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Bianchi, Irene
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Bianchi, Irene
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irene.bianchi@univie.ac.at
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22 results
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- PublicationRestrictedEvidence for the contemporary magmatic system beneath Long Valley Caldera from local earthquake tomography and receiver function analysis(2011)
; ; ; ; ; ;Seccia, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Bianchi, I.; Institut für Meteorologie und Geophysik, Universität Wien, Vienna, Austria ;Hill, D.; U.S. Geological Survey, Menlo Park, California, USA; ; ; ; We present a new P wave and S wave velocity model for the upper crust beneath Long Valley Caldera obtained using local earthquake tomography and receiver function analysis. We computed the tomographic model using both a graded inversion scheme and a traditional approach. We complement the tomographic Vp model with a teleseismic receiver function model based on data from broadband seismic stations (MLAC and MKV) located on the SE and SW margins of the resurgent dome inside the caldera. The inversions resolve (1) a shallow, high‐velocity P wave anomaly associated with the structural uplift of a resurgent dome; (2) an elongated, WNW striking low‐velocity anomaly (8%–10 % reduction in Vp) at a depth of 6 km (4 km below mean sea level) beneath the southern section of the resurgent dome; and (3) a broad, low‐velocity volume (∼5% reduction in Vp and as much as 40% reduction in Vs) in the depth interval 8–14 km (6–12 km below mean sea level) beneath the central section of the caldera. The two low‐velocity volumes partially overlap the geodetically inferred inflation sources that drove uplift of the resurgent dome associated with caldera unrest between 1980 and 2000, and they likely reflect the ascent path for magma or magmatic fluids into the upper crust beneath the caldera.161 46 - PublicationRestrictedDeep structural heterogeneities and the tectonic evolution of the Abruzzi region (Central Apennines, Italy) revealed by microseismicity, seismic tomography, and teleseismic receiver functions(2010-05-21)
; ; ; ; ; ;Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Bagh, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Bianchi, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Barchi, M.; ; ; ; The crustal structure of central Apennines (Italy) is still poorly defined, leaving uncertainties on the tectonic style (thin or thick-skinned) responsible for the development of the thrust-and-fold belt. The today active extension, which replaced compression since early Quaternary, is presumably in"uenced by the pre-existing structure that yields location and segmentation of the fault system. To focus on such issues, we computed P and S-wave velocity models of the crust by using the independent methodologies of local earthquakes tomography and teleseismic receiver function. We document strong lateral and vertical heterogeneities that define shallow, imbricate sheets of the Mesozoic cover that overlay exceptionally high Vp and high Vs bodies. These bodies can be interpreted as either dolomitic or, partially hydrated, ma!c rocks. The two alternative interpretations respectively imply an ultra-thick deposition of dolomitic rocks in the hanging wall of Triassic normal fault or a deep exhumation of the Pre-Mesozoic basement during the early Mesozoic sin-rift tectonic. In both cases, these bodies in"uenced the evolution of the thrust-and-fold belt. Very remarkably, active normal faults, like those ruptured during the still ongoing 2009 L'Aquila sequence, concentrate at the border of these bodies, suggesting that they have an active role in the segmentation of the normal fault system. The rheological behavior of such high Vp high Vs bodies, weak or strong, is still uncertain, but of utmost importance to understand the risk of future normal faulting earthquakes.272 38 - PublicationOpen AccessMoho topography beneath the European Eastern Alps by global-phase seismic interferometryIn this work we present the application of the global-phase seismic interferometry (GloPSI) technique to a dataset recorded across the Eastern Alps with the EASI (Eastern Alpine Seismic Investigation) temporary seismic network. GloPSI aims at rendering an image of the lithosphere from the waves that travel across the core before reaching the seismic stations (i.e. PKP, PKiKP, PKIKP). The technique is based on the principle that a stack of autocorrelations of transmission responses mimics the reflection response of a medium and is used here to retrieve information about the crust–mantle boundary, such as its depth and topography. We produce images of the upper lithosphere using 64 teleseismic events. We notice that with GloPSI, we can well image the topography of the Moho in regions where it shows a nearly planar behaviour and corresponds to a strong velocity contrast (i.e. in the northern part of the profile, from the Bohemian Massif to the Northern Calcareous Alps). Below the higher crests of the Alpine chain, and the Tauern Window in particular, we cannot find evidence of the boundary between crust and mantle. The GloPSI results indicate the absence of an Adriatic crust made of laterally continuous layers smoothly descending southwards and confirm the observations of previous studies suggesting a structurally complex and faulted internal Alpine crustal structure.
52 14 - PublicationOpen AccessCrustal structure and deformation across a mature slab tear zone: the case of southern Tyrrhenian subduction (Italy)(2016-11)
; ; ; ; ; ; ; ; ; We compute S velocity profiles of the crust across the Messina Strait (Italy), the tear zone at the southern end of the Ionian subduction zone. Separating Sicily from Calabria, the Messina Strait hosted some of the strongest earthquakes to ever occur in Italy. Here the motion of the Ionian slab with respect to Sicily creates a complex tectonic setting characterized by lithospheric tearing. We show velocity models of the crust, computed from teleseismic receiver function inversion, outlining the differences between Sicily and Calabria. Strong deformation across the Messina Strait between 10–15 and 30 km depth is expressed by strong anisotropy (up to 10%), developed in a ductile shear zone of the crust. The top of these ductile weaker layers could limit the depth extent of future ruptures.243 97 - PublicationOpen AccessLa campagna sismica del progetto Alto Lazio: rapporto delle attività 2008-2009(2011-03-04)
; ; ; ; ; ; ;Anselmi, Mario; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Buttinelli, Mauro; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bianchi, Irene; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Colasanti, Gianfranco; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Chiarabba, Claudio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Quattrocchi, Fedora; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; 223 438 - PublicationRestrictedFluid migration in continental subduction: The Northern Apennines case study(2011)
; ; ; ; ;Agostinetti, N. P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Bianchi, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Amato, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; ; ; Subduction zones are the place in the world where fluids are transported from the foredeep to the mantle and back-to-the-surface in the back-arc. The subduction of an oceanic plate implies the transportation of the oceanic crust to depth and its methamorphization. Oceanic sediments release water in the (relatively) shallower part of the subduction zone, while dehydration of the subducted basaltic crust allows fluid circulation at larger depths. While the water budget in oceanic subduction has been deeply investigated, less attention has been given to the fluids implied in the subduction of a continental margin (i.e. in continental subduction). In this study, we use teleseismic receiver function (RF) analysis to image the process of water migration at depth, from the subducting plate to the mantle wedge, under the Northern Apennines (NAP, Italy). Harmonic decomposition of the RF data-set is used to constrain both isotropic and anisotropic structures. Isotropic structures highlight the subduction of the Adriatic lower crust under the NAP orogens, from 35–40 km to 65 km depth, as a dipping low S-velocity layer. Anisotropic structures indicate the presence of a broad anisotropic zone (anisotropy as high as 7%). This zone develops in the subducted Adriatic lower crust and mantle wedge, between 45 and 65 km depth, directly beneath the orogens and the more recent back-arc extensional basin. The anisotropy is related to the metamorphism of the Adriatic lower crust (gabbro to blueschists) and its consequent eclogitization (blueschists to eclogite). The second metamorphic phase releases water directly in the mantle wedge, hydrating the back-arc upper mantle. The fluid migration process imaged in this study below the northern Apennines could be a proxy for understanding other regions of ongoing continental subduction.183 29 - PublicationOpen AccessMantle upwelling beneath the Apennines identified by receiver function imaging(2020-11-12)
; ; ; ; ; ; ; Magmatism, uplift and extension diffusely take place along collisional belts. Even though links between mantle dynamics and shallow deformation are becoming more evident, there is still poor understanding of how deep and surface processes are connected. In this work, we present new observations on the structure of the uppermost mantle beneath the Apennines belt. Receiver functions and seismic tomography consistently define a broad zone in the shallow mantle beneath the mountain belt where the shear wave velocities are lower than about 5% and the Vp/Vs ratio is higher than 3% than the reference values for these depths. We interpret these anomalies as a pronounced mantle upwelling with accumulation of melts at the crust-mantle interface, on top of which extensional seismicity responds to the crustal bending. The melted region extends from the Tyrrhenian side to the central part of the belt, with upraise of fluids within the crust favored by the current extension concentrated in the Apennines mountain range. More in general, mantle upwelling, following detachment of continental lithosphere, is a likely cause for elevated topography, magmatism and extension in post-collisional belts.109 12 - PublicationOpen AccessUpper crustal structure at the KTB drilling site from ambient noise tomographyIn this study, we show results from ambient noise tomography around the KTB (Kontinentales Tiefbohrprogramm der Bundesrepublik Deutschland), a continental deep drilling site located at the western edge of the Bohemian Massif, within the Variscan belt of Europe. At the KTB site, crustal rocks have been drilled down to 9 km depth. Before the drilling activity started, several active seismic surveys had been performed to explore its surroundings during the 1980s and early 1990s, in the frame of an extensive exploration of the area aimed at unravelling the characteristics of the continental lower crust that is exposed at surface in this location. Despite the exploration campaigns held at and around the KTB drilling site, there are important targets that are worth further investigation; these are related in particular to the obduction of lower crustal units to the surface, and to the mechanism of orogenic processes in general. Here we present a new 3-D shear wave velocity model of the area from cross-correlations of ambient seismic noise. The model is obtained by a unique data set composed of 2 yr of continuous data recorded at nine 3-component temporary stations (installed from July 2012 to July 2014) located on top and around the drilling site, and together with the data from 19 permanent stations throughout the region. This paper is focusing on the upper crustal layers, and we show velocity variations at short scales that correlate well with known geological structures in the region of the KTB site, at the surface and at depth. These are used to discuss features that are less well-resolved at present.
28 31 - PublicationOpen AccessConstraining the Moho Depth Below Bhutan With Global-Phase Seismic InterferometryWe use a novel technique named global-phase seismic interferometry (GloPSI) to image the lithospheric structure, and in particular the Moho, below two parallel north-south transects belonging to the GANSSER network (2013–2014). The profiles cross the Himalayan orogenic wedge in Bhutan, a tectonically important area within the largest continent-continent collision zone on Earth that is still undergoing crustal thickening and represents a challenging imaging target for the GloPSI approach. GloPSI makes use of direct waves from distant earthquakes and receiver-side reverberations with near vertical incidence. Reflections are isolated from earthquake recordings by solving a correlation integral and are turned into a reflectivity image of the lithosphere below the arrays. Our results compare favorably with first-order features observed from a previous receiver function (RF) study. We show that a combined interpretation of GloPSI and RF results allows for a more in-depth understanding of the lithospheric structure across the orogenic wedge in Bhutan.
44 21 - PublicationRestrictedDeep structure of the Colli Albani volcanic district (central Italy) from receiver functions analysis(2008-09-24)
; ; ; ; ;Bianchi, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Piana Agostinetti, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; ; ; The Colli Albani is a Quaternary quiescent volcano, located a few kilometers southeast of Rome (Italy). During the past decade, seismic swarms, ground deformation, and gas emissions occurred in the southwestern part of the volcano, where the last phreatomagmatic eruptions (27 ka) developed, building up several coalescent craters. In the frame of a Dipartimento Protezione Civile – Istituto Nazionale di Geofisica e Vulcanologica project aimed at the definition and mitigation of volcanic hazard, a temporary array of seismic stations has been deployed on the volcano and surrounding areas. We present results obtained using receiver functions analysis for eight stations, located upon and around the volcanic edifice, and revealing how the built of the volcanic edifice influenced the prevolcanic structures. The stations show some common features: the Moho is almost flat and located at 23 km, in agreement with the thinning of the Thyrrenian crust. Also the presence of a shallow limestone layer is a stable feature under every station, with a variable thickness between 4 and 5 km. However, some features change from station to station, indicating a local complexity of the crustal structure: a shallow discontinuity dividing the Plio-Pleistocene sediments by the Meso-Cenozoic limestones, and a localized anisotropic layer, in the central part of the old structure, which points of the deformation of the limestones. Other two strongly anisotropic layers are detected under the stations in lower crust and upper mantle, with symmetry axis directions related to the evolution of the volcano complex.230 40
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