http://hdl.handle.net/2122/216 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/6036 Titolo: Predicting the impact of lava flows at Mount Etna, Italy<br/><br/>Autori: Crisci, G.; Department of Earth Sciences, University of Calabria, 87036 Rende, Italy; Avolio, M. V.; Department of Mathematics, University of Calabria, 87036 Rende, Italy; Behncke, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; D'Ambrosio, D.; Department of Mathematics, University of Calabria, 87036 Rende, Italy; Di Gregorio, S.; Department of Mathematics, University of Calabria, 87036 Rende, Italy; Lupiano, V.; Department of Earth Sciences, University of Calabria, 87036 Rende, Italy; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Romgo, R.; Department of Earth Sciences, University of Calabria, 87036 Rende, Italy; Spataro, W.; High Performance Computing Centre, University of Calabria, 87036 Rende, Italy<br/><br/>Abstract: Forecasting the time, nature, and impact of future eruptions is difficult at volcanoessuch as Mount Etna, in Italy, where eruptions occur from the summit and on the flanks,affecting areas distant from each other. Nonetheless, the identification and quantificationof areas at risk from new eruptions are fundamental for mitigating potential humancasualties and material damage. Here, we present new results from the application of amethodology to define flexible high‐resolution lava invasion susceptibility maps based ona reliable computational model for simulating lava flows at Etna and on a validationprocedure for assessing the correctness of susceptibility mapping in the study area.Furthermore, specific scenarios can be extracted at any time from the simulation database,for land use and civil defense planning in the long term, to quantify, in real time, theimpact of an imminent eruption, and to assess the efficiency of protective measures. Wed, 28 Apr 2010 00:00:00 GMT http://hdl.handle.net/2122/6035 Titolo: Insights into fluid circulation across the Pernicana Fault (Mt. Etna, Italy) and implications for flank instability<br/><br/>Autori: Siniscalchi, A.; Dipartimento di Geologia e Geofisica, Università degli Studi di Bari, via Orabona, 4-70125, Bari-Italy; Tripaldi, S.; Dipartimento di Geologia e Geofisica, Università degli Studi di Bari, via Orabona, 4-70125, Bari-Italy; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Giammanco, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Piscitelli, S.; Istituto di Metodologie per l' Analisi Ambientale, CNR, Tito (PZ), Italy; Balasco, M.; Istituto di Metodologie per l' Analisi Ambientale, CNR, Tito (PZ), Italy; Behncke, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Magri, C.; Dipartimento di Geologia e Geofisica, Università degli Studi di Bari, via Orabona, 4-70125, Bari-Italy; Naudet, V.; Université Bordeaux 1, Geosciences Hydrosciences Material and Constructions, GHYMAC-EA 4134, Talence, F-33405, France; Rizzo, E.; Istituto di Metodologie per l' Analisi Ambientale, CNR, Tito (PZ), Italy<br/><br/>Abstract: We conducted geophysical–geochemical measurements on a ∼2 kmN–S profile cutting across the PernicanaFault, one of the most active tectonic features on the NE flank of Mt. Etna. The profile passes from theunstable E flank of the volcano (to the south) to the stable N flank and significant fluctuations in electricalresistivity, self-potential, and soil gas emissions (CO2, Rn and Th) are found. The detailed multidisciplinaryanalysis reveals a complex interplay between the structural setting, uprising hydrothermal fluids, meteoricfluids percolating downwards, ground permeability, and surface topography. In particular, the recoveredfluid circulation model highlights that the southern sector is heavily fractured and faulted, allowing theformation of convective hydrothermal cells. Although the existence of a hydrothermal system in a volcanicarea does not surprise, these results have great implications in terms of flank dynamics at Mt. Etna. Indeed,the hydrothermal activity, interacting with the Pernicana Fault activity, could enhance the flank instability.Our approach should be further extended along the full extent of the boundary between the stable andunstable sectors of Etna for a better evaluation of the geohazard in this active tectonic area. Thu, 01 Apr 2010 00:00:00 GMT http://hdl.handle.net/2122/5907 Titolo: Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska)<br/><br/>Autori: Meneghini, F.; Pisa Univ.; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Rowe, D. C.; Univ. Santa Cruz, USA; Moore, C.; Univ. Santa Cruz, USA; Tsutsumi, A.; Kyoto Univ. Japan<br/><br/>Abstract: Abstract: On Kodiak Island (Alaska), decimeter-thick black fault rocks (BFR) are at the core of 10'smeters-thick foliated cataclasites. Cataclasites belong to mélanges regarded as paleo-décollementactive at 12-14 km depth and 230-260oC. Each black layer is mappable for tens of meters along strike.The BFR feature a complex layering made at microscale by alternation of granular and crystallinemicrotextures, composed of micron-scale sub-rounded quartz and plagioclase in an ultrafine,phyllosilicate-rich matrix. In the crystalline microlayers, tabular zoned microlites of plagioclase makemuch of the matrix. No such feldspars are found in the cataclasite. We interpret crystalline microlayersas pseudotachylytes. The granular microlayers show higher grain size variability, crushed microlitesand textures typical of fluidization and granular flow deformation. Crosscutting relationships betweengranular and crystalline microlayers include flow and intrusion structures and mutual brittletruncation. This suggests that each 10's centimeter-thick composite BFR record multiple pulses ofseismic slip. In each pulse, ultracomminuted fluidized material and friction melt formed and deformedtogether in a ductile fashion. Brittle truncation by another pulse occurred after solidification of thefriction melt and the fluidized rock.XRPD and XRF analyses show that BFR have similar mineral composition and chemical content as thecataclasites. The observed systematic chemical differences cannot be explained by bulk or preferentialmelting of any of the cataclasite components. The presence of an open, fluid-infiltrated system withBFR later alteration is suggested. The geochemical results indicate that these subduction-relatedpseudotachylytes, differ from those typically described in crystalline rocks and other tectonic settings. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/5906 Titolo: First evidence of hexagonal anorthite in pseudotachylyte: a new tool to constrain the thermal history during a seismic event<br/><br/>Autori: Nestola, F.; Univ. Padova; Mittempergher, S.; Univ. Padova; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: The determination of the maximum temperature achieved by friction melt (Tmelt) in pseudotachylyte-bearing faults is crucial to estimate earthquake source parameters (e.g., earthquake energy budgets, coseismicfault strength) on a geological basis. Here we investigated the mineralogy of a pseudotachylyte from the Gole Larghe Fault (Italian Alps) by using X-ray powder diffraction, micro-Raman spectroscopy,and EDS-equipped field emission scanning electron microscopy. In particular, we report the presence of the hexagonal polymorph of CaAl2Si2O8 (dmisteinbergite) in a pseudotachylyte. Published experimental work shows dmisteinbergite can crystallize at 1200–1400 °C by rapid quenching. Therefore, the presence of dmisteinbergite in pseudotachylyte could be a reliable geothermometer for friction melts for which Tmelt has only as yet been estimated. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/5905 Titolo: Rough Faults, Distributed Weakening, and Off-Fault Deformation<br/><br/>Autori: Griffith, A. W.; Akron Univ. Ohio; Nielsen, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Smith, F. A. S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: We report systematic spatial variations of fault rocks along non-planar strike-slip faults 11 cross-cutting the Lake Edison Granodiorite, Sierra Nevada, California (Sierran wavy fault) and 12 Lobbia outcrops of the Adamello Batholith in the Italian Alps (Lobbia wavy fault). In the case of 13 the Sierran fault, pseudotachylyte formed at contractional fault bends, where it is found as thin 14 (1-2 mm) fault-parallel veins. Epidote and chlorite developed in the same seismic context as the 15 pseudotachylyte and are especially abundant in extensional fault bends. We argue that the 16 presence of fluids, as illustrated by this example, does not necessarily preclude the development 17 of frictional melt. In the case of the Lobbia fault, pseudotachylyte thickness varies along the 18 length of the fault, but the pseudotachylyte veins thicken and pool in extensional bends. We 19 conduct a quantitative analysis of fault roughness, microcrack distribution, stress, and friction 20 along the Lobbia fault. 21Numerical modeling results show that opening in extensional bends and localized thermal 22 weakening in contractional bends counteract resistance encountered by fault waviness, resulting 23 in an overall weaker fault than suggested by the corresponding static friction coefficient. The 24 models also predict static stress redistribution around bends in the faults which are consistent 25 with distributions of microcracks, indicating significant elastic and inelastic strain energy is 26 dissipated into the wall rocks due to non-planar fault geometry. Together these observations suggest that damage and energy dissipation occurs along the entire non-planar fault during slip, 28 rather than being confined to the region close to the dynamically propagating crack tip. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/2122/5904 Titolo: The effects of fault orientation and fluid infiltration on fault rock assemblages at seismogenic depths<br/><br/>Autori: Mittempergher, S.; Padova Univ.; Pennacchioni, G.; Padova Univ.; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: The factors controlling the development of different types of fault rock assemblages and, more specifically,the formation of friction melts are still not fully understood. In this study we compared twoexhumed strike–slip faults in the Adamello batholith (Southern Alps): the Gole Larghe and the PassoCercen fault zones, active at 9–11 km depth and temperatures of 250–300 C. Each fault zone consists ofhundreds of sub-parallel strands exploiting pre-existing joints. The Gole Larghe fault strikes N105 5 and is dextral; the fault rocks are cataclasites and widespread, centimetre-thick pseudotachylytes. ThePasso Cercen fault strikes on average N130 and is formed by multiple fault horizons: fault segmentsstriking N105 –N130 are mainly dextral, whereas faults striking N135 –N140 are mainly sinistral.Microstructural, mineralogical and geochemical investigations show that the fault rocks are cataclasitesassociated with thick epidote þ K-feldspar þ quartz veins and rare, millimetre-thick pseudotachylytes.Field evidence suggests that in both fault zones, the direction of the maximum horizontal stress s1 wasN135 . The Gole Larghe fault strikes at about 30 to s1 and is favourably oriented for reactivation. Bycontrast, the Passo Cercen fault strikes at low angles to s1 and is unfavourably oriented for reactivation,therefore requiring the development of high pore pressures, as suggested by the occurrence of extensiveepidote veining and hydraulic breccias. It is proposed that frictional melting in the Passo Cercen faultzone was inhibited by the development of high pore pressures and low effective normal stresses. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/2122/5903 Titolo: Static stress drop associated with brittle slip events on exhumed faults.<br/><br/>Autori: Griffith, A. W.; Akron Univ. Ohio; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Pennacchioni, G.; Padova Univ.; Pollard, D. D.; Stanford Univ.; Nielsen, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: We estimate the static stress drop on small exhumed strike-slip faults in the LakeEdison granodiorite of the central Sierra Nevada (California). The subvertical strike-slipfaults were exhumed from 4 to 15 km depth and were chosen because they are exposed inoutcrop along their entire tip-to-tip lengths of 8–12 m. Slip nucleated on joints andaccumulated by crystal-plastic shearing (forming quartz mylonites from early quartz veinfilling in joints) and successive brittle faulting (forming epidote-bearing cataclasites).The occurrence of thin, 300 mm wide, pseudotachylytes along some small faultsthroughout the study area suggests that some, if not all, of the brittle slip on the study areafaults may have been seismic. We suggest that the contribution of brittle, cataclastic slip tothe total slip along the studied cataclasite-bearing small faults may be estimated by thelength of epidote-filled, rhombohedral dilatational jogs (rhombochasms) distributedquasi-periodically along the length of the faults. The interpretation that slip recorded byrhombochasms occurred in single events is based on evidence that (1) epidote crystalsare randomly oriented and undeformed within the rhombochasm; (2) cataclasite inprincipal slip zones does not include clasts of previous cataclasite, and (3)rhombochasm lengths vary systematically along the length of the faults with slipmaximum occurring near the fault center, tapering to the fault tips. We thereby constrainboth the rupture length and slip. On the basis of these measurements, we calculate stressdrops ranging over 90–250 MPa, i.e., one to two orders of magnitude larger thantypical seismological estimates for earthquakes, but similar in magnitude toseismological estimates of small (<M2) earthquakes from the San Andreas FaultObservatory at Depth (SAFOD). The slip events described in the present study occurredalong small, deep-seated faults, and, given the calculated stress drops and observationsthat brittle faults exploited joints sealed by quartz-bearing mylonite, we concludethat these were ‘‘strong’’ faults. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/2122/5902 Titolo: Seismic tremor in subduction zones: the rock-physics evidence<br/><br/>Autori: Burlini, L.; ETH Zurich; Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Meredith, P.; ICL London<br/><br/>Abstract: Episodic tremor and slip (ETS) have been correlatedwith rupture phenomena in subducting oceanic lithosphereat 30–45 km depth, where high VP/VS ratios, whichsuggest high-fluid pressures, have been observed. ETS,by accommodating slip in the down-dip portion of thesubduction zone, may trigger megathrust earthquakes up-dipin the locked section. During dehydration experiments onserpentinite (typical rock of the oceanic lithosphere) attemperatures found in nature at 30–45 km depth (400–550 C), we observe seismic signals in the form of acousticemissions that closely resemble low frequency earthquakes,seismic tremor and regular earthquakes. Our findings supportthe concept that water released during dehydration reactionsincreases the pore pressures and can trigger ETS and regularearthquakes by reducing slip resistance. Citation: Burlini, L.,G. Di Toro, and P. Meredith (2009), Seismic tremor in subductionzones: Rock physics evidence, Geophys. Res. Lett., 36, L08305,doi:10.1029/2009GL037735. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/2122/5772 Titolo: Messinian-Early Pliocene crustal shortening along the Tyrrhenian margin of Tuscany, Italy<br/><br/>Autori: Sani, F.; Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Florence, Italy; Bonini, M.; CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, U.O. Firenze, Florence, Italy; Cerrina Feroni, A.; CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, Pisa, Italy; Mazzarini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Moratti, G.; CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, U.O. Firenze, Florence, Italy; Musumeci, G.; Dipartimento di Scienze della Terra, Università degli Studi di Pisa, Pisa, Italy; Corti, G.; CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, U.O. Firenze, Florence, Italy; Iatta, F.; Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Florence, Italy; Ellero, A.; CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, Pisa, Italy<br/><br/>Abstract: This paper illustrates the results of structural studies carried out in the western margin of Tuscany along a major crustal structure. Surface deformation of sediments filling different basins aligned on top of this major structure (from north to south: the Fine Basin, the Sassa–Guardistallo basin, the Rio Guardigiano area in the Lustignano basin) allow us to date its tectonic activity to the Messinian-Early Pliocene. In these areas, structures such as reverse and strike-slip faults and mesoscopic folds are widely developed. Structural analysis determined a compressive stress field with the σ1 oriented from E-W to NE-SW active from Messinian to Early Pliocene. At the southern end of this crustal structure, the Gavorrano antiform and the granitic pluton (radiometric age of granite ~4.4 Ma) coring this fold correlate with a thrust ramp anticline at depth, and thus constrain thrust activity to the Early Pliocene. These data document a Messinian–Early Pliocene compressive activity that contrasts with models invoking continuous extensional tectonics affecting the hinterland since the Late Oligocene-Middle Miocene in the frame of a back-arc-slab retreating process. The results presented therefore raise the question of which geodynamical model could account for such a complex structural evolution of Northern Apennines hinterland. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/2122/5722 Titolo: Relations between deformation and upper crustal magma emplacement in laboratory physical models<br/><br/>Autori: Mazzarini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Musumeci, G.; Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy; Montanari, D.; Centro di Eccellenza per la Geotermia di Larderello, Larderello (PI), Italy; Corti, G.; Istituto di Geoscienze e Georisorse, CNR, Firenze, Italy<br/><br/>Abstract: This paper presents analogue models for the emplacement of granitic magmas in upper crustal levels with different mechanical layering during shortening, extension and strike–slip deformation. In particular, we investigated how a weak layer embedded in the upper brittle crust can control the level of magma emplacement. The adopted experimental setup was used to examine the control of soft rocks on the movement of magma through a deforming brittle crust. Model results indicate that the occurrence of a weak (soft) layer embedded in brittle (stiff) material has an impact on the level of magma emplacement. The level of emplacement during both extension and shortening was systematically deeper for models with a soft layer than for purely brittle models. During strike–slip deformation the magma pierced the surface in both purely brittle and brittle–ductile models. Thu, 01 Jan 2009 00:00:00 GMT