Probabilistic Tsunami Risk Assessment and Cost-Benefit Analysis of Seawall Adaptation Strategies: A Case Study of Coastal Chile

Tsunamis pose severe threats to the infrastructure and economies of coastal nations, particularly in Chile, where high seismic activity intersects with concentrated coastal populations and economic assets. Despite the rising risks, current risk assessment frameworks often overemphasize hazard metrics, such as occurrence probability and run-up height, while neglecting the comprehensive integration of economic vulnerability. Furthermore, existing research on adaptation strategies predominantly focuses on the local engineering design of seawalls, lacking systematic, regional-scale cost-benefit analyses (CBA). This limitation hinders the comprehensive evaluation of adaptation measures and restricts the scientific basis for disaster mitigation policymaking.

This study establishes a comprehensive probabilistic risk assessment framework that integrates vulnerability and economic exposure. By generating a stochastic earthquake event set and utilizing the COMCOT numerical simulation model, we constructed a risk model that accounts for multidimensional economic factors. Validation results demonstrate that incorporating vulnerability significantly mitigates the overestimation inherent in single-exposure assessments, aligning the results closer to historical observations and improving estimation accuracy by 150.13%.

The results exhibit significant spatial heterogeneity in risk distribution. Spatially, risk is concentrated in the central region, exceeding levels in the north and south. Notably, a divergence exists between relative and absolute risk hotspots within the central area: Coquimbo exhibits the highest relative impact (2.69% of regional GDP), whereas Valparaíso incurs the highest absolute risk, with an Annual Average Loss (AAL) of US$380 million. These findings establish the quantitative benefit baseline for the subsequent cost-benefit analysis.

Based on this framework, we evaluated the economic feasibility of regional seawall strategies under various scenarios of economic development and investment costs. The results indicate that future average benefits under the "Economic Development" scenario are approximately double those of the "Economic Stagnation" scenario, with benefit fluctuations ranging from 1.5 to 2.5 times. Under current economic conditions with low investment costs, seawall construction is feasible in eight regions; however, feasibility diminishes as investment costs rise. Notably, in an "Economic Stagnation" scenario combined with medium-to-high investment costs, no regions present economically feasible solutions. This research fills a critical gap in regional-scale economic evaluations of adaptation strategies, providing a robust decision-support tool for tsunami disaster risk reduction.