Seismic and geodetic moment-rate comparisons can reveal regions with unexpected potential seismic hazards. We performed such a comparison for the Southeastern Iberia—Maghreb region. Located at the western Mediterranean border along the Eurasia–Nubia plate convergence, the region has been subject to a number of large earthquakes (M ≥ 6.5) in the last millennium. To this end, on the basis of available geological, tectonic, and seismological data, we divided the study area into twenty-five seismogenic source zones. Many of these seismogenic source zones, comprising the Western Betics, the Western Rif mountains, and the High, Middle, and Saharan Atlas, are characterized by seismic/geodetic ratio values lower than 23%, evidencing their prevailing aseismic behavior. Intermediate seismic/geodetic ratio values (between 35% and 60%) have been observed for some zones belonging to the Eastern Betics, the central Rif, and the Middle Atlas, indicating how crustal seismicity accounts only for a moderate fraction of the total deformation-rate budget. High seismic/geodetic ratio values (> 95%) have been observed along the Tell Atlas, highlighting a fully seismic deformation.
The Adria microplate is the foreland of the oppositely verging Apennines and Alps or Dinarides fold‐thrust belts associated to the related subduction zones. Along its western margin, the Adria plate hosts the active Northern Apennines accretionary prism, which is buried under the Adriatic Sea and the Po Plain. The interpretation of seismic reflection profiles and borehole data allowed us to define the geometry of the transition from the Apennines fold‐thrust belt to its undeformed foreland. Moreover, continuous GPS (CGPS) data from offshore hydrocarbon platforms anchored to the seabed of the northern Adriatic plate allow to measure present‐day kinematics. Although the CGPS signals are affected by non‐tectonic components associated with hydrocarbon extraction, the integration of geodetic analysis, subsurface geological reconstructions, and analytical modeling allowed us to constrain the ongoing tectonic activity. Shortening is currently accommodated by aseismic slip along the basal detachment, likely accumulating elastic energy along the frontal ramp that may eventually seismically slip. Our multidisciplinary study suggests that the study area may not be sheltered from relevant seismic sequences similar to the Mw 6 Emilia 2012 events and that the occurrence of potential seismogenic sources in the area should be carefully evaluated. Similar studies may be useful to constrain the present‐day activity in other marine areas and to identify potential and hitherto unrecognized seismogenic sources along the entire Apennines belt and other accretionary prisms worldwide.
Based on multidisciplinary data, including seismological and geodetic observations, as well as seismic reflection profiles and gravity maps, we analysed the pattern of crustal deformation and active tectonics in the Sicily Channel, a key observation point to unravel the complex interaction between two major plates, Nubia and Eurasia, in the Mediterranean Sea. Our data highlight the presence of an active ~ 220-km-long complex lithospheric fault system (here named the Lampedusa-Sciacca Shear Zone), approximately oriented N–S, crossing the study area with left-lateral strike-slip deformations, active volcanism and high heat flow. We suggest that this shear zone represents the most active tectonic domain in the area, while the NW–SE elongated rifting pattern, considered the first order tectonic feature, appears currently inactive and sealed by undeformed recent (Lower Pleistocene?) deposits. Estimates of seismological and geodetic moment-rates, 6.58 × 1015Nm/year and 7.24 × 1017Nm/year, respectively, suggests that seismicity accounts only for ~ 0.9% of crustal deformation, while the anomalous thermal state and the low thickness of the crust would significantly inhibit frictional sliding in favour of creeping and aseismic deformation. We therefore conclude that a significant amount of the estimated crustal deformation-rate occurs aseismically, opening new scenarios for seismic risk assessments in the region.
The Himalaya–Tibet region represents a complex region of active deformation related to the ongoing India–Eurasia convergence process. To provide additional constraints on the active processes shaping this region, we used a comprehensive dataset of GNSS and focal mechanisms data and derived crustal strain and stress fields. The results allow the detection of features such as the arc-parallel extension along the Himalayan Arc and the coexistence of strike-slip and normal faulting across Tibet. We discuss our findings concerning the relevant geodynamic models proposed in the literature. While earlier studies largely emphasized the role of either compressional or extensional processes, our findings suggest a more complex interaction between them. In general, our study highlights the critical role of both surface and deep processes in shaping the geodynamic processes. The alignment between tectonic stress and strain rate patterns indicates that the crust is highly elastic and influenced by present-day tectonics. Stress and strain orientations show a clockwise rotation at 31°N, reflecting deep control by the underthrusted Indian Plate. South of this boundary, compression is driven by basal drag from the underthrusting Indian Plate, while northward, escape tectonics dominate, resulting in eastward movement of the Tibetan Plateau. Localized stretching along the Himalaya is likely driven by the oblique convergence resulting from the India–Eurasia collision generating a transtensional regime over the Main Himalayan Thrust. In Tibet, stress variations appear mainly related to changes in the vertical axis, driven by topographically induced stresses linked to the uniform elevation of the plateau. From a broader perspective, these findings improve the understanding of driving crustal forces in the Himalaya–Tibet region and provide insights into how large-scale geodynamics drives surface deformation. Additionally, they contribute to the ongoing debate regarding the applicability of the stress–strain comparison and offer a more comprehensive framework for future research in similar tectonic settings worldwide.
The comparison between crustal stress and surface strain azimuthal patterns has provided new insights into several complex tectonic settings worldwide. Here, we performed such a comparison for Egypt taking into account updated datasets of seismological and geodetic observations. In north-eastern Egypt, the stress field shows a fan-shaped azimuthal pattern with a WNW–ESE orientation on the Cairo region, which progressively rotated to NW–SE along the Gulf of Aqaba. The stress field shows a prevailing normal faulting regime, however, along the Sinai/Arabia plate boundary it coexists with a strike–slip faulting one (σ1 ≅ σ2 > σ3), while on the Gulf of Suez, it is characterized by crustal extension occurring on near-orthogonal directions (σ1 > σ2 ≅ σ3). On the Nile Delta, the maximum horizontal stress (SHmax) pattern shows scattered orientations, while on the Aswan region, it has a WNW–ESE strike with pure strike–slip features. The strain-rate field shows the largest values along the Red Sea and the Sinai/Arabia plate boundary. Crustal stretching (up to 40 nanostrain/yr) occurs on these areas with WSW–ENE and NE–SW orientations, while crustal contraction occurs on northern Nile Delta (10 nanostrain/yr) and offshore (~35 nanostrain/yr) with E–W and N–S orientations, respectively. The comparison between stress and strain orientations over the investigated area reveals that both patterns are near-parallel and driven by the same large-scale tectonic processes.
A comparative analysis of geodetic versus seismic moment-rate estimations makes it possible to distinguish between seismic and aseismic deformation, define the style of deformation, and also to reveal potential seismic gaps. This analysis has been performed for Egypt where the present-day tectonics and seismicity result from the long-lasting interaction between the Nubian, Eurasian, and Arabian plates. The data used comprises all available geological and tectonic information, an updated Poissonian earthquake catalog (2200 B.C.–2020 A.D.) including historical and instrumental datasets, a focal-mechanism solutions catalog (1951–2019), and crustal geodetic strains from Global Navigation Satellite System (GNSS) data. The studied region was divided into ten (EG-01 to EG-10) crustal seismic sources based mainly on seismicity, focal mechanisms, and geodetic strain characteristics. The delimited seismic sources cover the Gulf of Aqaba–Dead Sea Transform Fault system, the Gulf of Suez–Red Sea Rift, besides some potential seismic active regions along the Nile River and its delta. For each seismic source, the estimation of seismic and geodetic moment-rates has been performed. Although the obtained results cannot be considered to be definitive, among the delimited sources, four of them (EG-05, EG-06, EG-08, and EG-10) are characterized by low seismic-geodetic moment-rate ratios (60%) have been observed, reflecting a fully seismic deformation.