Earthquake Analysis Requirement for Fixed Offshore Structures, Offshore Malaysia

Abstract

Malaysia has always been considered as a non-earthquake zone. For offshore Malaysia, the only guidance document on earthquake is ISO 19901-2 which put Malaysia as a Zone 0. However, this perception changes after the big earthquake in Acheh, Indonesia (2004), and recently in Sabah, Malaysia (2015). To ensure the safety of its offshore facilities, PETRONAS has appointed D'Appolonia to conduct a Probabilistic Site Hazard Assessment, PSHA study post Acheh earthquake to determine the earthquake spectral response value to be used for its offshore structures design. Due to the perception that D'Appolonia PSHA spectral response value is on the high side, Universiti Teknologi PETRONAS, UTP was later tasked to conduct another round of PSHA study to complement D'Appolonia findings. The spectral response values from ISO 19901-2 and results from D'Appolonia and UTP PSHA studies were then compared and validated. This paper discusses the process on how PETRONAS developed the design requirement due to earthquake for structures located offshore Malaysia, starting with Probabilistic Site Hazard Assessment, PSHA based on historical data of seismic events in South East Asia and mapping of all relevant crustal faults, and later map the seismic contours to the local soil condition offshore Malaysia to develop the spectral response map, and later the response spectrum for shallow and deep foundations to be used for the earthquake analysis for its facilities offshore Malaysia.