Island morphological influences on landslide-generated tsunami propagation and resonance: A case study in the Xisha Islands, South China Sea

Tsunamis generated by submarine landslides pose significant threats to coastal populations and infrastructure. Their hazards are greatly related to wave propagation processes, such as wave refraction, reflection, and resonance, which can lead to unexpected wave elevations and catastrophic damage. Consequently, a comprehensive understanding of wave propagation and associated influencing factors is essential for enhancing tsunami prediction accuracy and mitigating hazards. In this study, based on the parameter constraints derived from multibeam bathymetric data, we modeled a realistic landslide scenario and associated tsunamis in the Xisha Islands of the South China Sea (SCS) by the coupled models of NHWAVE (Non-hydrostatic Wave Model) and FUNWAVE-TVD (Fully Nonlinear Wave model - Total Variation Diminishing). Through wavelet transform and model decomposition, we concentrated on investigating the energy variations and wave interactions during the wave propagation processes. Additionally, we analyzed the impact of island resonance on tsunami elevation. Our study highlights that landslide-generated tsunamis can excite wave resonance between islands, leading to sustained influence. By decomposing and analyzing the time series data, we identify two components of tsunamis: characteristic component 1 (CC1) and characteristic component 2 (CC2). CC1 is characterized by low-amplitude, high-frequency, short-period waves; conversely, CC2 consists of high-amplitude, low-frequency, long-period waves. CC1 represents the propagated tsunami waves that are directly generated by landslides; whereas CC2 encompasses those influenced by wave refraction and reflection during wave propagation. This study quantifies the contributions of refraction and reflection effects on tsunamis during wave propagation by using variance ratios and the Pearson correlation coefficients. The findings provide quantitative evidence elucidating how island morphologies influence the propagation of landslide-generated tsunamis. This study indicates that submarine landslide-generated tsunami represents a substantial geohazard for the islands, and will be also helpful for the tsunami hazard assessment in the regions where there are complex morphologies (e.g., islands and bays).