Scenario-based seismic risk assessment for buried transmission gas pipelines at regional scale

Buried gas pipelines in seismic-prone regions may suffer leaks or breaks as a consequence of an earthquake, especially if the pipeline is subjected to large differential displacements due to geotechnical failures (e.g., landslide or liquefaction). This paper presents a methodology to assess the risk of a gas pipeline infrastructure at a regional level in the aftermath of a seismic event. Once earthquake characteristics, such as magnitude and epicenter, are known, seismic intensity measures (IMs), such as peak ground acceleration (PGA) and peak ground velocity (PGV), are estimated at the location of each pipe through a simulation-based procedure. The potential updating from real-time data coming from accelerometric stations is considered. These IMs are then used to study the cascading landslide and liquefaction hazards, providing a hybrid empirical-mechanical-based estimation of permanent ground displacements (PGD). With the aid of damage and fragility functions from the literature, loss figures and damage maps are derived as decision-support tools for network managers and stakeholders. Losses provide a preliminary estimation of repair costs, whereas damage maps support the prioritization of inspections in the aftermath of the event. The risk methodology is a novel combination of cutting-edge and consolidated approaches. Firstly, different crosscorrelation models between PGA and PGV are included. Secondly, a new three-phase back-to-back geotechnical approach is provided for both landslide and liquefaction, representing (1) the susceptibility, (2) the triggering, and (3) the PGD estimation phases. The 1976 Friuli earthquake and the high-pressure gas network of northeast Italy are used as a test-bed scenario for the risk methodology aimed at emphasizing pros and cons of the different alternative options investigated.