Near-Field PSHA with Directivity – Dorud

Abstract

This study investigates the probabilistic seismic hazard in Dorud city, located near the active Dorud fault, with a specific focus on incorporating near-field and rupture directivity effects into the hazard modeling framework. Near-field ground motions – particularly those influenced by rupture directivity – can generate long-period velocity pulses, posing serious risks to long-period structures such as bridges and tall buildings near faults. To realistically capture these effects, this study integrates empirical directivity models (Somerville et al., 1997; Abrahamson, 2000) into the probabilistic seismic hazard assessment (PSHA). The seismicity parameters were derived using the Kijko (2004) method based on a carefully declustered earthquake catalog; the suitability of this catalog for PSHA was statistically confirmed through a Kolmogorov‑Smirnov (K‑S) test, validating the Poissonian nature of inter-event times.Seismic hazard calculations were performed for vibration periods of 0.75, 1, 2, 3, and 4 seconds and return periods of 50, 475, and 2475 years. The study further includes deaggregation analysis to examine how near-field and directivity effects influence magnitude and distance contributions to hazard. The results show that the influence of directivity increases with both return period and vibration period. The most significant amplification – a 17.16% increase in acceleration – occurs when directivity is included for a 2475-year return period at a 4-second vibration period. A regional comparison of seismicity parameters with previous PSHA studies supports the robustness of the selected input values. This study demonstrates the importance of explicitly incorporating directivity in PSHA for fault-adjacent urban areas, especially for engineering design of critical long-period structures