Dual risk-targeted seismic and tsunami hazard assessment for western Makran coasts, southeast Iran

This study presents a comprehensive assessment of multi-hazard seismic and tsunami risks along the western Makran coastline, originating from earthquakes in the Makran Subduction Zone (MSZ). As infrastructure development intensifies in this region, a combined risk assessment of seismic and tsunami hazards becomes paramount. A holistic approach integrates probabilistic seismic hazard assessment (PSHA) and probabilistic tsunami hazard assessment (PTHA) using Boolean logic rules to evaluate cumulative damages. Fragility curves based on peak ground acceleration (PGA) for seismic ground motion and median peak momentum flux (PMF) for tsunami intensity measures are employed. Over 1700 earthquake scenarios in the MSZ are modeled, revealing that seismic and tsunami hazards increase from west to east along the coastline. The uniform hazard calculated PGA and peak tsunami amplitude (PTA) values for a return period of 2475 years reach 0.6 g (for the easternmost point of the Makran coast in Iran) and 8.5 m in Chabahar, respectively. Combined seismic and tsunami risks are evaluated for structures such as concrete moment frames (CMF) and unreinforced masonry bearing walls (URML). Results indicate a 35.3% risk of moderate or greater damage to URML buildings over 50 years in high-risk areas like Chabahar, due to cascading seismic and tsunami events. A comparison of results with Oregon Seaside in the Cascadia Subduction Zone (CSZ) shows higher seismic-induced damage and lower tsunami-induced damage in Oregon compared to Makran, due to distinct seismic and tsunami hazard curves and bathymetric conditions. Using a risk-targeted approach for a 1% probability of failure risk over 50 years (ν(F) = 2 × 10−4) and equivalent to a 10% structural failure probability (P_F (IM = im) = 0.1), the maximum calculated PGA, PTA, and PMF values along the Makran coastline are estimated at 0.46 g, 7.6 m, and 275 m3/s2, respectively. The study introduces a dual risk-targeted approach, calculating pairs of ground motion and tsunami intensity parameters for specific failure probabilities to generate risk curves for structural design. Results highlight a significant underestimation of design parameters when dual risk-targeted approaches are not considered. The integration of multi-hazard seismic and tsunami risk assessments, along with the dual risk-targeted approach, provides valuable insights for policymakers and stakeholders in coastal resilience planning.