1,721,005 research outputs found
Active deformation in the frontal part of the Northern Apennines: insights from the lower Metauro River basin area (northern Marche, Italy) and adjacent Adriatic off-shore
No full textAn integration of seismological data with geological and geomorphological information aided by seismic interpretation was performed to characterise the Quaternary tectonic evolution of the Metauro River basin area (northern Marche) and adjacent off-shore sector of the external Northern Apennines. On-shore, along the Adriatic coast, the youngest age of thrusting and folding post-dates the Early-Middle Pliocene, while Pleistocene deposits appear to be, at least in part, not involved in the deformation. Recent (i.e. post-thrusting) tectonic structures have been recognised both in pre-Quaternary substratum rocks and in Upper Quaternary continental deposits (Upper Pleistocene terrace alluvium, Upper Pleistocene-Holocene slope deposits). These faults are all compatible with a WSW-ENE oriented extension. In the Metauro River basin area, preserved flights of stream terraces have been categorised according to the presence or absence of alluvial suites in relationship to each terrace level. Here, based on both the heights above the valley floor and the areal distribution of stream terraces, a generalised vertical tectonic uplift can be inferred, particularly during the Middle-Late Pleistocene. Moreover, the along-valley distribution of stream terraces provides further constraints on the age of thrusting and folding. In fact, the reconstructed terrace-levels are substantially parallel, and no evidence for any significant deformation by fold activity has been recognised. Local deformation displayed by both terrace surfaces and alluvial/ slope-waste deposits suggests, instead, the intervening of some minor differential movements associated with the generalised uplift and/or to Middle-Late Pleistocene normal faulting. Their occurrence appears anyhow to be unrelated with the pattern of folds and associated thrusts. The present-day seismic activity of the study area was considered by analysing 83 seismic events that occurred from 1987 to 2000. The epicentre distribution is very scattered, and depths are generally comprised within the first 20 km of the crust, clustering between 0 and 15 km. Most of the events have magnitude < 3.0, while only a few of them (12) have magnitude between 3.0 and 4.2. Focal mechanisms were obtained for eight events. The results are complex, showing fault plane solutions of "normal fault", "thrust fault" and "unknown" types, according to commonly used stress categories. The low level of seismicity and the inhomogeneity of fault plane solutions confirm that, in the study area, this kind of data cannot provide clear constraints with respect to the problem of the occurrence or lack of activity along the thrust front. Finally, the Quaternary marine succession was studied in the northern Adriatic off-shore. Lower Pleistocene deposits appear to be slightly involved in the deformation associated with the frontal thrust of the Apennine chain. In contrast, the upper part of the Quaternary succession is clearly undeformed, showing planar and horizontal reflectors, which seal the most external thrusts of the belt. These data suggest that thrusting at the front of the Northern Apennines ended in Early Pleistocene times. Our integrated results indicate that, since Middle Pleistocene times, the external front of the northern Marche Apennines has been inactive. A generalised uplift has taken place, with subordinate tectonic activity being characterised by ENE-WSW extension and NNW-SSE compression. These main features of the stress field, although with spatial permutations of the principal stress axes, also characterise most of the external Northern Apennines during the whole Middle Pleistocene-Holocene time span
Land subsidence and active tectonics of a foreland area from SBAS-DINSAR technique (Hyblean plateau, Central Mediterranean)
No full textModes of fault reactivation from analogue modeling experiments: implications for the seismotectonics of the southern Adriatic foreland (Italy)
No full textThe active tectonics at the front of the Southern Apennines and in the Adriatic foreland is characterized by E–W striking, right-lateral seismogenic faults, interpreted as reactivated inherited discontinuities. The best studied among these is the Molise-Gondola shear zone (MGsz). The interaction of these shear zones with the Apennines chain is not yet clear. To address this open question, we developed a set of scaled analogue experiments, aimed at analyzing: (1) how dextral strike–slip motion along a pre-existing zone of weakness within the foreland propagates toward the surface and affects the orogenic wedge; (2) the propagation of deformation as a function of increasing displacement; (3) any insights on the active tectonics of Southern Italy. Our results stress the primary role played by these inherited structures when reactivated, and confirm that regional E–W dextral shear zones are a plausible way of explaining the seismotectonic setting of the external areas of the Southern Apennine
Reconciling large seismogenic sorce and shallow normal faults in the Messina straits: the analogue modelling perspective.
No full textRecent and present day kinematics along the triangle zone between Southern Alps and Emilian arc (Northern Apennines)
No full textShear zones from analogue modeling: insights on active regional strike-slip faults in Southern Apennines and Adriatic foreland
No full textNorthern Apennines and Southern Alps, two chains for the same foreland: recent kinematics and possible interactions
No full textThe kinematics of a fold-and-thrust belt or of parts of it can be influenced and modified by different factors, most of which have been thoroughly studied through years (syn-tectonic sedimentation, erosion, inherited structures, etc). Very few is known, however, on the possible influence that one thrust belt (or a single thrust) could exert on another one opposite verging. In the world, different cases of opposite verging thrust belts and shared foreland basins can be found (Rioja Through, Northern Spain; Middle Magdalena Valley, Colombia; Sevier fold-thrust-belt and Laramide foreland, North America, and others). An interesting case, characterized by a close distance between the outermost fronts of the two opposite verging orogenic fronts is represented by the Central Po Plain, in Italy. We investigated the propagation of the Northern Apennines on its foreland (Central Po Plain), in a sector where its outermost thrusts, buried under the Po Plain siliciclastic deposits, are close to those of an opposite verging chain, i.e., the Southern Alps. A regional cross-section, representative of this particular tectonic setting, has been restored in order to reconstruct the recent (post-Messinian) kinematics of the Apennines thrust fronts. An out-of-sequence propagation of the thrust faults was identified and its possible causes have been studied through analogue models. We reproduced in a sand-box the structural setting of the Central Po Plain, modeling the two opposite verging chains (Northern Apennines and Southern Alps). The experiment was set up to analyze the effects of an existing chain (Southern Alps) on an opposite verging one, which is developing toward the same foreland (Northern Apennines) while syntectonic deposits were sedimenting. The comparison between what observed through seismic lines and well logs and what shown by the models highlights that the presence of the Southern Alps fronts inhibits the propagation of the Northern Apennines fronts, leading to an out-of-sequence reactivation of the inner thrust fronts of the latter thrust belt. Comparison among the study area and its surroundings, along with a detailed analysis of the analogue models, revealed that syntectonic sedimentation cannot be the only factor responsible for the out-of-sequence reactivation of Northern Apennines inner fronts. Moreover, the presence of the Southern Alps buried fronts affects the Northern Apennines kinematics also when the two fronts are still far from colliding. The implications of this complex kinematics allow outlining some insights on the current seismotectonic setting of the area and on the possible evolution of this type of structures
Reconciling deep seismogenic and shallow active faults through analogue modeling: the case of the Messina Straits (Southern Italy)
No full textThe catastrophic 28 December 1908, Mw 7.1, Messina Straits earthquake was generated by a large, low-angle, SE-dipping, blind normal fault. A number of shallow, high-angle normal faults arranged in a graben-like fashion occur in the same area both on land and offshore, reaching the surface and in some instances affecting recent deposits. These faults are normally interpreted as active and have often been considered potentially seismogenic. We used an analogue modelling approach to simulate the evolution of a large, low-angle normal fault and investigate its relationships with the overlying secondary faults. We find that these faults represent the brittle surface expression of the long-term activity of the underlying master fault, and that all faults mapped by previous workers in the Messina Straits are compatible with sustained slip along the fault responsible for the 1908 earthquake. Our results confirm that analogue modelling provides a useful tool to investigate the evolution and the hierarchical relationships of fault systems, suggesting that this approach is effective in the investigation of complex seismogenic areas
The investigation of seismogenic sources through analogue modeling: insights from the 2009 L'Aquila earthquake (Mw 6.3, Italy)
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