Special Issue: New Challenges in Seismic Hazard Assessment

1. Introduction

With the continuous development of society, the rapid urbanization of cities, and the increasing construction of large-scale infrastructure projects, seismic hazard studies are becoming increasingly necessary. Seismic hazard assessment faces challenges requiring advanced and comprehensive approaches to understand and mitigate potential risks. There are many studies on seismic hazard using different methodological approaches in Italy and worldwide. These include geological records, such as paleoearthquakes, paleotsunamis, and coseismic rupture models [1,2,3,4,5,6,7,8], macroseismic investigations for analyzing the damage evolution during seismic sequences [9,10,11,12,13], and geophysical studies, including seismic and electrical tomography, as well as gravity and magnetic imaging techniques [14,15,16,17].

This Special Issue focuses on recent advances in the study of seismic hazards from multiple perspectives. A key aspect of this issue is the contribution of new geological coseismic data and macroseismic analyses evaluated by the ESI scale [18]. These studies are particularly valuable for improving our understanding of the mechanisms of shallow faulting caused by small-to-medium earthquakes, even in volcano–tectonic settings. Currently, earthquake data in the magnitude range 3.0 < M < 5.0 are significantly lacking, making this research crucial to fill the current knowledge gap and improve the completeness of available seismic databases.

2. An Overview of Published Articles

This Special Issue contains eleven peer-reviewed articles, with different scientific approaches to evaluating seismic hazard. Below is a brief description of their contents.

Pischiutta M. et al. [Contribution 1] summarized the results of their studies regarding fault zones with different kinematics, where ground motion is polarized and amplified perpendicularly to the predominant fracture field due to stiffness anisotropy. The authors noted that, even at rock sites, seismic waves can undergo a “directional site resonance or amplification”, with greater motion along one site-specific azimuth on the horizontal plane. These effects are related to large-scale open cracks or microcracks in different geological environments and are characterized by maximum amplification transverse to the predominant fracture strike.

Silva P. et al. [Contribution 2] studied the application of lichenometric analyses to unravel the chronology of bedrock fault scarps, where other paleoseismological techniques commonly used in alluvial and colluvial materials are harsh. The work completed the preliminary lichenometry analysis of rocky fault scarps on Mallorca Island. The analysis identified recurrent displacements of the Sencelles fault scarp based on different lichen colonization ribbons. Part of the youngest basal ribbon was tentatively related to the 1851 CE Palma Earthquake (≤VIII EMS Intensity).

Observed displacements cannot be truly cataloged as surface faulting events, but as secondary or sympathetic coseismic ground ruptures.

Based on some fundamental assumptions and physical formulas, Li W. et al. [Contribution 3] simulated the process by which many positive and negative ions are generated by radioactive gases before an earthquake. The results suggest that, under ideal conditions, positive and negative ions can be separated due to the combined influence of gravity, atmospheric electrostatic force, thermal driving force, and air resistance. This separation could lead to a negative anomaly forming in the near-surface atmospheric electric field. The proposed model is one possibility for explaining the negative atmospheric electric field anomalies observed before earthquakes (EQs). Nevertheless, the physical processes before EQs, as well as the coupling relationships, require further in-depth study.

Huang Y. et al. [Contribution 4] observed magnetic anomalies and proposed an innovative algorithm to capture data for geomagnetic anomalies before earthquakes. The algorithm accumulates geomagnetic anomaly energy to eliminate external environmental interference and takes its gradient as a measure for predicting the occurrence time of an earthquake. The authors concluded that the geomagnetic anomalies caused by earthquakes can be observed before earthquakes with high probability and can be used for earthquake prediction.

Kim et al. [Contribution 5] studied shear-wave velocity structures in the volcanic region of Jeju Island by horizontal-to-vertical spectral ratios (HVSRs) of environmental noise using advanced algorithms and HVSR curve analysis. The authors identified significant low-velocity layers (LVLs) composed of quaternary marine sediments, crucial for site amplification and attenuation in the area for hazard assessment.

Sayed S. R. Moustafa et al. [Contribution 6] conducted a geostatistical analysis of 24,321 seismic events in the Red Sea region from 1997 to 2020, integrating both spatial and temporal dimensions of seismic data, to provide a comprehensive understanding of seismic patterns. They applied a suite of spatial analytic methods, including ANN, QCA, Global Moran’s I, Local Moran’s I, and the Getis–Ord Gi* statistic, to highlight spatial clusters of seismic activity. Their findings outline distinct seismic patterns along the Central Red Sea axis, which are indicative of the rifting dynamics between the African and Arabian plates.

Rodriguez-Pascua M. A. et al. [Contribution 7] studied the kinematics of active faults and the depth distribution of earthquakes during the Tajogaite eruption and identified two master faults that have been active since before the 2021 eruption: the Tazacorte Fault (TZF) and the Mazo Fault (MZF). These faults are noted for a creep movement producing deformations and structural damage in anthropogenic constructions. The authors showed that both faults are still moving aseismically following the 2021 eruption and could be future sources of earthquakes of low magnitude but high macroseismic intensity.

Manic and Bulajic [Contribution 8] critically reviewed and analyzed the historical data of the 8 April 1893 Svilajnac (Serbia) Earthquake. Their analysis accounted for a variety of sources, including books, scientific publications, reports, newspapers, and coeval chronicles. This allowed the authors to reassess the location, magnitude, and macroseismic intensity map of the earthquake.

Paoletti et al. [Contribution 9] conducted large-depth Ground-Penetrating Radar investigations of the seismogenic Casamicciola fault system on the volcanic island of Ischia, aiming to constrain the source characteristics of this active and capable fault system and contributing to the knowledge on the seismic hazard of the island. The data highlighted variations in the electromagnetic signal due to the presence of contacts, i.e., faults down to a depth larger than 100 m below the surface. These signal variations match the position of the synthetic and antithetic active fault system bordering the Casamicciola Holocene graben. This study highlights the importance of large-depth Ground-Penetrating Radar geophysical techniques for investigating active fault systems not only in their shallower parts, but also down to a few hundred meters’ depth.

Katona T.J. [Contribution 10] assessed the safety relevance of fault displacement hazard due to the fault beneath the plant that was presumably reactivated during the Late Pleistocene period. The improved engineering fault–displacement hazard evaluation method is related to the Paks nuclear power plant in Hungary. Engineering methods estimate the probability of rupture at the site crossing and consider the displacement distribution over the rupture length relative to the site’s on-fault location. The simplified methods proposed by the author can be managed in a short time with significant cost savings in the long term.

Lacour and Abrahamson [Contribution 11] utilized non-ergodic ground-motion models (GMMs) in probabilistic seismic hazard analysis for areal sources, applying their approach to Southern France. In order to reduce the computation time, the authors employ, for hazard calculations, a Polynomial Chaos (PC) expansion with a Taylor series approximation to capture the spatial correlation effects of the non-ergodic terms.

The articles collected in our Special Issue highlight progress in the study of seismic risk, with significant results in geological, geophysical, and engineering methodological approaches.