Identifying the needs and future directions of seismic hazard for probabilistic infrastructure risk analysis

The vulnerability of urban infrastructure to both ground shaking and geotechnical failure during large earthquakes has been demonstrated by recent earthquakes such as the 2010 2011 Canterbury earthquake sequence (New Zealand, 2010 2011) or 2010 Haiti event. Probabilistic seismic risk analysis to infrastructure systems requires the characterisation of both the transient shaking and permanent ground deformation elements of the hazard, and must do so incorporating both the aleatory and epistemic uncertainties and the spatial correlations and dependencies that are inherent in both of these aspects. Recent developments in characterisation of spatial correlation and cross-correlation in the ground motion uncertainties form the foundations of a comprehensive Monte Carlo-based methodology for analysis of seismic risk to spatially extended systems. New research directions are needed, however, in order to ensure that secondary hazard aspects are incorporated in the same way. These include the treatment of site amplification of the ground shaking, the modelling of permanent ground deformation from slope displacement and liquefaction, and permanent displacement due to coseismic slip on and around the fault rupture. Key considerations for integrated probabilistic framework for physically-realistic characterisation of the ground shaking and permanent ground displacement are illustrated using the example of simulation spatially correlated fault slip on an active fault rupture in a manner that can be integrated within a Monte Carlo-based probabilistic seismic hazard methodology. Probabilistic analysis of seismic risk is the most common methodology used by organisations responsible for maintaining infrastructures to make informed decisions based on the cost to benefit ratios of particular mitigation strategies. But analysis of infrastructural risk presents new challenges to both the hazard and risk modellers to provide models of ground shaking and permanent ground displacement that can be applied to spatially extended and interconnected systems. A single infrastructural system is dependent on many elements over an extended geographical region, and the performance of the system or systems may depend on the location of greatest damage. Further compounding the complexity is the fact that a single infrastructural system is composed of fragile elements that may respond dissimilarly according to different characteristics of the hazard. One example might be a gas network in which mechanical elements may be most adversely affected by high frequency acceleration, storage systems and pumping stations by low frequency ground motion, whilst underground pipes may be most at risk from permanent ground displacement due to geotechnical failures. This paper outlines some of the main challenges facing the seismic hazard modeller in order to provide hazard input into probabilistic seismic risk analysis for interconnected and spatially extended infrastructures. Focus is placed on four critical elements: ground shaking, site amplification, geotechnical failure due to land-sliding and liquefaction, and finally co-seismic displacement due to rupture on the fault surface. A summary of current approaches for characterising each of these elements