LONG-TERM SEISMIC RISK ASSESSMENT CONSIDERING THE TRIGGERED AFTERSHOCKS

Assessment of the long-term risk profile considering the triggered seismic sequence is ren-dered complicated by the short-term clustering of aftershock events following the main event and the increased potential for damage accumulation. The assessment of long-term seismic risk profile for the main seismic events is based on the renewal of the structure to a pre-scribed state after each seismic event. In the case of a triggered aftershock sequence, it is very unlikely that the structure is repaired back to its intact condition during early phases of an ongoing sequence. Therefore, considering the (magnifying) effect of cumulative damage due to the triggered aftershock sequence in long-term seismic risk profile is not a trivial task. One viable strategy is to evaluate the increase in the (time-invariant) limit state excursion proba-bility due to the combined effect of short-term aftershock clustering and the resulting cumula-tive damage for a prescribed post-event short-term time interval. As expected, in case the structure is assumed to be renewed to a given hypothetic damage state (such as main-shock damaged) after each event occurs, the formulation for limit state probability simplifies to a closed-form Poissonian formulation. The methodology is applied to an existing 3-story RC moment-resisting frame in central Italy. The Poissonian closed-form solution, with the hy-pothesis of renewal back to the main-shock damaged configuration, is shown to successfully capture the increase in the limit state probability due to the effect of the triggered sequence.