Towards a Unified PFDHA Platform: OpenQuake Engine Implementation

Surface fault displacement poses significant risks to critical infrastructure, including dams, pipelines, and nuclear facilities. Despite advances in probabilistic fault displacement hazard assessment (PFDHA) methodologies over the past two decades, the lack of unified, open-source computational platforms has hindered standardized application and reproducibility. This study presents a comprehensive PFDHA framework integrated within the OpenQuake Engine, providing a standardized platform for fault displacement hazard calculations.

The framework follows the earthquake approach proposed by Youngs et al. (2003), implementing four interchangeable computational modules: (1) primary surface rupture probability, (2) primary fault displacement, (3) secondary surface rupture probability, and (4) secondary fault displacement. This modular architecture enables flexible model selection and facilitates sensitivity analyses across different modeling assumptions.

The implementation integrates state-of-the-art models from diverse sources: models developed through the Fault Displacement Hazard Initiative (FDHI), global empirical regressions derived from updated worldwide databases, region-specific models calibrated for Japan, Australia, and the Western United States, and physics-based numerical approaches. The comprehensive model library comprises 25 models across four categories, validated against International Atomic Energy Agency (IAEA) benchmarking studies and applicable to normal, reverse, and strike-slip faulting mechanisms.

The framework produces hazard curves expressing annual frequency of exceedance versus displacement amplitude, and hazard maps depicting spatial distribution of displacement at specified return periods. Application to the Calabria region of Italy, including critical dam sites, demonstrates the platform's capability to assess both principal and distributed displacement hazards for infrastructure. Results highlight the dominant contribution of principal faulting near fault traces and the sensitivity of hazard estimates to model selection.

This work represents a significant step toward establishing a standardized, transparent, and reproducible platform for PFDHA, addressing the current lack of unified computational tools in the seismic hazard community.