1,721,032 research outputs found
Identification of seismogenic nodes in the Alps and Dinarides
No full textSeismogenic nodes - specific structures formed at the intersections of fault zones - have been identified in the Alps and Dinarides. The nodes have been delineated by the morphostructural zoning (MZ) method and their seismic potential has been evaluated by the pattern-recognition method. With MZ we have compiled a morphostructural map (scale 1:1,000,000) for the study region, using the GIS technology. The map shows the hierarchical block-structure of the region, the network of boundary zones bounding blocks, and the loci of the nodes. A three-level hierarchy has been established for the blocks and their boundaries. The recorded M ≥ 6.0 earthquakes nucleate at the nodes delineated by MZ, i.e. ignoring the seismic record. Among all delineated nodes we recognized the seismogenic ones (D), prone to M ≥ 6.0 earthquakes, with the pattern recognition algorithm CORA-3. The majority of these nodes is associated with the first and second rank boundaries, i.e. larger earthquakes originate at the boundaries of larger blocks. We have identified a number of D nodes, where strong earthquakes have not yet been recorded. In the Alps, these nodes form spatial clusters in the French-Italian Alps, in the Northern Calcareous Alps, in the Dolomites, and in the Karawanken. In the Dinarides, such nodes occur on the Adriatic coast and form two small clusters in the south and in the east of Serbia. The nodes capable of M ≥ 6.5 earthquakes are identified with the criteria of high seismicity nodes, previously derived from pattern recognition in the Pamirs-Tien Shan region. With these criteria we obtained satisfactory classification of the nodes for the Dinarides, while for the Alps the defined number of high seismic potential nodes is open to discussion
Relationships between magmatism and lithosphere-asthenosphere structure in the western Mediterranean and implications for geodynamics
No full textShear-wave (VS) tomography along transects across the Western- Central Mediterranean area reveals heterogeneous lateral and vertical physical characteristics in the lithosphere-asthenosphere system (LAS). A 50 km thick low velocity layer (LVL), with VS ∼ 4.0–4.2 km/sec, typical of low rigidity fluid-bearing mantle material, is observed at a depth of about 70–120 km from offshore Provence, to Sardinia and the Central Tyrrhenian Sea. This LVL, enclosed between higher velocity mantle rocks, rises to a depth of less than 30 km below the recent and active volcanoes of Central Italy and the Southern Tyrrhenian Sea, where a maximum in the heath flow is observed. The LVL is absent beneath Southeastern France and the northern border of the African foreland.
In the Balearic Sea-Sardinia-Central Tyrrhenian section, the depth of LVL corresponds to pressure conditions of minimum temperature of peridotite+CO2+H2 O solidus, consistent with conditions where fluid loss from the slab and mantle flow over the subducting plate favor significant melt gen- eration above steep, west-dipping subduction zones. It is suggested that LVLin the Balearic-Tyrrhenian domains is the result of mantle contamination and melting left behind by the eastward retreating Adriatic-Ionian subducting plates from Oligo-Miocene to present. This layer also marks a discontinuity between the lithospere and underlying mantle behind the subduction zone, favoring detachment and westward drift of the lithosphere, and consequent opening of backarc basins.
These data support the hypothesis that the orogenic Oligocene to Quater- nary volcanism in the Western Mediterranean area is the effect of shallow mantle processes, and argue against the presence of deep mantle plumes. A shallow-mantle origin is also suggested for the EM1-type Plio-Quaternary anorogenic magmatism in Sardinia and for the FOZO-DMM-type magmatism on the northern margin of the African foreland
High-Resolution Crustal S-wave Velocity Model and Moho Geometry Beneath the Southeastern Alps: New Insights From the SWATH-D Experiment
Full text linkWe compiled a dataset of continuous recordings from the temporary and permanent seismic networks to compute the high-resolution 3D S-wave velocity model of the Southeastern Alps, the western part of the external Dinarides, and the Friuli and Venetian plains through ambient noise tomography. Part of the dataset is recorded by the SWATH-D temporary network and permanent networks in Italy, Austria, Slovenia and Croatia between October 2017 and July 2018. We computed 4050 vertical component cross-correlations to obtain the empirical Rayleigh wave Green’s functions. The dataset is complemented by adopting 1804 high-quality correlograms from other studies. The fast-marching method for 2D surface wave tomography is applied to the phase velocity dispersion curves in the 2–30 s period band. The resulting local dispersion curves are inverted for 1D S-wave velocity profiles using the non-perturbational and perturbational inversion methods. We assembled the 1D S-wave velocity profiles into a pseudo-3D S-wave velocity model from the surface down to 60 km depth. A range of iso-velocities, representing the crystalline basement depth and the crustal thickness, are determined. We found the average depth over the 2.8–3.0 and 4.1–4.3 km/s iso-velocity ranges to be reasonable representations of the crystalline basement and Moho depths, respectively. The basement depth map shows that the shallower crystalline basement beneath the Schio-Vicenza fault highlights the boundary between the deeper Venetian and Friuli plains to the east and the Po-plain to the west. The estimated Moho depth map displays a thickened crust along the boundary between the Friuli plain and the external Dinarides. It also reveals a N-S narrow corridor of crustal thinning to the east of the junction of Giudicarie and Periadriatic lines, which was not reported by other seismic imaging studies. This corridor of shallower Moho is located beneath the surface outcrop of the Permian magmatic rocks and seems to be connected to the continuation of the Permian magmatism to the deep-seated crust. We compared the shallow crustal velocities and the hypocentral location of the earthquakes in the Southern foothills of the Alps. It revealed that the seismicity mainly occurs in the S-wave velocity range between ∼3.1 and ∼3.6 km/s
3D shear wave velocity model of the crust and uppermost mantle beneath the Tyrrhenian basin and margins
Full text linkThe Tyrrhenian basin serves as a natural laboratory for back-arc basin studies in the Mediterranean region. Yet, little is known about the crust-uppermost mantle structure beneath the basin and its margins. Here, we present a new 3D shear-wave velocity model and Moho topography map for the Tyrrhenian basin and its margins using ambient noise cross-correlations. We apply a self-parameterized Bayesian inversion of Rayleigh group and phase velocity dispersions to estimate the lateral variation of shear velocity and its uncertainty as a function of depth (down to 100 km). Results reveal the presence of a broad low velocity zone between 40 and 80 km depth affecting much of the Tyrrhenian basin's uppermost mantle structure and its extension mimics the paleogeographic reconstruction of the Calabrian arc in time. We interpret the low-velocity structure as the possible source of Mid-Ocean Ridge Basalts- and Ocean Island Basalts- type magmatic rocks found in the southern Tyrrhenian basin. At crustal depths, our results support an exhumed mantle basement rather than an oceanic basement below the Vavilov basin. The 3D crust-uppermost mantle structure supports a present-day geodynamics with a predominant Africa-Eurasia convergence
Geophysical and petrological modeling of the structure and composition of the crust and upper mantle in complex geodynamic settings: The Tyrrhenian Sea and surroundings.
No full textIntegrated petrological-geophysical studies are useful in a geodynamically complex area characterised by abundant variable young magmatism, such as the Tyrrhenian Sea and surroundings. A thin crust overlying a soft mantle is observed for volcanoes in the Central Tyrrhenian Sea. The structure of the upper mantle, in contrast, shows striking differences among various volcanic provinces. The petrological–geochemical signatures of Italian volcanoes show strong variations that allow us to distinguish several magmatic provinces. These often coincide with mantle sectors identified by Vs tomography. The dominance of mafic subalkaline magmatism in the Tyrrhenian Sea basin denotes large degrees of partial melting, well in agreement with the soft characteristics of the uppermost mantle in this area. Petrological-geophysical constraints allows us to propose a 3D geodynamic model of the Tyrrhenian basin and bordering volcanic areas, including the subduction of the Ionian–Adria lithosphere
- …
