Seismic risk expresses the expected degree of damage and loss following a catastrophic event. An efficient tool for assessing the seismic risk of embankments is fragility curves. This research investigates the influence of embankment's geometry, the depth of rupture occurrence, and the underlying sandy soil's conditions on the embankment's fragility. To achieve this, the response of three highway embankments resting on sandy soil was examined through quasi-static parametric numerical analyses. For the establishment of fragility curves, a cumulative lognormal probability distribution function was used. The maximum vertical displacement of the embankments' external surface and the fault displacement were considered as the damage indicator and the intensity measure, respectively. Damage levels were categorized into three qualitative thresholds: minor, moderate, and extensive. All fragility curves were generated for normal and reverse faults, as well as the combination of those fault types (dip-slip fault). Finally, the proposed curves were verified via their comparison with those provided by HAZUS. It was concluded that embankment geometry and depth of fault rupture appearance do not significantly affect fragility, as exceedance probabilities show minimal differences (<4%). However, an embankment founded on dense sandy soil reveals slightly higher fragility compared to the one founded on loose sand. Differences regarding the probability of exceedance of a certain damage level are restricted by a maximum of 7%.

Fault rupture propagation through near-surface soil deposits and the anticipated damage on adjacent structures have been thoroughly investigated focusing on single fault rupture. Nevertheless, large secondary faults have also been observed in field investigations. For this reason, the development of contemporaneous fault ruptures -and the resulting soil displacements-caused by complex combinations of oblique-slip main and non-parallel secondary faults is investigated herein. Moreover, the response of buried steel pipelines crossing such geohazardous areas is also examined aiming to assess pipeline vulnerability due to the presence of secondary faults. The investigation is conducted utilizing a decoupled numerical methodology, in which soil displacements are calculated utilizing a 3D numerical model, and subsequently, they are applied to a separate numerical model for the assessment of pipeline distress. Useful conclusions are drawn regarding the developed fault rupture patterns and the sequent pipeline distress under such detrimental conditions that may occur in seismotectonic regions.