http://hdl.handle.net/2122/194 2013-05-23T10:53:41Z http://hdl.handle.net/2122/7958 Title: Project S1: Analysis of the seismic potential in Italy for the evaluation of the seismic hazard Authors: Barba, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Doglioni, C.; Sapienza Università di Roma Abstract: The project S1 was aimed at (a) collecting new data and to update the existing databases needed to quantify seismic hazard; (b) promoting new studies on specific fields of knowledge and less-explored areas of Italy; (c) testing new approaches to evaluate seismic potential; (d) bounding slip rate values to use within probabilistic hazard estimates; and (e) preparing the way towards a future seismic hazard map of Italy. It was designed with three scientific parts – nationwide basic data, rheology, and field studies – and implemented into four tasks: 1) earthquake geodesy and modeling, 2) seismological data and earthquake statistics, 3) earthquake geology, and 4) tsunamis. Although with many difficulties and some delay, described in the appropriate section, all the above objectives have generally been accomplished. New observations were collected through original fieldwork and more sophisticated analyses were performed on existing data. Datasets needed for the seismic hazard estimates were updated at various levels by reducing both epistemic and aleatory uncertainties. New studies were carried out on specific fields of knowledge, e.g. addressing the repeatability of geodetic and stress data measurements or the seismogenic behavior of misoriented faults. Studies on less-explored areas were stimulated, and faults, whose seismic potential was not previously accounted for, were mapped and/or parameterized in the Ionian and Adriatic Seas, in Calabria, Sicily and the Southwestern Alps. Independent approaches to evaluate the seismic potential were tested, and a large effort toward homogenization and verifiability was made. The substantial improvements of nationwide datasets and understanding of the tectonic processes in large areas of the country set the basis for a significantly better assessment of seismic hazard. 2010-06-29T22:00:00Z http://hdl.handle.net/2122/7454 Title: Rupture speed and slip velocity: What can we learn from simulated earthquakes? Authors: Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: In this paper we consider a wide catalog of synthetic earthquakes, numerically modeled as spontaneous, fully 22 dynamic, 3-D ruptures on extended faults, governed by different friction laws, including slip-dependent and 23 rate- and state-dependent equations.We analyze the spatial correlations between the peak of fault slip velocity 24 (vpeak) and the rupture speed (vr) at which the earthquake spreads over the fault.We found that vpeak positively 25 correlates with vr and that the increase of vpeak is roughly quadratic.We found that near the transition between 26 sub- and supershear regimes vpeak significantly diminishes and then starts to increase againwith the square of vr . 27 This holds for all the governing models we consider and for both homogeneous and heterogeneous configura- 28 tions. Moreover, we found that, on average, vpeak increases with the magnitude of the event (vpeak~M0 0.18). Our 29 results can be incorporated as constraints in the inverse modeling of faults. 2011-11-02T23:00:00Z http://hdl.handle.net/2122/6869 Title: Static stress drop as determined from geodetic strain rates and statistical seismicity Authors: Caporali, A.; Dipartimento di Geoscienze, Università di Padova, Italy.; Barba, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Carafa, M. M. C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Devoti, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Pietrantonio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Riguzzi, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: Two critical items in the energetic budget of a seismic province are the strain rate, which is measured geodetically on the Earth’s surface, and the yearly number of earthquakes exceeding a given magnitude. Our study is based on one of the most complete and recent seismic catalogs of Italian earthquakes and on the strain rate map implied by a multi-year velocity solution for permanent GPS stations. For 36 homogeneous seismic zones, we used the appropriate Gutenberg Richter relation based on the seismicity catalog to estimate a seismic strain rate, which is the strain rate associated with the mechanical work due to a co-seismic displacement. The volume storing most of the elastic energy is associated with the long-term deformation of each seismic zone, and therefore, the seismic strain rate is inversely proportional to the static stress drop. The GPS-derived strain rate for each seismic zone limits the corresponding seismic strain rate, and an upper bound for the average stress drop is estimated. These results demonstrated that the implied regional static stress drop ranged from 0.1 to 5.7 MPa for catalog earthquakes in the moment magnitude range [4.5–7.3]. These results for stress drop are independent of the “a” and “b” regional parameters and heat flow but are very sensitive to the assumed maximum magnitude of a seismic province. The data do not rule out the hypothesis that the stress drop positively correlates with the time elapsed after the largest earthquake recorded in each seismic zone. Description: Accepted for publication in Journal of Geophysical Researches. Copyright (2010) American Geophysical Union 2009-12-31T23:00:00Z http://hdl.handle.net/2122/6868 Title: Role of the brittle-ductile transition on fault activation Authors: Doglioni, C.; Dipartimento di Scienze della Terra, Università Sapienza, Roma, Italy; Barba, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Carminati, E.; Dipartimento di Scienze della Terra, Università Sapienza, Roma, Italy; Riguzzi, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: We model a fault cross-cutting the brittle upper crust and the ductile lower crust. In the brittle layer the fault is assumed to have stick-slip behaviour, whereas the lower ductile crust is inferred to deform in a steady-state shear. Therefore, the brittle-ductile transition (BDT) separates two layers with different strain rate and structural style. This contrasting behaviour determines a stress gradient at the BDT that is eventually dissipated during the earthquake. During the interseismic period, along a normal fault there should form a dilated hinge at and above the BDT. Conversely, an over-compressed volume should rather develop above a thrust plane at the BDT. On a normal fault the earthquake is associated with the coseismic closure of the dilated fractures generated in the stretched hangingwall during the interseismic period. In addition to the shear stress overcoming the friction of the fault, the brittle fault moves when the weight of the hangingwall exceeds the strength of the dilated band above the BDT. On a thrust fault, the seismic event is instead associated with the sudden dilation of the previously over-compressed volume in the hangingwall above the BDT, a mechanism requiring much more energy because it acts against gravity. In both casess, the deeper the BDT, the larger the involved volume, and the bigger the related magnitude. We tested two scenarios with two examples from L’Aquila 2009 (Italy) and Chi-Chi 1999 (Taiwan) events. GPS data, energy dissipation and strain rate analysis support these contrasting evolutions. Our model also predicts, consistently with data, that the interseismic strain rate is lower along the fault segment more prone to seismic activation. 2009-12-31T23:00:00Z http://hdl.handle.net/2122/6867 Title: Determining rheology from deformation data: The case of central Italy Authors: Carafa, M. M. C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Barba, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: The study of geodynamics relies on an understanding of the strength of the lithosphere. However, our knowledge of kilometer-scale rheology has generally been obtained from centimeter-sized laboratory samples or from microstructural studies of naturally deformed rocks. In this study, we present a method that allows rheological examination at a larger scale. Utilizing forward numerical modeling, we simulated lithospheric deformation as a function of heat flow and rheological parameters and computed several testable predictions including horizontal velocities, stress directions, and the tectonic regime. To select the best solutions, we compared the model predictions with experimental data. We applied this method in Italy and found that the rheology shows significant variations at small distances. The strength ranged from 0.60.2 TN/m within the Apennines belt to 216 TN/m in the external Adriatic thrust. These strength values correspond to an aseismic mantle in the upper plate and to a strong mantle within the Adriatic lithosphere, respectively. With respect to the internal thrust, we found that strike-slip or transpressive, but not compressive, earthquakes can occur along the deeper portion of the thrust. The differences in the lithospheric strength are greater than our estimated uncertainties and occur across the Adriatic subduction margin. Using the proposed method, the lithospheric strength can be also determined when information at depth is scarce but sufficient surface data are available. Description: Accepted for publication in Tectonics. Copyright (2010) American Geophysical Union 2009-12-31T23:00:00Z http://hdl.handle.net/2122/6753 Title: Introduction: LASI III—Magma pulses and sheets in tabular intrusions Authors: Rocchi, S.; Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy; Dini, A.; Istituto di Geoscienze e Georisorse, CNR Pisa, Pisa, Italy; Mazzarini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Westerman, D. S.; Department of Geology, Norwich University, Northfield, Vermont, USA Abstract: The origins of granites and intrusive rocks have been widely discussed for a couple of centuries, and the way volcanoes work and their magma forms have attracted scientists, naturalists, and laymen since the dawn of humankind. However, shallow igneous intrusions, representing the obvious link between the hidden kingdom of Pluto and the fiery realm of Vulcanus, have been partly overlooked, leading to some lack of communication between “plutonic” and “volcanic” researchers. An effort devoted to heal this breach has been contributed to by the establishment of the LASI conferences (named after laccolith and sill, the main types of shallow igneous intrusions). 2010-05-31T22:00:00Z http://hdl.handle.net/2122/6710 Title: Relations between deformation and upper crustal magma emplacement in laboratory physical models Authors: 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 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. 2010-03-18T23:00:00Z http://hdl.handle.net/2122/6646 Title: Thermal enhancement of radon emission from geological materials. Implications for laboratory experiments on rocksunder increasing deformation Authors: Tuccimei, P.; Univ. Roma3, Italy; Castelluccio, M.; Univ. Roma3, Italy; Moretti, S.; Univ. Roma3, Italy; Mollo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Scarlato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Editors: Veress, B.; //; Szigethy, J.; // Abstract: Radon gas is the subject of a great deal of research because its concentration builds up into indoor air and the long-term radon exposure is considered the second cause of lung cancer, after smoking. In addition to that, the release of radon from soil is under investigation in active volcanic and seismic areas because radon anomalies are believed to occur before earthquakes and volcanic eruptions. Several papers report results of laboratory experiments on the effects of activity concentration of 222Rn and 220Rn precursors, humidity content and grain size of geological materials over the radon emission. However no correspondent studies have targeted the effect of the temperature on radon release. The present contribution focuses on the influence of temperature, varying from 20 to 60 °C, on 222Rn and 220Rn emission from two volcanic rocks, a tuff and a lava flow. The experimental apparatus consists of a small accumulation chamber coupled to solid-state alpha spectroscopy; it also allows to keep constant the experimental temperatures applied to the rock sample. The effect of ambient temperature on detection efficiency is also investigated. Results show a significant enhancement of radon emissions from rocks with increasing temperature. The results of these experiments suggest that thermal enhancement of radon emission can be used to investigate more precisely the correlation between physical mechanisms determining damage in stressed rocks and radon release, taking advantage of the improved radon emission. Experimental test with a better resolution are the key to interpret radon anomalies preceding earthquakes or volcanic eruption. 2010-12-31T23:00:00Z http://hdl.handle.net/2122/6313 Title: Seismic attenuation and mantle wedge temperature in the northern Apennine subtuction zone (Italy) from teleseismic body wave spectra. Authors: Piccinini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Di Bona, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Lucente, F. P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Levin, V.; Rutgers University; Park, J.; Yale University Abstract: We analyze P and S wave spectra from moderate‐ to deep‐focus teleseisms recorded at the Retreating‐Trench, Extension, and Accretion Tectonics (RETREAT) temporary broadband seismic network to assess the variations of the Earth mantle attenuation in the northern Apennines region (Italy). For each earthquake, we compute the ratio between the spectrum at each station and the average spectrum, in order to estimate t* residuals (Δt*) from the spectral ratio decay. The number and distribution of the teleseisms useable for the P wave t* calculation allow for a gross azimuthal analysis; although the (Δt*) values at single station display, in most cases, azimuthal‐dependent fluctuations, their overall distribution shows a partition of the study region into two main areas, whose gross features remain almost unchanged over the whole azimuthal range. This partition is confirmed by the S wave t* mean values, computed for each station over the set of useable events. We distinguish a relatively high attenuation area on the western, Tyrrhenian side and a relatively low attenuation area on the eastern, Adriatic side. By correlating our Δt* estimates and the velocity structure derived from the existing tomographic models, we compute the ranges of possible P and S wave Q values in the mantle wedge above the Apennines slab (on the Tyrrhenian side) and in the asthenosphere below the Adriatic region. Furthermore, the determined attenuation properties are used to draw some inferences on the thermal state of the uppermost mantle and on the physical properties of the tectonic elements, which constitute the subduction system in the region. Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union. 2010-09-13T22:00:00Z http://hdl.handle.net/2122/6080 Title: Eruptive versus non-eruptive behaviour of large calderas: the example of Campi Flegrei caldera (southern Italy) Authors: Carlino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Somma, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia Abstract: Caldera eruptions are among the most hazardous of natural phenomena. Many calderas around the world are active and are characterised by recurrent uplift and subsidence periods due to the dynamics of their magma reservoirs. These periods of unrest are, in some cases, accompanied by eruptions. At Campi Flegrei caldera (CFc), which is an area characterised by very high volcanic risk, the recurrence of this behaviour has stimulated the study of the rock rheology around the magma chamber, in order to estimate the likelihood of an eruption. This study considers different scenarios of shallow crustal behaviour, taking into account the earlier models of CFc ground deformation and caldera eruptions, and including recent geophysical investigations of the area. A semi-quantitative evaluation of the different factors that lead to magma storage or to its eruption (such as magma chamber size, wall-rock viscosity, temperature, and regional tectonic strain rate) is reported here for elastic and viscoelastic conditions. Considering the large magmatic sources of the CFc ignimbrite eruptions (400–2,000 km3) and a wall-rock viscosity between 1018 and 1020 Pa s, the conditions for eruptive failure are difficult to attain. Smaller source dimensions (a few cubic kilometres) promote the condition for fracture (eruption) rather than for the flow of wall rock. We also analyse the influence of the regional extensional stress regime on magma storage and eruptions, and the thermal stress as a possible source of caldera uplift. The present study also emphasises the difficulty of distinguishing eruption and non-eruption scenarios at CFc, since an unambiguous model that accounts for the rock rheology, magma-source dimensions and locations and regional stress field influences is still lacking. 2009-12-31T23:00:00Z