Exploring Near-Fault Directivity Effect in Probabilistic Seismic Hazard Assessment

Abstract eng:
Near-fault directivity effects can produce ground motions with high-amplitude, short duration pulses, which may cause serious damage to structures and buildings. Their prediction has important implications in the design of earthquake resistant structures. Prompted by the NGA-West2 project, several directivity models that aim to provide a more accurate estimate of hazard values – possibly in a probabilistic framework - have been recently proposed. To model the near-fault directivity effect in a probabilistic seismic hazard analysis (PSHA) framework, it is necessary to account for the aleatory variability of the hypocentral location and slip angle (for certain models) on each rupture generated by each fault source at close distance from the investigated site. This is a modeling approach not regularly considered in the more conventional PSHA practice, since the location of the hypocenter is rarely used in modern ground motion prediction equations (GMPEs). We implemented into the OpenQuake-engine (an open software for seismic hazard and risk assessment) some of the most recently published directivity models and we extended the ordinary hazard integral by adding two additional aleatory variables, hypocenter location and slip angle, to support the near-fault directivity effect PSHA calculation. Using a sample scenario based on an eighty-kilometer strike-slip fault and fixing as a reference the hazard values computed without accounting for the directivity effect, we observe at some sites surrounding the fault an increase of the values of ground motion up to 65 % at both 2 % and 10% probability of exceedance in 50 years. The discrepancy indicates the importance of considering the near-fault effect into the analysis for near-fault sites. As many major urban areas worldwide, such as San Francisco and Istanbul, are exposed to hazard caused by large faults with short distances. In this contribution, we describe the outcomes of some sensitivity analyses on the hazard results based on various distribution of the hypocentral location and fault geometries. We find that the hypocenter location has a strong impact on the hazard results, especially for scenario calculation, and that an over-simplified fault geometry model produces results which should be consider carefully while performing near-fault directivity PSHA.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket