Uniform slip model underestimates tsunami hazard for probabilistic assessment: results from a case study in the South China Sea

Abstract:

It has long been recognized that rupture complexity, typically in the form of heterogeneous slip distribution pattern, has a significant effect on tsunami wave field. However, the effect of heterogeneous slip distributions is not commonly considered in probabilistic tsunami hazard assessment (PTHA) primarily due to its computational expense. To investigate the effect of heterogeneous slip distribution on PTHAs, we incorporate a stochastic source model into a Monte Carlo-type method for PTHA. Using a hybrid kinematic k-squared source model, we generate a broad range of slip distribution patterns for large numbers of synthetic earthquake events and assess tsunami hazard, as an example, for the South China Sea (SCS). Our result suggests, for a relatively small and confined region like the SCS, the commonly used approach based on the uniform slip distribution fault models could significantly underestimate tsunami hazard, especially on a longer time period. For 500-year return periods, the expected wave height along the coast of west Luzon, Taiwan, southeast China, east Vietnam is generally underestimated by 20-50 %. Notably, the underestimation is more pronounced (some locations reach >50%) for the expected tsunami wave height with a 1000-year return period. Also of note the probability of experiencing 1m tsunami wave in the next 100 years is underestimated by more than 40% in many coastal sites in southeast China and east Vietnam. As the results of PTHA commonly serve as the foundation for further risk assessments, this case study emphasizes how crucial it is to take the effect of rupture complexity into account.