Global Geostability Index (GGI): A Pareto-Optimal Multi-Hazard Framework for Long-Duration Civilizational Infrastructure Siting

This paper introduces the Global Geostability Index (GGI), the first systematic multi-hazard geospatial framework designed specifically for 500-year infrastructure planning horizons. Existing indices including the UNDRR Global Assessment Report, INFORM Risk Index, and World Risk Index are calibrated for 5 to 50 year disaster management horizons and are methodologically unsuitable for long-duration civilizational infrastructure siting. The GGI integrates five hazard layers — seismic stability from GEM and USGS hazard models, scenario-based climate refugia from CMIP6 multi-model ensembles, non-stationary flood risk from ISIMIP3b scenario outputs, volcanic exclusion zones from Smithsonian Global Volcanism Program data, and geomagnetic exposure from INTERMAGNET historical records — into a unified screening methodology. The GGI replaces weighted linear combination with Pareto-optimal frontier analysis, eliminating arbitrary weight assignment. Monte Carlo sensitivity analysis across 10,000 Dirichlet-sampled weight combinations demonstrates that 12 candidate regions exhibit robust rank stability regardless of weight perturbation. Flood risk is addressed through scenario-based inundation envelopes acknowledging the non-stationarity critique of Milly et al. 2008. Seismic screening uses PGA as a regional proxy with explicit acknowledgment that site-specific long-period spectral acceleration analysis is required for supertall structural design. All datasets are freely available and all methodology is open-source reproducible. The GGI is offered as a screening framework not a deterministic safety certificate.