Seismic Hazard Assessment Research Articles

In-situ search for the origin of seismic repeaters in a deep mine, using geological and geomechanical measurements

Repeaters are repetitive seismic events with highly similar waveforms. They have been studied for decades by seismologists in natural environments and are commonly associated with the occurrence of aseismic slip (i.e. creep), loading seismogenic asperities on fault planes. Recently, long lasting repeater sequence (days to years) have been also observed in the active Garpenberg underground mine, Sweden. The presence of these phenomena may indicate that aseismic deformation induced by mining plays a role in triggering mine seismicity and thus has to be considered in seismic hazard assessment. To better understand the origin of these repeaters, we target one of the permanent repeater source located in the (∼25 m thick) horizontal sill pillar at 1 km depth using drilling cores and installation of strain cells in boreholes. By this in-situ investigation, we aim at observing structures and mechanisms responsible for the occurrence of repeaters, combining geological, geomechanical and geophysical observation. A clear co-seismic strain (∼6μɛ) during the occurrence of one repeater event enabled us to constrain the location of that source asperity, outside the area reached by the drillings. We show that the presence of an aseismic fault plane with at least one seismogenic asperity is consistent with field observations and that the drillings have probably crossed the aseismic portion of the fault plane. Finally, we discuss limitations of our installation, even if local and unique, to clearly identify the source mechanism behind the observed seismicity.

Findings from a decade of ground motion simulation validation research and a path forward

Simulated ground motions have the potential to advance seismic hazard assessments and structural response analyses, particularly for conditions with limited recorded ground motions such as large magnitude earthquakes at short source-to-site distances. However, rigorous validation of simulated ground motions is needed for hazard analysts, practicing engineers, or regulatory bodies to be confident in their use. A decade ago, validation exercises were mainly limited to comparisons of simulated-to-observed waveforms and median values of spectral accelerations for selected earthquakes. The Southern California Earthquake Center (SCEC) Ground Motion Simulation Validation (GMSV) group was formed to increase coordination between simulation modelers and research engineers with the aim of devising and applying more effective methods for simulation validation. Here, we summarize what has been learned in over a decade of GMSV activities, principally reflecting the views of the SCEC research community but also extending our findings and suggestions for a path forward to broader United States and worldwide simulation validation efforts. We categorize different validation methods according to their approach and the metrics considered. Two general approaches are to compare validation metrics from simulations to those from historical records or to those from semi-empirical models. Validation metrics are categorized into ground motion characteristics and structural responses. We discuss example validation studies that have been impactful in the past decade and suggest future research directions. Key lessons learned are that validation is application-specific, our outreach and dissemination need improvement, and much validation-related research remains unexplored.

Present-day crustal movement and seismic moment balance on major active faults around the easternmost segment of the Kunlun fault, Tibetan Plateau, China

After the 2021 Ms 7.4 Madoi, China earthquake located south of the eastern Kunlun fault, the coseismic Coulomb stress changes show that the earthquake potential is enhanced towards the easternmost segment of the Kunlun fault. Before the 2008 Mw 7.9 Wenchuan, China earthquake, the easternmost segment of the Kunlun fault is considered to being a region with the highest frequency occurrence of moderate-to-strong earthquakes in mainland China, where there are still at least three seismic gaps at present, indicating an urgent earthquake hazard. The tectonic deformation pattern is closely related to the development and occurrence of earthquakes. In this study, we collect all the available GPS data to obtain a crustal movement velocity field with high precision and high resolution by removing nontectonic effects within the study area. The GPS velocity profile and two-dimensional strain rates are then derived from the updated GPS velocities to analysis the characteristics of crustal deformation. Our results demonstrate that the Longriba fault zone slips predominantly right-laterally with the rate of 5.2 ± 0.5 mm/yr and the crustal shortening rate is ∼0.5 mm/yr across the Longriba and Longmenshan faults. Along with notable crustal extension and contraction, the principal strain rate field is distributed in a wide area on the northwest part of the Longmenshan fault, and decreases southwestward along the Longmenshan fault zone. In addition, we provide the time series of 8 campaign GPS stations which have never been published before. Moreover, the moment deficit estimate is a well-established way of assessing the earthquake hazard at a specific fault. Accompanying with the inverted slip rates and locking depth, we estimate the rates of moment accumulation on major faults and compare them with the seismic moment released on each fault derived from the Chinese historical earthquake catalog which extends for more than 2000 years in many regions. We find that the moment deficit is mainly concentrated on the Longriba fault with a value of 4.18 × 1017 Nm/yr. The Longriba fault have accumulated enough seismic energy to generate one Mw > 7.7 earthquake on it, or two Mw > 7.5 earthquakes on its two branches in the future. This study is an essential indicator for understanding the present-day tectonic deformation pattern in the Tibetan Plateau and is also helpful for seismic hazard assessment.

Identification of Source Faults of Large Earthquakes in the Turkey‐Syria Border Region Between 1000 CE and the Present, and Their Relevance for the 2023 Mw 7.8 Pazarcık Earthquake

AbstractThe 6 February 2023, Mw 7.8 Pazarcık earthquake in the Turkey‐Syria border region raises the question of whether such a large earthquake could have been foreseen, as well as what is the maximum possible magnitude (Mmax) of earthquakes on the East Anatolian Fault (EAF) system and on continental transform faults in general. To answer such questions, knowledge of past earthquakes and of their causative faults is necessary. Here, we integrate data from historical seismology, paleoseismology, archeoseismology, and remote sensing to identify the likely source faults of fourteen Mw ≥ 7 earthquakes between 1000 CE and the present in the region. We find that the 2023 Pazarcık earthquake could have been foreseen in terms of location (the EAF) and timing (an earthquake along this fault was if anything overdue), but not magnitude. We hypothesize that the maximum earthquake magnitude for the EAF is in fact 8.2, that is, a single end‐to‐end rupture of the entire fault, and that the 2023 Pazarcık earthquake did not reach Mmax by a fortuitous combination of circumstances. We conclude that such unusually large events are hard to model in terms of recurrence intervals, and that seismic hazard assessment along continental transforms cannot be done on individual fault systems but must include neighboring systems as well, because they are not kinematically independent at any time scale.

Application of Horizontal-to-vertical Spectral Ratio with a Dense Linear Array on Prospecting Urban Underground Active Faults: a Case in The Mingguang City, Anhui Province

Reliable knowledge of sedimentary structures is beneficial for the study of active faults covered by sediments and can also provide important information for seismic hazard assessment, earthquake emergency response and urban planning. Based on the dense seismic array with a spacing of ∼ 60 m between stations and a length of ∼ 8 km, the horizontal-to-vertical spectral ratio (HVSR) curves were obtained at 133 stations with the ambient noise, and the two-dimensional sedimentary structures of the Quaternary and Neogene strata were imaged over two main faults of the Tanlu fault zone in the eastern Jiashan Basin by frequency-depth conversion. The variations (∼ 130 m) in the depth of the Quaternary and Neogene sedimentary basement directly beneath the fault zone agree well with the spatial characteristics of the fault revealed by the shallow seismic reflection profile with active sources at the same locations.

Reconstructing Late Quaternary Paleovalley Systems of Italy Through mHVSR: A Tool for Seismic Hazard Assessment in Modern Coastal Lowlands

AbstractEffective site characterization in highly urbanized coastal lowlands requires accurate stratigraphic and geophysical investigations. In these regions, which typically host shallowly buried paleovalley systems formed in response to Quaternary glacio‐eustatic fluctuations, the marked lithologic contrast between soft sediment paleovalley fills and the adjacent, stiff substrate has the potential to modify earthquake motions, and assessment of critical parameters, such as shear wave velocities (VS) and resonance frequencies (f), should be coupled with detailed stratigraphic architecture. To evaluate the potential of the microtremor horizontal‐to‐vertical spectral ratio (mHVSR) for paleovalley recognition and mapping, we performed mHVSR measurements along the Adriatic coastal plain of Italy, where two paleovalley systems (Pescara and Manfredonia) have been recently identified. In both areas, we detected rapid lateral variations in resonance frequencies and highlighted laterally continuous impedance contrasts. Relying on a robust stratigraphic framework, we carefully evaluated the relation between geological and geophysical data and identified the stratigraphic surfaces responsible for the observed resonances. We derived VS models for the sediment fill, reconstructing the geometry of the two buried paleovalleys. We address the importance of evaluating the geological context when designing microzonation studies, for a reliable interpretation of changes in resonance frequencies.

Analysis of Crustal Movements in the Angren-Almalyk Mining Industrial Area Using GNSS Data

This study aims to investigate the potential of GNSS data in earthquake zoning and risk assessment in a seismically active region. The study area is located in Uzbekistan, where the interaction of several tectonic plates results in frequent earthquakes. The study focused on two periods from October to October of the next year, respectively, for 2018 and 2019, 2019 and 2020 to analyze GNSS velocities and earthquake zoning maps to identify areas at high risk of seismic activity. The study also utilized GIS and spline interpolation to create continuous surface maps of risk zones based on earthquake hazard data. The results showed that the entire study area is at high seismic risk, with a tendency for rotational movement in the zone of intersection of tectonic plates. Velocities range from 1.56-20.3 mm/yr and 1.64-14 mm/yr for the two periods. Moreover, the analysis of vertical earth surface displacements indicates a tendency towards soil subsidence in the western part and uplift in the northeastern part of the study area. The study concludes that GNSS analysis can provide valuable insights into seismic hazard assessment and improve our understanding of the tectonic processes leading to earthquakes.

Present-day crustal deformation based on GPS measurements in southeastern Tibetan Plateau: implications for geodynamics and earthquake hazard

GPS-derived strain rates can provide a tight constraint in understanding tectonic evolution of the Tibetan Plateau and are helpful in seismic hazard assessment. For this purpose, we at first verify the method, proposed by Zhu et al. in 2005 and 2006, for the computation of the strain rates, and found that the approach is reasonable and accurate. Then, based on the updated GPS data, we compute strain rates in southeastern Tibetan Plateau (SETP). The computed results showed that the strain rates in the Sichuan Basin and South China Block are very small, and the high values are largely concentrated along the Sagaing Fault and Xianshuihe-Anninghe-Xiaojiang fault system. In addition, the highest principal strain rates are located around the eastern Himalayan syntaxis (EHS), with the compressive orientations perpendicular to the Main Thrust Belt. In particular, the calculated extensive deformation basically matches the normal faulting earthquakes. In general, the characteristic of the strain rate distribution is in good agreement with the tectonic structures from the geological and geophysical investigations. At last, according to the strain rates, seismicity, and tectonic structures, we estimate five most likely zones for future major earthquakes in SETP. These areas include the Zemuhe Fault, northwestern segment of the Red River Fault, and at the intersection between the Ganzi-Yushu Fault and the Xianshuihe Fault, and at the one between the Zhongdian Fault and Jinshajiang Fault. Consequently, this study is significant in deep understanding of the geodynamics in the Tibetan Plateau and earthquake hazard assessment.

Complex fault system revealed by 3-D seismic reflection data with deep learning and fault network analysis

Abstract. Understanding where normal faults are located is critical for an accurate assessment of seismic hazard; the successful exploration for, and production of, natural (including low-carbon) resources; and the safe subsurface storage of CO2. Our current knowledge of normal fault systems is largely derived from seismic reflection data imaging, intracontinental rifts and continental margins. However, exploitation of these data sets is limited by interpretation biases, data coverage and resolution, restricting our understanding of fault systems. Applying supervised deep learning to one of the largest offshore 3-D seismic reflection data sets from the northern North Sea allows us to image the complexity of the rift-related fault system. The derived fault score volume allows us to extract almost 8000 individual normal faults of different geometries, which together form an intricate network characterised by a multitude of splays, junctions and intersections. Combining tools from deep learning, computer vision and network analysis allows us to map and analyse the fault system in great detail and in a fraction of the time required by conventional seismic interpretation methods. As such, this study shows how we can efficiently identify and analyse fault systems in increasingly large 3-D seismic data sets.

Assessment of the seismic hazard in North China by combining micro-seismicity records and geodetic observations

North China has suffered numerous devastating historical and recent earthquakes, causing huge loss of life and property. Therefore, it is vital to identify the regions with the greatest potential to generate large earthquakes in the future. Previous studies mainly evaluated the seismic hazard in North China using earthquake records or geodetic methods separately. Here, we evaluated the seismic records and geodetic observations in combination to comprehensively assess the earthquake potential. We first evaluated the earthquake catalog and determined that the completeness range of magnitude is 1.9 to 2.8 based on the b-values estimated by magnitude-frequency distribution using catalogs with different minimum-magnitude cutoffs. We then obtained the spatial distributions of three strain rate parameters, including the maximum shear, the principal, and second invariant of the strain rates, using interseismic Global Navigation Satellite System (GNSS) observations. The robustness of the strain rate model was validated by comparing previous studies. We then analyzed the seismic hazard in North China based on the strain rates and b-values and determined the regions with relatively high seismic hazard potentials. The results suggested that large strain rates are mainly concentrated on the western border of the Ordos Block and the Tangshan fault zone. Different strain rate parameters yielded similar spatial distributions of recurrence intervals with different magnitudes. We further revealed that the western border of the Ordos Block and Tangshan fault regions exhibit relatively short (∼7000–15,000 year) ML 7.5 earthquake recurrence times, compared with those of other regions in North China. Although the results obtained in this study were limited by the completeness of earthquake records, the spatial distribution of the GNSS observation, the assumption of elastic strain accumulation, and the complexity of the mechanisms of intraplate earthquakes, our findings will contribute to the assessment of seismic hazards in North China.

The Difficult Balance among Scientific, Technical, and Political Issues in Seismic Hazard Assessment

The Difficult Balance among Scientific, Technical, and Political Issues in Seismic Hazard Assessment

Ambient noise tomography of the Aegean region of Türkiye from Rayleigh wave group velocity

We have studied Rayleigh wave group velocities beneath the Aegean region of Türkiye using ambient noise tomography. Noise data were gathered from 43 broadband seismic stations belonging to three permanent broad-band arrays. The cross-correlation method was used to estimate empirical Green’s functions. Group velocities of the fundamental mode Rayleigh waves were determined using multiple filter technique. We measured dispersion for each station pair in a period range of 2–12 s and computed maps of group velocity distribution using the fast marching surface tomography method. The group velocity maps correlate well with the geological and tectonic features of the region, displaying low velocities for the Quaternary alluvial basins, moderate velocities for Cretaceous rocks, and high velocities for the regions where gneiss and granitoid rocks outcrop. Low velocity anomalies may be associated with the grabens and horsts formed by faulting and to deep mantle flow. We detect potential offshore geothermal zones in Izmir and Candarli Bay. The information from broad-band networks improves the resolution of crustal surface wave velocity structures, particularly for shallow depths. This improvement will support the assessment of seismic hazard, as the shallow layers of the crust contribute significantly to seismic activity.

Geophysical Processes in the Arctic and the System Analysis of their Impact on Operation and Development of the Transport Infrastructure

The scientific research that has become the subject of consideration in this article is related to assessment of the influence of geophysical factors on sustainable functioning of transport systems and the system analysis of their impact on the transport infrastructure at the Arctic latitudes. The research is a new direction in the field of study of operational reliability of transport systems and scientific support for development of transport infrastructure in the Russian Arctic.The paper touches upon the issues of reliability and possible failures of technical equipment under the influence of space weather, and also discusses multifaceted problems of safety and efficiency of development of transport systems considering new data on the structure and properties of the lithosphere referring to thawing of permafrost and mineral deposits. A separate section is devoted to new information on seismic activity and seismic hazard assessment in areas of operation and promising development of the transport infrastructure of the Arctic zone of the Russian Federation (AZRF).Intellectual accounting and generalisation of the obtained interdisciplinary results together with their visualisation are provided by geoinformatics methods. The paper presents also the results of adoption of modern geodatabase management systems, of the application of modern technologies of geoportals and interactive spherical visualisations for qualitative presentation of new geophysical knowledge obtained in the course of research.

Long-period directivity pulses of strong ground motion during the 2023 Mw7.8 Kahramanmaraş earthquake

Damages due to large earthquakes are influenced by broadband source effects that remain enigmatic. Here we develop a broadband (0–10 Hz) source model of the disastrous 2023 Mw7.8 Kahramanmaraş, Türkiye, earthquake by modeling recordings of 100 stations. The model combines coherent and incoherent rupture propagation at low and high frequencies, respectively. We adopt a planar 300 km long kinked fault geometry from geology and pre-constrain the slip model from seismic and geodetic data. We demonstrate that the southwestward rupture propagation was delayed by ~15 s and that the observed strong waveform pulses can be explained by the directivity effect due to a specific combination of the coherent and incoherent components. We show that even a rough estimate of major rupture parameters makes the ground motion simulations of such large events possible, and may thus improve the efficiency of rapid, physics-based, shaking estimation for emergency response and seismic hazard assessment.

Source characteristics of earthquakes in Delhi and its vicinity: Implications for seismogenesis in the stable continental region of India

Delhi and its surrounding region are among the important intraplate seismically active regions of India. According to the Bureau of Indian Standards, it lies in seismic zone IV and is capable of generating small to moderate earthquakes. This region has also experienced moderate to large earthquakes in the past due to its proximity to the Himalayan arc and its own tectonics. There is an urgent need to assess the source characteristics of earthquakes and their scaling relationships for a reliable and accurate estimation of seismic hazard. Source parameters and their scaling relations have been estimated for this region using well-located small to moderate earthquakes (Mw 2.3–5.1) that occurred during the period from 2000 to 2020. For this purpose, we investigated three components of earthquake waveform data using the ω−2 source model. The outcomes show the occurrence of low static stress drop (0.5–52.87 ​bars) in the Delhi region indicating approximately 57% of the events exhibit a stress drop < 10 ​bars, 27 % of events fall in the range of 10–20 ​bars, and only 16 % events exhibit stress drop > 20 ​bars. This observation suggests that the shallow subsurface of the study region may have low-strength material characteristics and a heterogeneous nature. In addition, the Zuniga parameter (ε) is estimated less than 1.0 by analyzing static and apparent stress drops, which infers the partial stress drop model fits very well in the study region. The seismic moment varies from 1.02×1012 to 1.03×1016 ​N.m. for P-wave and 6.46×1011 Nm to 7.54×1015 Nm for S-wave. The average seismic source radius lies in the range of 0.1–3.05 ​km with a ratio {r(p)/r(s)} of 1.5 ​km in the study region. The estimated values of corner frequency are comparatively lower for the S-wave (1.5–18.2 ​Hz) than for the P-wave (1.88–19.3 ​Hz) suggesting the ‘shifting properties’ of the corner frequency corroborated with the theoretical agreement. The seismic energy (E) is estimated using both P- and S-wave separately and its average value varies from 4.28×106 to 6.22×1011 ​J. The estimated stress drop and seismic moment demonstrate no correlation with each other. Therefore small to moderate-size earthquakes inherently follow the self-similarity behavior. The obtained scaling relationship between Seismic Moment and Corner Frequency is Mo=7.94∗1015fc−2.97. The derived scaling relations and source parameters are expected to provide a priori information for the assessment of seismic hazards and are useful in the simulation of strong ground motion characteristics in the region.

Co-seismic surface displacement of the June 21, 2022 MW6 Khōst, Afghanistan earthquake from InSAR observations

A robust estimation of the earthquake location, seismic moment, and fault geometry is essential for objective seismic hazard assessment. Seismic events in a remote location, specifically in the absence of seismic and GNSS networks, can be investigated effectively using the InSAR-based technique. This study adopts the Differential Interferometric SAR (DInSAR) technique to quantify the co-seismic surface displacement caused by the June 21, 2022, Khōst MW6 earthquake that occurred along the western plate boundary between the Indian and Eurasian plate. The interferograms show that the maximum surface deformation occurred on the northwest and southwest of the fault line. From coherence, the Line of Sight (LOS) displacement, and the co-seismic surface displacement analysis, it has been observed that surface deformation was most pronounced in the southwest region of the fault line, and the surface has moved to the opposite direction along the fault line, which indicates a sinistral slightly oblique strike-slip movement. This InSAR-based observation appears consistent with the seismic waveforms derived from co-seismic surface displacements. Further, it has been argued that the slip deficit accumulated during the period of the last about 48 years along the frontal region of the northward extension of the Suleiman range and associated fault zone is qualitatively estimated at about 1.5 m, which is consistent with the seismic waveforms derived finite slip model.

Comparison of earthquake catalogs for the Korean Peninsula declustered using three different methods

Earthquake catalogs include dependent earthquakes, which are spatiotemporally related, and independent or background earthquakes. In order to predict long-term seismicity or conduct a seismic hazard assessment, the dependent earthquakes must be removed to generate a declustered earthquake catalog. Several declustering methods have been proposed to date; however, the result of seismic hazard assessment may vary depending on which declustering methods are selected. In the present study, the catalog of earthquakes that were observed between 2016 and 2021 in and around the Korean Peninsula is declustered using the methods proposed by Gardner and Knopoff [1974], Reasenberg [1985], and Zhuang et al. [2002], and the resultant catalogs are compared. The seismicity parameters (a- and b-values) in the Gutenberg-Richter relationship are found to vary among the three declustered catalogs, thus affecting long-term earthquake predictions and seismic hazard assessment. The raw (original) and three declustered catalogs are also tested to see whether they follow the Poisson process. The minimum magnitude ( ) above which the null hypothesis of the Poisson process cannot be rejected in the earthquake catalogs ranges from 1.6 to 2.2, depending on the declustered catalog. Further, the obtained herein shows a large value compared to the completeness magnitude estimated in the present study. Comparing the curves representing the cumulative number of background earthquakes against the elapsed time for the declustered catalogs shows that the method by Zhuang et al. [2002] produces the result in the closest agreement with the real background seismicity curve.

Complex fault geometry controls dynamic rupture of the 2021 Mw7.4 Maduo earthquake, NE Tibetan Plateau

Geodetic observations and seismic inversions suggest that the 2021 Mw7.4 Maduo earthquake's rupture velocity differs in two directions. However, the dynamic mechanisms underlying these differences remain unclear. To address this issue, we constructed a three-dimensional finite element model implementing heterogeneous fault geometry and real topography and simulated the Maduo earthquake's dynamic rupture process, with the tectonic stress field varying with depth. The results show that the uneven distribution of normal and shear stresses on the fault plane, due to the complex geometry of the seismogenic fault, is the primary factor controlling rupture velocity and slips on the fault plane of the Maduo earthquake. The modelled results reproduced basic kinematic characteristics as indicated by the observation and inversion results of the Maduo earthquake. Our study also suggests that if an earthquake occurs in a region without significant changes in velocity structure and stress field distribution, the complex geometry of the seismogenic fault is responsible for the dynamic rupture process. These findings provide important insights into the rupture behaviour of geometrically complex faults and have important implications for seismic hazard assessments of these complicated fault systems.

Advances on the investigation of landslides by space-borne synthetic aperture radar interferometry

ABSTRACT Landslides are destructive geohazards to people and infrastructure, resulting in hundreds of deaths and billions of dollars of damage every year. Therefore, mapping the rate of deformation of such geohazards and understanding their mechanics is of paramount importance to mitigate the resulting impacts and properly manage the associated risks. In this paper, the main outcomes relevant to the joint European Space Agency (ESA) and the Chinese Ministry of Science and Technology (MOST) Dragon-5 initiative cooperation project ID 59,339 “Earth observation for seismic hazard assessment and landslide early warning system” are reported. The primary goals of the project are to further develop advanced SAR/InSAR and optical techniques to investigate seismic hazards and risks, detect potential landslides in wide regions, and demonstrate EO-based landslide early warning system over selected landslides. This work only focuses on the landslide hazard content of the project, and thus, in order to achieve these objectives, the following tasks were developed up to now: a) a procedure for phase unwrapping errors and tropospheric delay correction; b) an improvement of a cross-platform SAR offset tracking method for the retrieval of long-term ground displacements; c) the application of polarimetric SAR interferometry (PolInSAR) to increase the number and quality of monitoring points in landslide-prone areas; d) the semiautomatic mapping and preliminary classification of active displacement areas on wide regions; e) the modeling and identification of landslides in order to identify triggering factors or predict future displacements; and f) the application of an InSAR-based landslide early warning system on a selected site. The achieved results, which mainly focus on specific sensitive regions, provide essential assets for planning present and future scientific activities devoted to identifying, mapping, characterizing, monitoring and predicting landslides, as well as for the implementation of early warning systems.

Seismotectonic role of transversal structures in the Plio-Quaternary evolution of the external Marche Apennines (Italy)

We defined the seismotectonic setting of the external Marche Apennines (central Italy) by integrating geomorphological, structural and seismological data. The area is characterized by strong historical earthquakes, but the geometries and kinematics of the seismogenic sources have not previously been well defined. Plio-Quaternary Apennine compressional NW–SE structures are segmented by NE–SW-oriented transversal faults, the origin and role of which are still debated. We characterized the geometry, kinematics and activity of the four main transversal faults to better define their seismogenic potential. These high-angle, deeply rooted transversal fault systems have been mapped and separate the external Apennine sector into blocks and sub-blocks with different structural and evolutionary features. The integrated dataset showed that some inherited fault segments have recently been reactivated, displacing Quaternary deposits. The spatial distribution of seismicity indicates that some clusters of hypocentres are located within the basement. Stress field analysis using available focal mechanism solutions confirms the prevalence of left-lateral kinematics on roughly SW–NE-oriented structures. The transversal structures thus contribute to the longitudinal segmentation of the Apennine structures and, more generally, are involved in the northern part of the Adria plate kinematics towards the north and NNW. The assessment of seismic hazards and planning to mitigate risks in populated areas close to the Adriatic coast should consider these potentially active faults evidenced by instrumental seismicity and important historical earthquakes.