Seismic hazard maps are predominately based on the classical methodology of probabilistic seismic hazard assessment, (PSHA). These maps are used to facilitate the safe design of buildings and infrastructure. However, in the literature there is extensive criticism of the use of PSHA for seismic hazard assessment. PSHA based maps have been widely perceived as having significantly underestimated several devastating earthquakes, over the last two decades, i.e. Wenchuan, China (2008), Haiti, (2010) and Tohoku – Oki, Japan, (2011). This dissertation investigates ‘why?’ and ‘how?’ this situation has come about, with the overarching aim of how to improve upon the current practice of seismic hazard assessment, (SHA).

Through a literature review, the primary cause of all the earthquakes investigated in this work, was found to be due to multi-segment, fault ruptures. To understand the theoretical and practical implications of such failures for SHA, an original, conceptual framework of an energy- based system of systems, was developed.

This conceptual framework was then used to support two new methodologies for SHA, at source and at specific sites, respectively. The first methodology (a) provides a time-dependent, deterministic seismic hazard assessment, for complex fault systems (TD-DSHA-CFS), and the second, (b) provides a ground response assessment, based on the combined use of ambient vibration, geophysical techniques in the field, soils laboratory testing and calibrated, numerical simulations, (1-D EQL).

The application and practical relevance of these methodologies is exemplified through a Case Study consisting of three sections, covering a complete SHA, for a given geographical region and a specific site. Case Study (A) applies the TD-DSHA-CFS to determine the maximum credible earthquake and recurrence interval for the Al-Idrissi Fault System (AIFS) in the Alboran Sea. The AIFS is a complex, multi-segment fault system, not considered in the current PSHA based seismic hazard maps for the region. Case Study (B), leverages the results of Case Study (A) to estimate the seismic peak ground acceleration (PGA) for several coastal cities on the SE Iberian and Moroccan coastlines, using TD-DSHA-CFS. The results show that the TD DSHA-CFS leads to significantly higher values of seismic hazard (Mw) at source and at one coastal city site (Melilla), in terms of PGA, in comparison with official PSHA map values.

The second methodology is applied for ground response assessment for a specific site in Gibraltar. The results show that the previous BS EN 1998-1(2004) and the recent update (2024), significantly underestimate the amplification values, used to determine seismic hazard at ground level. The results suggest that for highly heterogenous soil sites, ground response analysis, with the careful selection of modulus reduction and damping curves, may be in many instances more accurate than the methodology given in the new BS EN 1998-1 (2024).

Overall, these novel methodologies contribute to PSHA by comparing predicated ground motions, in order to evaluate the consistency and accuracy of the ESHM20 probabilistic model for the geographical area considered in the Case Study, herein.