Preliminary Seismic Hazard and Exposure Assessment of the Lombok Strait Strike-Slip Faults: A Comparative Analysis of the Mw 7.5 Southern and Mw 7.6 Northern Segments in Lombok Island
Abstract
Lombok Island is situated within a complex tectonic environment shaped by subduction, back-arc thrusting, strike-slip faulting, and heterogeneous crustal structures. Despite this complexity, the ground-motion and population-exposure implications of the offshore Lombok Strait Strike-Slip Faults remain relatively understudied. This study presents a preliminary assessment of seismic hazard and population exposure associated with two offshore strike-slip fault scenarios derived from the 2024 Indonesian seismic-source framework (PuSGeN): an Mw 7.6 northern-segment scenario and an Mw 7.5 southern-segment scenario. Using the OpenQuake Engine and the Boore et al. (2014) ground-motion prediction equation, the study estimates Peak Ground Acceleration (PGA) and Modified Mercalli Intensity (MMI), which are spatially overlaid with high-resolution WorldPop 2026 population estimates to quantify and characterize population exposure across Lombok. The results indicate substantial differences in regional hazard severity and population exposure. The Mw 7.5 scenario yields a maximum PGA of 0.14g, with 99.3% of the population of Lombok experiencing light to moderate shaking (MMI IV-V). In contrast, the Mw 7.6 scenario produces PGA values up to 0.59g (MMI VIII) in Central Sekotong, exposing approximately 2.64 million people (65.65% of the total population) to strong, very strong, or severe shaking (MMI VI-VIII). Additionally, a transect line analysis identified significant spatial ground-motion amplification attributable to local geological site conditions. Ground motion increased by up to 19.83% in Mataram City and by 23.56% near Tanjung based on the Mw 7.6 scenario. These findings complement existing research on the Flores Back-Arc Thrust and other regional earthquake sources nearby Lombok, offering initial insights into the significance of oceanic strike-slip faulting for future earthquake hazard and risk assessment throughout the island.