This study employs a multimethod approach to investigate the sediment distribution in two pocket beaches, Ramla Beach and Mellieha S Beach, in Malta. Both study sites were digitally reconstructed ...using unmanned aerial vehicle (UAV) photogrammetry. For each case, an ERT and a dense network of ambient seismic noise measurements processed through a horizontal-to-vertical spectral ratio (HVSR) technique were acquired. Electrical resistivity tomography (ERT) analysis enables the estimation of sediment thickness in each beach. HVSR analysis revealed peaks related to beach sediments overlying limestone rocks in both sites and also indicated a deeper stratigraphic contact in Mellieha S Beach. Based on ERT measurements, sediment thickness is calculated for each HVSR measurement. Interpolation of results allows for bedrock surface modelling in each case study, and when combined with digital terrain models (DTMs) derived from photogrammetric models, sediment volumes are estimated for each site. The geometry of this surface is analyzed from a geological perspective, showing structural control of sediment distribution due to a normal fault in Mellieha S Beach and stratigraphic control facilitated by a highly erodible surface in Ramla Beach. The results emphasize the importance of adopting a three-dimensional perspective in coastal studies for precise sediment volume characterization and a deeper understanding of pocket beach dynamics. This practical multimethod approach presented here offers valuable tools for future coastal research and effective coastal management, facilitating informed decision making amidst the growing vulnerability of coastal zones to climate change impacts.
We present the first high-quality catalog of early aftershocks of the three mainshocks of the 2016 central Italy Amatrice-Visso-Norcia normal faulting sequence. We located 10,574 manually picked ...aftershocks with a robust probabilistic, non-linear method achieving a significant improvement in the solution accuracy and magnitude completeness with respect to previous studies. Aftershock distribution and relocated mainshocks give insight into the complex architecture of major causative and subsidiary faults, thus providing crucial constraints on multi-segment rupture models. We document reactivation and kinematic inversion of a WNW-dipping listric structure, referable to the inherited Mts Sibillini Thrust (MST) that controlled segmentation of the causative normal faults. Spatial partitioning of aftershocks evidences that the MST lateral ramp had a dual control on rupture propagation, behaving as a barrier for the Amatrice and Visso mainshocks, and later as an asperity for the Norcia mainshock. We hypothesize that the Visso mainshock re-activated also the deep part of an optimally oriented preexisting thrust. Aftershock patterns reveal that the Amatrice Mw5.4 aftershock and the Norcia mainshock ruptured two distinct antithetic faults 3-4 km apart. Therefore, our results suggest to consider both the MST cross structure and the subsidiary antithetic fault in the finite-fault source modelling of the Norcia earthquake.
We report the results of a shallow electrical resistivity investigation performed across a normal fault that ruptured the surface displacing with average ~0.05m vertical offset alluvial fan deposits ...(<23kyr old) within an intermontane fault-bounded basin following the 30 October 2016 Mw 6.5 earthquake in central Italy. We adopted a multi-scale geophysical approach, by acquiring three 2-D electrical resistivity tomography (ERT) profiles centred on the coseismic ruptures, and characterized by different spatial resolution and investigation depth. Below the fault scarp, the ERT models show a narrow (~10m wide) and steeply-dipping moderately-resistive region (100–150Ωm), which we interpret as the electrical response of the fault zone displacing layers of relatively high-resistivity (300–700Ωm) values. We explain the electrical signature of the retrieved fault zone as due to an increment of permeability caused by coseismic fracturing, and to the subsequent water migration from adjacent shallow aquifers squeezed by compaction induced by seismic waves. By using a statistically-based classification of electrical units, we estimate that the shallowest alluvial fan layer is affected by 2.7±0.9m vertical offset, which is consistent with the measured 2.3–2.8m morphologic offset of the top fan surface, and suggesting a post-12 kyr throw-rate of 0.23±0.08mm/yr. Similarly, we evaluate a post-23 kyr throw of 5.1±1.7m, indicating a Late Pleistocene throw-rate of 0.22±0.07mm/yr, in accordance with available paleoseismic data. We further hypothesize a minimal total fault throw >30m, which likely accrued since the Middle Pleistocene (possibly in the last 350–500kyr). The investigated fault structure is therefore an important splay characterized by a thick and highly permeable damage zone in unconsolidated deposits, and which ruptured the surface during several tens of strong (M>6) earthquakes.
•The 2016 Mw6.5 earthquake (Italy) caused surface faulting in the Castelluccio plain.•Multi-scale electrical tomography reveals a conductive fault zone in alluvium.•We detected several electrical units using a statistically-based approach.•Incremental offset of deep units yields post-LGM throw-rates of 0.22±0.07mm/yr.•Coseismic aquifer compression promoted fluid migration into the fault zone.
We present a 1:10,000 scale map of the coseismic surface ruptures following the 26 December 2018 Mw 4.9 earthquake that struck the eastern flank of Mt. Etna volcano (southern Italy). Detailed rupture ...mapping is based on extensive field surveys in the epicentral region. Despite the small size of the event, we were able to document surface faulting for about 8 km along the trace of the NNW-trending active Fiandaca Fault, belonging to the Timpe tectonic system in the eastern flank of the volcano. The mapped ruptures are characterized in most cases by perceivable opening and by a dominant right-oblique sense of slip, with an average slip of about 0.09 m and a peak value of 0.35 m. It is also noteworthy that the ruptures vary significantly in their kinematic expression, denoting locally high degree of complexity of the surface faulting.
In the Eastern Alps, the indentation of the Adriatic promontory since the Cenozoic affected the kinematics of separate crustal domains bounded by faults that accommodate lateral extrusion processes ...and differential shortening. Deciphering the pattern of crustal stresses in the orogen interior is challenging, due to the lack of in situ stress measurements at crustal depths. We define stress regimes and the orientations of the most‐compressive horizontal stress (SHmax) by integrating published results with new data, including stress analysis from fault plane solutions, estimation of crustal anisotropy through the shear wave splitting analysis, paleostress determination from fault slip data, and computation of cumulative seismic displacements. The retrieved regional SHmax are generally consistent with N‐S convergence. In the northern part of the study area, current stress orientations are almost parallel to paleo‐SHmax, suggesting a rather uniform compressional regime since the late Cenozoic. Conversely, sharp deflections and divergence with paleo‐SHmax appear at the western border of the Adriatic promontory across major transpressive and extensional shear zones and in the Southalpine domain, indicating a change in tectonically induced second‐order stresses. A current strike‐slip regime with subordinate orogen‐parallel seismic displacements affects a belt to north of the Periadriatic Lineament and NE‐extension characterizes the Ortles‐Engandine region. Seismic anisotropy locally exhibits fault‐parallel fast axes (Brenner‐Giudicarie fault‐systems, Dinaric and Southalpine thrusts), whereas stress‐induced anisotropy parallel to SHmax characterizes the southern part of the orogen. Cumulative seismic displacements are small compared to geodetic ones, and unravel partitioning of deformation into second‐order transpressive and extensional belts in response to indentation.
Key Points
Stress patterns in the Eastern Alps from earthquakes, seismic anisotropy and fault slip data
Partitioning of second‐order stresses and seismic strain into crustal domains in response to collision and lateral extrusion
Crustal seismic anisotropy primarily controlled by active stresses, major faults and pervasive fabric in the basement
The footwall of the surface rupturing Paganica normal fault, the source of the 2009 L’Aquila earthquake (Mw 6.1) in the Central Apennines (Italy), was investigated using integrated geological and ...geomorphological approaches. The aim was to constrain the active tectonics by studying the Raiale River that orthogonally crosscuts the fault trace, where it provides a useful geomorphological marker of long-term fluvial incision and footwall uplift. Using morphostratigraphy and paleomagnetic analysis, the Plio–Pleistocene morphotectonic evolution of the area was reconstructed, comprising an ancient continental basin and paleolandforms that predate the footwall incision. Starting from the Late Early Pleistocene–Middle Pleistocene, fluvial dissection was mainly due to marked river downcutting triggered by significant activity of the Paganica Fault, which caused progressive base-level lowering. The Raiale River downcutting formed five Middle–Late Pleistocene fluvial terraces, that, along with absolute Optically Stimulated Luminescence (OSL) dating, allowed the identification of paleolongitudinal profiles with a diverging downstream configuration. Terrace dating yielded a minimum incision rate of 0.25 ± 0.02 mm/a, which only partially compensates the footwall uplift and can thus be considered as a minimum value for the Paganica Fault throw rate, which could reach up to ~0.45 mm/a. In parallel, using terrestrial cosmogenic nuclides, a denudation rate of 0.02–0.04 mm/a was measured on the summit of the footwall block. This denudation is in keeping with the drainage incision, suggesting a non-steady state for the fault footwall topography and a dominance of relief growth. Last, the analysis of the modern Raiale River longitudinal profile denoted an ungraded status, with two main knickzones that we interpret as transient forms due to tectonic perturbations, likely triggered by activity of the Paganica Fault during the end Early Pleistocene and the Late Pleistocene. Considering the 2009 L’Aquila earthquake coseismic rupture, we observe that the younger transience on the Raiale River longitudinal profile, if it is of tectonic origin, could have only been produced by much larger seismic events (i.e., Mw > 6.5) than those documented in the area by paleoseismological investigations. The collective results confirmed that in the Central Apennines, conditions of dynamic equilibrium are often not met, and that the persistence of transient perturbations induced by tectonics should be accounted for.
•The active Paganica Fault triggered the Raiale River incision of the footwall block.•Reconstruction of Quaternary evolution identified paleo-base levels of the river.•The fluvial terrace dating (paleo base level) yields an incision rate of 0.25 mm/a.•Estimated incision rates equal the footwall uplift and reach up to ~0.45 mm/a.•Denudation rate of 0.02–0.04 mm/a indicates non-steady-state of the footwall block.
We present the first seismic reflection images of the Paganica and Bazzano basins, two tectonic basins developed in the hanging wall of the Paganica‐San Demetrio Fault System, the causative fault of ...the 2009 Mw 6.1 L'Aquila earthquake, Italy. Five high‐resolution seismic profiles were acquired along a main, 7 km long transect cutting across the strands of an active fault system in urbanized areas with widespread sources of seismic noise. Three processing approaches were chosen to tackle a variable and site‐dependent data quality . To aid interpretation of this complex setting, we complemented seismic amplitude images with energy and similarity attributes as well with post‐stack acoustic impedance inversion. The final seismic sections expose, with unprecedented resolution, the basins' structure and the uppermost splays of the 2009 earthquake. The seismic data show fine details of the subsurface stratigraphic setting, revealing continental depocenters carved in the marine Meso‐Cenozoic substratum and displaced by a series of conjugate normal faults, mostly unknown before this study. Several of the imaged fault strands connect to the 2009 coseismic surface ruptures. Matching the seismic interpretation with constraints from surface geology and shallow boreholes, published data from field surveys and scientific drilling, we present a structural map of the Bazzano and Paganica basins with an estimation of the depth of the Meso‐Cenozoic substratum. This map highlights a different structure, evolution, and age of the two basins, with the older Bazzano basin that likely began to form in late Pliocene.
Key Points
Five high‐resolution seismic profiles image the shallow architecture of the 6 April 2009 (Mw 6.1) L'Aquila earthquake fault hanging wall
The final images expose the structure of Paganica and Bazzano basins and seismogenic faults dissecting them with unprecedented resolution
Interpretation of seismic data suggests that Paganica and Bazzano basins have different age, structure, and evolution
The island of Malta (central Mediterranean) is dissected by several WSW-trending fault-line valleys related to Miocene-Pliocene extensional tectonics. Some valleys host remnants of alluvial deposits ...that could provide information on possible Quaternary faulting, but the thickness of these deposits and their subsurface extent is poorly constrained. Our study aimed to investigate the structural configuration of the southern sector of the Mellieha valley, which is located in the north-west part of the island and is limited by the ENE-WSW general trending Mellieha and Ghadira faults, and their relation with a thin layer of infill sediments. We employed different near-surface geophysical techniques (electrical resistivity tomography, active and passive seismic methods, ground-penetrating radar), as well as remote sensing techniques (unmanned aerial vehicle digital photogrammetry and ground-based Light Detection and Ranging) to complement classic structural surveys. The valley structure has an asymmetric graben configuration, being bounded by a normal fault to the southeast (Mellieha Fault) and other to the north-west (Ghadira Fault). Our study provides insights of possible Quaternary fault displacements and revealed the presence of an additional fault splay, the previously unmapped NNW-dipping Mellieha Fault 2 at the south-eastern edge of the valley. Additionally, by integrating results from geophysical surveys, we estimated the thickness of the valley's recent deposits, being thicker towards the Mellieha Bay sector, with maximum values of 8–10 m. Our study aligns with the general model of horst and graben structuring with associated regional tilting since the late Miocene, and supports the hypothesis that some segments of NW-trending normal faults within the North Malta Graben exhibit Quaternary activity, although with minimal throw rates (<< 0.1 mm/yr).
•Geophysical methods unveil recent sediment thickness in horst-and-graben domain.•Integration of geophysics and digital outcrops reveals valley structure.•Bathymetric data is used to map offshore fault extensions.
On May 20, 2012, a Ml 5.9 seismic event hit the Emilia Po Plain, triggering intense earthquake activity along a broad area of the Po Plain across the provinces of Modena, Ferrara, Rovigo and Mantova ...(Figure 1). Nine days later, on May 29, 2012, a Ml 5.8 event occurred roughly 10 km to the SW of the first main shock. These events caused widespread damage and resulted in 26 victims. The aftershock area extended over more than 50 km and was elongated in the WNW-ESE direction, and it included five major aftershocks with 5.1 ≤Ml ≤5.3, and more than 2000 minor events (Figure 1). In general, the seismic sequence was confined to the upper 10 km of the crust. Minor seismicity with depths ranging from 10 km to 30 km extended towards the southern sector of the epicentral area (ISIDe, http://iside.rm.ingv.it/). …
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