Code-conformance assessment of seismic design spectra using validated web-based PSHA platforms: HazQuake & SearchQuake

Design spectra in seismic codes standardize structural responses to expected ground motions derived from seismic hazard analysis, ensuring safety and resilience. However, these spectra are regionally defined and may not accurately reflect the influences of site-specific conditions on earthquake ground motions. To ensure the safety and cost-effectiveness of critical structures, more accurate modeling of earthquake ground motions with detailed seismic hazard analysis (SHA) is often necessary. SHA enhances reliability by incorporating local site conditions, updated earthquake catalogs, and fault models. This study aims to evaluate the adequacy of the IR-2800 design spectrum for Tehran, Iran, a metropolis of immense geographic expanse and a dense population of millions, which amplifies the potential consequences of inadequate seismic design. To assess the adequacy of the IR-2800 design spectrum, a comparative analysis is conducted with PSHA-derived site-specific spectra at three locations. One location is situated within the city center, representing a far-fault site, while the other two locations positioned in the northern region of the city, constituting a near-fault site. Furthermore, the present study endeavors to address the challenges confronting design engineers in adopting contemporary SHA software. To this end, two online, platform-independent, location-based applications, SearchQuake and HazQuake, have been developed. These applications have been designed to improve numerical precision, reduce analysis time, and enhance usability through cloud computing. The results indicate that while the far-fault site exhibits lower seismic demand, the near-fault sites show significantly higher hazard, suggesting the need for revised design strategies or additional safety margins.