ALBERT

Description: Field geology, well data and seismic imaging have illuminated the upper crustal structure of the Southern Apennines. However, lack of control of the deep structure allows viable competing thin-skin and thick-skin models of the orogen. In thin-skin models the detachment decouples a stack of rootless nappes from the basement. In thick-skin models, basement is involved in the most recent phase of thrusting. To examine the deep crustal structure, we use the teleseismic recordings from the CAT/SCAN array, deployed in southern Italy from Dec. 2003-Oct. 2005. We use receiver functions processed into a Common Conversion Point stack to generate images of the crust. We image three main westward-dipping seismic-velocity discontinuities where P-to-S conversions occur. They correspond to velocity jumps at the Moho, the upper-lower crust boundary and sedimentary interfaces resulting from the contrast between clastic and carbonate strata with basement. The CCP image matches features from both thin-skin and thick skin model. The lateral continuity of the converters favors thin skin, but consistent interpretation across the image favors the thick skin. Overall, the results provide a better fit to the thick-skin interpretation. This suggests a change in structural style as the collision with Apulia halted motion. This model also implies considerably less Plio-Pleistocene shortening across the Apennines and a SE motion of the Calabrian Arc subparallel to the southern Apennines rather than a radial expansion of the Arc.

Description: Published

Description: AGU General Assembly, S. Francisco

Description: 3.3. Geodinamica e struttura dell'interno della Terra

Description: open

Description: We analyze the seismicity of a small sector of the Northern Apennines merging data from the Italian seismic bulletin with original data collected by temporary seismic networks. Our attention is focused on the region enclosed between the Apenninic watershed and the Adriatic Sea. This portion of belt is interested by the occurrence of diffuse crustal seismicity and small-to-moderate earthquakes. In this paper we study the five small sequences with mainshock having Mw 〈 4.7 that in the past 15 years hit the area. Our interest is addressed to better understand the relationship between these events and the regional seismotectonic setting in terms of seismicity distribution and stress field. Two regions with different behavior in the seismic release can be distinguished: (i) along the watershed where seismicity is clustered at shallow depths (〈 15 km) and where strong earthquakes occurred in the past, (ii) an eastern portion where the seismicity is distributed across all of the crustal volume, locally reaching depths down to 30 km. The focal mechanism of the seismic sequences shows mainly normal fault kinematics coherent with the regional stress field. Detailed stress field analysis suggests a rotation of the principal stress axis moving from the axial part of the chain toward the Adriatic Sea to the east.

Description: Published

Description: 136-144

Description: 1.1. TTC - Monitoraggio sismico del territorio nazionale

Description: 3.2. Tettonica attiva

Description: JCR Journal

Description: reserved

Description: Global crustal model, from gravity studies, imaged a thick crust (〉40 km) under Eastern Antartic craton (EAC). This global trend ends abruptly west of the Transantarctic Mountains (TAM), which border EAC along its western margins. There, the crust raises up to about 20 km. While this model points out the difference between EAC and the Ross sea crustal structures, its intrinsic spatial resolution gives little help to solve some regional geophysical issues, like the TAM orogenesis and the formation and nature of the Wilkes Basin. In this study, teleseismic Receiver Functions (RFs) are used to image the S-velocity crustal structure in finer details. We computed RFs from teleseismic events recorded during three different austral summer compaigns: BackTAM, WIBEM and WISE. Broadband seismic stations were deployed along a transect which spans from the coast of Northern Victoria land (NVL) to the far interior of the EAC plateau. The transect, almost perpendicular to the regional TAM axis, came across four different geological/geophysical settings: the alloctonhous terranes of the NVL, the TAM sector, the Wilkes Basin and the EAC plateau. Each area shows peculiar crustal structures and we propose both finer local S-velocity models and a regional crustal model.

Description: Published

Description: AGU General Assembly, S. Francisco

Description: 3.3. Geodinamica e struttura dell'interno della Terra

Description: open

Description: The main goal of this study is to increase the understanding of the physical mechanisms behind the ongoing seismic activity in the Pollino area and its influence on the seismic hazard of the Apennines-Calabrian arc boundary region. The study area, near the Pollino massif, is located at the northernmost edge of the Calabrian Arc, which is the last oceanic subduction segment along the Africa-Eurasian plate. The subduction results from the sinking of the Ionian oceanic plate beneath the Calabrian Arc-Southern Tyrrhenian Sea and is part of the fragmented tectonic boundary between two macro-plates: Africa and Eurasia. The subduction geometry is well-documented by several seismological studies (i.e. Chiarabba et al., 2005), and the lithospheric structure of the area is quietly well known (i.e. Totaro et al., 2014 and Piana Agostinetti and Amato, 2009) Despite the slow N-S convergence between these major plates, the Southern Tyrrhenian Sea is a large basin characterized by E-W extensional tectonic. Since Late Miocene, the Calabrian Arc slab experienced rapid rollback, moving E to SE at a rate of 5-6 cm/yr, which is by far higher than the ~1-2 cm/yr rate of convergence between Africa and Europa (Faccenna et al., 2004). However, during late Pleistocene, rollback and subduction have slowed and is likely proceeding at less than 1 cm/yr (D’Agostino and Selvaggi., 2004). Geodetic measurements show that the Pollino Range is subject to NE-SW anti-apenninic extension. In the region the strain rate field shows a continuous belt of extensional deformation that follows the ridge of the Southern Apennines and extends in the Pollino region. The extension rate appears to decrease from the Southern Apennines to the Calabria- Lucania border region (D’Agostino et al., 2013). This finding indeed reveals that the Pollino region is deforming and accumulating tectonic strain which results in a complex system of normal active faults striking sub-parallel to the Apennines. Two principal normal faults are present in the Italian Database of the Individual Seismogenic Sources DISS version 3.1.1 (DISS Working Group, 2010) in the Pollino area: the Pollino (P) fault and the “Rimendiello-Mormanno” (RM) fault system. The RM fault is an active seismogenic structure it strikes about NNW-SSE and dips toward NE; it has hosted in its northernmost part a M 5.0 earthquake on 9th September 1998. The P fault has similar strike but dips toward SW: it shows no recent seismicity and is hence one of the most prominent seismic gaps in the Italian historical seismic catalogue (Rovida et al., 2011). Paleoseismic studies have shown that the P fault was active in the last ten thousand years and is capable to produce events with magnitude above 6.0. The DISS database reports as debated source also the Piana Perretti fault (Brozzetti et al., 2009). A detailed structural map of the area interested by the seismic sequence shows three fault systems (Brozzetti et al., 2013) consisting of several aligned fault segments that have been active during the Late Pleistocene and are reasonably presently active. The first fault system strikes NW-SE and dips toward SW (including the Piana Perretti fault at the NE edge of the Mercure Basin), the second one has similar strike and NE dip, while the third one strikes about E-W. Earthquakes reported in the historical catalogues for this area are not very strong. Few earthquakes with magnitude probably less than 6 affected the area, including the Mw=5.6 “Mercure” event in 1998 (Brozzetti et al., 2009). The Parametric Catalogue of Italian earthquakes (CPTI11, Rovida et al., 2011), shows very well the lack of strong earthquakes in the region: there is a clear evidence of large earthquakes in the Campania-Basilicata area (M~7.0) and several strong earthquakes in the Sila region and in the whole Calabrian territory. According to the seismic classification of the national territory, the area affected by the 2010-2014 seismic activity have a relatively higher probability to be shaken by a strong acceleration (Gruppo di Lavoro MPS, 2004). Most of the seismic events occurred in areas where the peak ground acceleration having 10% chance of being exceeded in next 50 years is between the values of 0.225 g and 0.275 g.

Description: Published

Description: Bologna

Description: 2T. Tettonica attiva

Description: 3T. Pericolosità sismica e contributo alla definizione del rischio

Description: 5T. Sorveglianza sismica e operatività post-terremoto

Description: 1IT. Reti di monitoraggio e Osservazioni

Description: open