http://hdl.handle.net/2122/255 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/6079 Titolo: Array analysis and precise source location of deep tremor in Cascadia<br/><br/>Autori: La Rocca, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Galluzzo, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Malone, S.; Department of Earth and Space Sciences, University of Washington, USA; McCausland, W.; Cascade Volcano Observatory, U.S. Geological Survey, Vancouver, USA; Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia<br/><br/>Abstract: We describe a new method to estimate the S‐P time of tremor‐like signals and itsapplication to the nonvolcanic tremor recorded in July 2004 by three dense arrays inCascadia. The cross correlation between vertical and horizontal components indicates thatvery often the high‐amplitude tremor signal contains sequences of P and S wavescharacterized by constant S‐P times (TS‐P) in the range 3.5–7 s. A detailed observation ofthe three component seismograms stacked over the array stations confirms the presence ofP and S wave sequences. The knowledge of the TS‐P poses a strong constrain on thesource‐array distance, which dramatically reduces the uncertainty on source locationswhen used with more traditional array processing techniques. Data were analyzed usingthe zero lag cross‐correlation technique (ZLCC) to estimate the propagation propertiesof the most correlated phases in the wavefield. Detailed polarization analyses werecomputed using the covariance matrix method in the time domain. Polarization parameters,joint with the results of ZLCC, allows for the discrimination between P and S coherentwaves. Results show that the tremor wavefield is composed mostly by shear waves,although a consistent amount of coherent P waves is often observable. The comparison ofthe back azimuth at the three arrays indicate that the source of deep tremor migrates over awide area, and often many independent sources located far from each other are active atthe same time. The tremor source was located by a probabilistic method that uses theresults of ZLCC, given a velocity model. When available, the inclusion of the TS‐P time inthe location procedure strongly reduces the depth range, with a distribution of hypocentersvery near the subduction interface. This result, significantly different compared withprevious less precise locations, makes the Cascadia nonvolcanic tremor more similar to thenonvolcanic tremor recorded in Japan, at least in cases of measurable TS‐P. Thepolarization azimuth aligned with the slow slip direction and the source located on theplate interface indicate that deep tremor and slow slip are two different manifestations of acommon phenomenon related with the subduction dynamics. Sat, 05 Jun 2010 00:00:00 GMT http://hdl.handle.net/2122/6021 Titolo: Array measurements of deep tremor signals in the Cascadia subduction zone<br/><br/>Autori: La Rocca, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; McCausland, W.; University of Washington, Seattle, USA; Galluzzo, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Malone, S.; University of Washington, Seattle, USA; Saccorotti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia<br/><br/>Abstract: Preliminary analysis of deep tremor recorded during July, 2004, in the Cascadia Subduction zone shows that the use of small aperture arrays can resolve the slowness and back azimuth of seismic waves with a useful resolution. Data were collected by three dense arrays of short-period seismometers specifically deployed in the Puget Sound area under an US-Italy-Canada cooperative effort. Slowness analyses at the three arrays indicate that the 2-4 Hz tremor wave-field is composed by waves propagating with apparent velocities higher than 4 km/s. Combining this with polarisation analysis show these waves to be transverse (SH) waves. However, P-waves, though smaller in amplitude, can be detected by different slowness values obtained for the radial and transverse components. The intersection of wave vectors determined by the back azimuth and slowness values measured at the three arrays provides a preliminary estimate of source location for a sample of the recorded deep tremor. Tue, 15 Nov 2005 00:00:00 GMT http://hdl.handle.net/2122/5879 Titolo: Roberto Mantovani (1854-1933) and his ideas on the expanding Earth, as revealed by his correspondence and manuscripts<br/><br/>Autori: Scalera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: Roberto Mantovani (Parma, 25 March 1854-Paris, 10 January 1933) – a musician and geologist trained in theDuchy of Parma – was a Consul in the French island of La Réunion at the end of the nineteenth century. In 1878drawing general conclusions from the similarity in shape between the facing banks of a river that flowed in a volcanicfracture, and the way in which the layers corresponded, Mantovani formulated a mobilistic theory, attributingthe moving apart of the continents to the expansion of the entire planet. This theory is more general than thatof Wegener from the first decades of the following century. Mantovani’s hypothesis was officially recognised bythe French Geological Society in 1924, which incorporated it in its body of legitimate ideas. Encouraged by Bourcartin 1924, Wegener quoted the Italian in his famous book as one who offered ideas extraordinarily close to hisown. A letter of Mantovani to Wegener, and the sceptical answer of the German scientist, have been recentlyfound. In his letter Mantovani shows a greater awareness of the predecessors of the continental drift than Wegenerhimself. Mantovani continued to disseminate his idea up to the last years of his life. A final pamphlet, of 1930,was printed with this dedication: «to the mathematicians, physicists, astronomers, geologists, and anyone interestedin the great enigmas of the Universe». His biography has been reconstructed thanks to the correspondencescarefully conserved in the archives of the Italian Ministry of Foreign Affairs, the Ethnographic Museum Luigi Pigorini,the Società Geografica Italiana, and in the private files of his direct descendants.<br/><br/>Descrizione: Biografia di un antesignano della espansione dei fondali oceanici e della Terra. Tue, 01 Dec 2009 00:00:00 GMT http://hdl.handle.net/2122/5709 Titolo: Active strain-rate Across the Messina Straits and Kinematics of Sicily and Calabria From GPS Data<br/><br/>Autori: mastrolembo ventura, brunella; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; serpelloni, enrico; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; burgmann, roland; Department of Earth and Planetary Science, University of California, Berkeley, USA.; anzidei, marco; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; baldi, paolo; Dipartimento di Fisica, Università degli Studi di Bologna, Italy.; cavaliere, adriano; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia<br/><br/>Curatori: European Geoscience Union<br/><br/>Abstract: The Messina Straits is the locus of one of the strongest seismic event that ever hit Italy during historical times, the 1908 Mw 7.1 earthquake, and the same region also suffered major damage from other strong earthquakes in the last few centuries. However, despite the large amount of data and studies carried out, our knowledge of the present-day deformation of this area is still debated. While a general consensus has been reached about the kinematics of the 1908 causative fault, less is known about the rate and shape of interseismic loading across the Straits, and debate continues also about the general kinematics and geodynamic framework of this region which are strongly influenced by subduction and retreat of Ionian lithosphere. Thanks to the increasing number of GPS Networks in the study region it is now possible to study both the regional kinematics and strain loading across active faults. In this work we analyze all the observations collected over the Messina non-permanent GPS Network for the 1994-2008 time span, and data from about 600 CGPS stations in the Euro-Mediterranean region, using the GAMIT software. The output of our analysis is a new and denser velocity field, which is used to study the plate kinematics and the rate of interseismic strain building across the Straits. GPS velocities show a sudden change in their orientation across the Straits moving to NNW-ward, in Estern Sicily, to NNE-ward in Western Calabria, depicting this area as a primary boundary between two different tectonic domains. The maximum strain-rates observed across the Straits are about 120 nanostrain/yr, with extension oriented about normal to the coasts of Sicily according to the presence of a normal fault. The measured velocity gradient can be used to model the creeping dislocation at depth, however, over the Messina Straits the interseismic elastic strains accumulating across other nearby active faults can significantly affect the observed velocity gradient.For this reason we investigate, using a regional elastic block-modeling approach, these effects. We use the block model to test for different microplates configurations and to account for nearby active faults while inverting for optimal fault geometry and intersismic slip-rates across the Straits. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/2122/5371 Titolo: Cascadia Tremor Located Near Plate Interface Constrained by S Minus P Wave Times<br/><br/>Autori: La Rocca, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Creager, K. C.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA.; Galluzzo, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Malone, S.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA.; Vidale, J. E.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA.; Sweet, R.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA.; Wech, G.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA.<br/><br/>Abstract: Nonvolcanic tremor is difficult to locate because it does not produce impulsive phases identifiableacross a seismic network. An alternative approach to identifying specific phases is to measurethe lag between the S and P waves. We cross-correlate vertical and horizontal seismograms toreveal signals common to both, but with the horizontal delayed with respect to the vertical. Thislagged correlation represents the time interval between vertical compressional waves andhorizontal shear waves. Measurements of this interval, combined with location techniques, resolvethe depth of tremor sources within T2 kilometers. For recent Cascadia tremor, the sourceslocate near or on the subducting slab interface. Strong correlations and steady S-P time differencesimply that tremor consists of radiation from repeating sources. Fri, 30 Jan 2009 00:00:00 GMT http://hdl.handle.net/2122/5230 Titolo: Seismic moment tensors of the April 2009, L’Aquila (Central Italy),<br/><br/>Autori: Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Salimbeni, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Ekström, G.; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA; Olivieri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia<br/><br/>Abstract: On 2009 April 6, the Central Apennines were hit by an Mw = 6.3 earthquake. The region had been shaken since 2008 October by seismic activity that culminated in two foreshocks with Mw > 4, 1 week and a few hours before the main shock. We computed seismic moment tensors for 26 events with Mw between 3.9 and 6.3, using the Regional Centroid Moment Tensor (RCMT) scheme. Most of these source parameters have been computed within 1 hr after the earthquake and rapidly revised successively. The focal mechanisms are all extensional, with a variable and sometimes significant strike-slip component. This geometry agrees with the NE–SW extensional deformation of the Apennines, known from previous seismic andgeodetic observations. Events group into three clusters. Those located in the southern area have larger centroid depths and a wider distribution of T-axis directions. These differences suggest that towards south a different fault systemwas activated with respect to the SW-dippingnormal faults beneath L’Aquila and more to the north. Sun, 15 Nov 2009 00:00:00 GMT http://hdl.handle.net/2122/5210 Titolo: DISS3 TUTORIAL SERIES: GUIDELINES FOR COMPILING RECORDS OF THE DATABASE OF INDIVIDUAL SEISMOGENIC SOURCES, VERSION 3<br/><br/>Autori: Basili, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Kastelic, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Valensise, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; DISS, Working Group 2009; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: This document illustrates in details the raw structure of the Database of Individual Seismogenic Sources, version 3 [Basili et al., 2008; http://diss.rm.ingv.it/diss/] - hereinafter referred to as the Database –and is dedicated at instructing any potential contributor, outside the DISS Working Group, on how to populate it with new seismogenic sources. It is worth of notice that the primary purpose of the Database is toprovide a seismogenic source model at regional scale. It is hence usually populated by filling in large regions at once, not record by record. Tue, 01 Sep 2009 00:00:00 GMT http://hdl.handle.net/2122/5124 Titolo: new concept in global tectonics<br/><br/>Autori: bozic, zeljko; none<br/><br/>Abstract: Nowdays we can easily take for a fact the existance of ancient supercontinent named Pangea.If one just takes a glance at borderlines of modern continents one can conclude,without further argument,that they were once conjoined indeed.But the process of development and the process of disintegration of Pangea still inflames bitter arguments.New concept in global tectonics endorses two-layered lithosphere: Primary Layer: One that covers all of the Earths surface,and Secondary Layer: One that exists on top of Primery layer and consists of Earths continents (originated as Pangea). Therefor,covering aproximetly one quarter of Earths surface. Wed, 01 Jul 2009 00:00:00 GMT http://hdl.handle.net/2122/5049 Titolo: Deep geometry and rheology of an orogenic wedge developing above a continental subduction zone: Seismological evidence from the northern-central Apennines (Italy)<br/><br/>Autori: 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; Speranza, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: Data from high-density seismic networks deployed between 2000 and 2007 in the north-central Apennines (Italy) yield unprecedentedimages of an active orogenic wedge. Earthquake foci from the northern Apennines define a Benioff zone deepening westward from theAdriatic foreland down to ~60 km depth below the chain. The seismicity shows that only the lowermost ~10 km of the Adriatic forelandcrust is subducted, whereas the uppermost ~20 km is incorporated into the orogenic wedge. Farther west, an aseismic mantle with markedlynegative P-wave-velocity (Vp) anomalies is interpreted as asthenosphere flowing toward an Adriatic slab in retrograde motion. Threecrustal layers with different Vp and seismicity characteristics are imaged below the northern Apennines: an uppermost 10-km-thick fastlayer affected by extensional faulting, a slow layer with diffuse seismicity down to ~15 km depth, and a lowermost fast and aseismic layerresting directly above the asthenosphere. We interpret the latter layer as having formed by anhydrous crust undergoing granulitization,whereas trapped CO2 (either from the underlying granulites or from the subducting Adriatic crust) is inferred to have been responsiblefor both low Vp and diffuse seismicity in the middle crust. Trapped CO2 is released along the easternmost normal fault systems breakingthe Apennine upper crust, consistent with geochemical and seismotectonic evidence. Compressive earthquakes at 20–25 km depth alongthe external front suggest offscraping of the subducting foreland crust and show that asthenospheric flow represents the primary sourceof ongoing shortening along the belt front. Wed, 01 Apr 2009 00:00:00 GMT http://hdl.handle.net/2122/5038 Titolo: Structural features of Panarea volcano in the frame of the Aeolian Arc (Italy): Implications for the 2002–2003 unrest<br/><br/>Autori: Acocella, V.; Dip. Sc. Geologiche Roma Tre. L.S.L. Murialdo 1, 00146 Roma, Italy; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Walter, T. R.; Deutsches GeoForschungsZentrum (GFZ) Potsdam, Dept. Physics of the Earth, Telegrafenberg, 14473 Potsdam, Germany<br/><br/>Abstract: Panarea, characterized by gas unrest in 2002–2003, is the volcanic island with the least constrainedstructure in the eastern-central Aeolian Arc (Italy). Based on structural measurements, we define here itsdeformation pattern relative to the Arc. The main deformations are subvertical extension fractures (63%of data), normal faults (25%) and dikes (12%). The mean orientation of the extension fractures and faultsis ∼N38◦E, with a mean opening direction of N135◦ ±8◦, implying extension with a moderate componentof dextral shear. These data, matched with those available for Stromboli volcano (pure opening) andVulcano, Lipari and Salina volcanoes (predominant dextralmotions) along the eastern-central Arc, suggesta progressivewestward rotation of the extension direction and an increase in the dextral shear. The dextralshear turns into compression in the western arc. The recent unrest at Panarea, coeval to that of nearbyStromboli, may also be explained by the structural context, as both volcanoes lie along the portion of theArc subject to extension. Fri, 01 May 2009 00:00:00 GMT