between 0.0153g and 0.0821g. These calculated values exceed the existing regional seismic hazard map for Sipitang, which indicates bedrock PGA values of approximately 0.010g–0.020g for a 475-year return period, demonstrating significant local site amplification effects governed by subsurface conditions. The findings emphasise the importance of conducting site-specific seismic hazard assessments for major industrial developments to improve seismic design parameters, support disaster risk mitigation strategies, and enhance structural resilience in rapidly developing seismic-prone of Sabah

Site response analysis, Surface PGA, Seismic hazard, SOGIP, Sipitang, Sabah, Borehole data, Ground motion amplification

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