Assessment of seismic hazard in the Thai offshore oil industry: a case study

Thesis Abstract

Offshore oil operations in the Gulf of Thailand are exposed to seismic hazards that threaten structural integrity, operational continuity, environmental safety, and economic resilience. The study addresses the gap in sector-specific seismic risk characterization by integrating geophysical, geological, and engineering perspectives to inform hazard assessment and risk mitigation for Thai offshore assets. The aim is to develop a comprehensive seismic hazard profile for the Thai offshore oil industry and to propose a framework for risk-informed decision-making in siting, design, and emergency planning. Specific objectives are (i) to characterize regional seismicity and magnitudes, focal mechanisms, and recurrence intervals using historical catalogs and recent instrument deployments; (ii) to evaluate propagation of seismic waves through the Gulf of Thailand marine basin and near-field basin responses via probabilistic seismic hazard analysis (PSHA) and site response modeling; (iii) to assess the vulnerability of offshore platforms and subsea installations through structural performance simulations under stochastic earthquake scenarios; (iv) to identify critical failure modes and cascading risk pathways linking seismic events to operational downtime and environmental impact; and (v) to develop a decision-support framework for hazard mitigation that balances safety, cost, and regulatory compliance. The methodology adopts a mixed-methods, theory-driven design combining quantitative probabilistic seismology with qualitative risk assessment. The population includes offshore platforms, subsea templates, and moored installations operated by Thai national and international firms in the Gulf of Thailand. A sample set of 12 representative installations is selected to reflect varying depths, structural typologies, and proximity to active fault zones. Data collection instruments comprise (a) seismic catalogs from Thai Meteorological Department and international agencies (1960–2024) for PSHA inputs; (b) ambient noise and site response measurements from deployed ocean-bottom seismometers and a temporary land-based array; (c) structural performance data from platform design specifications, maintenance records, and historical inter-event downtime; (d) stakeholder interviews with safety engineers and operations managers to capture risk perceptions and regulatory constraints. Validity and reliability are ensured through cross-validation of seismic parameters with independent catalogs, calibration of site response models with measured data, and triangulation of interview findings with archival records. Analytical methods include PSHA to compute annual frequency of exceedance for spectral accelerations across key return periods, and finite-element structural analyses to simulate platform and subsea structure responses under representative ground motions. Site amplification factors are derived using probabilistic site response modeling integrated with basin-depth corrections. Regression analyses examine relationships between seismic intensity and historical downtime, while Monte Carlo simulations propagate uncertainties in earthquake occurrences, ground motions, and structural vulnerabilities to estimate potential loss of function and environmental risk. A conceptual model linking regional tectonics, seismic hazard, engineering resilience, and operational risk is employed to interpret results. The study also utilizes scenario-based risk assessment to inform emergency response planning and business continuity strategies. Expected findings include (i) a refined seismic hazard curve for Gulf of Thailand offshore structures highlighting dominant return periods and site-specific amplification effects; (ii) identification of critical installations with elevated vulnerability to soil-structure interaction and near-field effects; (iii) quantified risk estimates for downtime, repair costs, and environmental incident probabilities under simulated seismic sequences; (iv) a prioritized set of mitigation measures, including enhanced foundation design, redundancies in critical systems, and revised inspection intervals; and (v) a decision-support framework that integrates PIR (probability–impact–risk) matrices with regulatory requirements. The study contributes to knowledge by bridging regional tectonics, marine geophysics, and offshore structural engineering to produce a tailored seismic hazard framework for the Thai offshore oil sector. It offers methodological innovations in integrating PSHA with site-specific structural vulnerability assessments and stakeholder-driven risk prioritization. Findings are expected to inform regulatory policy, platform lifecycle planning, and emergency preparedness programs. The main conclusion will emphasize the necessity of adopting risk-informed design and adaptive management strategies for seismic resilience, while recommendations will focus on enhancing monitoring networks, updating design standards to reflect site effects, implementing targeted retrofits for high-risk installations, and formalizing an industry-wide seismic hazard reporting protocol to underpin continuous improvement in offshore safety and environmental protection.