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51.
Rosalba Napoli Gilda Currenti Ciro Del Negro Agnese Di Stefano Filippo Greco Enzo Boschi 《Bulletin of Volcanology》2011,73(9):1311-1322
Significant changes in the local magnetic field marked the resumption of eruptive activity at Stromboli volcano on February
27, 2007. After differential magnetic fields were obtained by filtering out external noise using adaptive filters and seasonal
thermal noise using temperature data, we identified step-like changes of 1–4 nT coincident with the opening of eruptive fissures
in the upper part of the Sciara del Fuoco. The magnetic variations detected at two stations are closely related to the propagation
of a shallow NE–SW magmatic intrusion extending beyond the summit craters area. These observations are consistent with those
calculated using piezomagnetic models in which stress-induced changes in rock magnetization are produced by the magmatic intrusion.
No significant magnetic changes were observed when the first fractures opened along the NE crater rim. Indeed, the stress-induced
magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and/or thermal
state of the summit area. The continuous long-term decay characterizing the post-eruptive magnetic pattern can be related
to a time-dependent relaxation process. A Maxwell rheology was assumed and the temporal evolution of the piezomagnetic field
was evaluated. This allowed us to estimate the rheological properties of the medium; in particular, an average viscosity ranging
between 1016 and 1017 Pa⋅s was a relaxation time τ of about 38 days. 相似文献
52.
Paul Eccleston Bruce Swinyard Marcel Tessenyi Giovanna Tinetti Ingo Waldmann Marc Ferlet Ranah Irshad Tanya Lim Kevin Middleton Tom Bradshaw Martin Crook Tom Hunt Berend Winter Ian Bryson Naidu Bezawada William Taylor Neil Bowles Enzo Pascale Gianluca Morgante Emanuele Pace Alberto Adriani Jean-Michel Reess Marc Ollivier Roland Ottensamer Mirek Rataj Gonzalo Ramos Zapata Jan-Rutger Schrader Avri Selig Kate Isaak Martin Linder Ludovic Puig 《Experimental Astronomy》2015,40(2-3):427-447
53.
Saleem Zaroubi Enzo Branchini 《Monthly notices of the Royal Astronomical Society》2005,357(2):527-534
We introduce a simple linear equation relating the line-of-sight peculiar-velocity and density contrast correlation functions. The relation, which we call the Gaussian cell two-point 'energy-like' equation , is valid at the distant-observer limit and requires Gaussian smoothed fields. In the variance case, i.e. at zero lag, the equation is similar in its mathematical form to the Irvine–Layzer cosmic energy equation. β estimation with this equation from the Point Source Catalogue Redshift (PSC) survey and the SEcat catalogue of peculiar velocities is carried out, returning a value of β= 0.44 ± 0.08 . The applicability of the method for the 6dF galaxy redshift and peculiar motions survey is demonstrated with mock data where it is shown that β could be determined with ≈10 per cent accuracy. The prospects for constraining the dark energy equation of state with this method from the kinematic and thermal Sunyaev–Zel'dovich cluster surveys are discussed. The equation is also used to construct a non-parametric mass-density power-spectrum estimator from peculiar-velocity data. 相似文献
54.
Adi Nusser Luiz N. da Costa Enzo Branchini Mariangela Bernardi M.V. Alonso Gary Wegner C. N. A. Willmer P. S. Pellegrini 《Monthly notices of the Royal Astronomical Society》2001,320(3):L21-L24
We present a comparison between the peculiar velocity field measured from the ENEAR all-sky D n – σ catalogue and that derived from the galaxy distribution of the IRAS Point Source Catalog Redshift Survey (PSC z ). The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500 km s−1 at 3000 km s−1 . The general flow patterns in the filtered ENEAR and PSC z velocity fields agree well within 6000 km s−1 , assuming a linear biasing relation between the mass and the PSC z galaxies. The comparison allows us to determine the parameter where Ω is the cosmological density parameter and b is the linear biasing factor. A likelihood analysis of the ENEAR and PSC z modes yields in good agreement with values obtained from Tully–Fisher surveys. 相似文献
55.
56.
In the present study, the dissolution and mobilization of Ce introduced in a simulated nuclear waste glass (MW) as a surrogate of Pu was investigated after leaching in pure water over 12 a at 90 °C and pH ∼ 9.6. The microscopic distribution and oxidation state of Ce in the altered glass were studied using micro-X-ray fluorescence (micro-XRF) mapping techniques and micro-X-ray near-edge absorption spectroscopy (micro-XANES). Distribution maps of CeIII and CeIV were obtained by recording the Lα fluorescence emission at two different incident X-ray energies, coinciding with the maximum contrast between CeIII and CeIV fluorescence intensities. The micro-XRF maps revealed that Ce was dominantly present as oxidized species (CeIV) in the original glass. After dissolution from the glass matrix, CeIV was partly reduced and re-immobilized as CeIII at grain boundaries or in the interstitial spaces between the glass particles. The concentration of CeIII was found to correlate with the spatial distribution of secondary Mg-clay formed during the aqueous corrosion as the main glass alteration product. Micro-XANES spectra collected at locations representative of both altered and non-altered glass domains confirmed the findings obtained by the redox mapping. Because redox-sensitive elements in the pristine MW glass (Fe, Cr, Se) occur almost exclusively as oxidized species, reduction of CeIV was probably mediated by an external source of reductants, such as Fe(0) from the steel reaction vessel. 相似文献
57.
During three years preceding the 1976 Friuli earthquake, a continuous southward ground tilt was recorded by a tiltmeter placed near Tolmezzo, 15 km north-west of the epicentre of the impending earthquake. The cumulative ground tilt amounted to as much as 3 minutes of arc. Since the tiltmeter was placed in the proximity of an active fault, such a tilt can be explained if the fault slipped aseismically on its shallower section during the same three year period. Aseismic slip on the fault might have been caused by the same mechanism which concentrated stress in the region and eventually produced the 1976 earthquake. 相似文献
58.
Michele Dragoni Maurizio Bonafede Enzo Boschi 《Journal of Volcanology and Geothermal Research》1986,30(3-4)
It is widely recognized that lavas behave as Bingham liquids, which are characterized by a yield stress σ and a plastic viscosity η. We consider two models describing downslope flows of a Bingham liquid with different aspect ratios A (= flow height/flow width): model 1 with A 1 and model 2 with A ≈ 1. Sufficiently uphill with respect to the front, such flows can be considered as laminar and locally isothermal. For both models, we obtain analytically the steady-state solution of the Navier-Stokes equations and the constitutive equation for a Bingham liquid. We study the flow height and velocity as functions of flow rate, rheological parameters and ground slope. It is found that such flows remain in the Newtonian regime at low yield stresses (σ 103dyne/cm2), but the transition to the Bingham regime also depends on flow rate and occurs at higher values of σ for higher flow rates: for instance, a high aspect ratio flow (model 2) is still very close to the Newtonian regime at σ = 104 dyne/cm2, if the flow rate is greater than 105 g/s. In the Bingham regime, flow heights are generally greater and flow velocities are smaller than in the Newtonian regime; moreover, flow heights are independent of flow rate, so that a change in flow rate results exclusively in a velocity change. After assuming a specific temperature dependence of σ and η between the solidus and the liquidus temperatures of an ideal Bingham liquid (1000°C and 1200 °C respectively), flow heights and velocities are examined as functions of temperature along the flow. Several effects observed in lava flows are predicted by these models and allow a more quantitative insight into the behaviour of lava flows. 相似文献
59.
The purpose of this work is to evaluate under what conditions it is feasible and with what accuracy it is possible to locate the nucleation point of a large earthquake, given the availability of aftershocks located with high precision by the deployment of a local network. We experiment with several approaches and apply them lo the location of the epicentre of the 1980 November 23 Irpinia earthquake ( M w = 6.9).
First we use local Pg phases selected to optimize the azimuthal coverage, obtaining a well-constrained location with a small statistical error, which typically underestimates the true hypocentre uncertainty.
We then exploit the relative location technique, obtaining stable, almost coincident solutions under three conditions: (1) using multiple independent master events to derive an average epicentre; (2) fitting simultaneously the larger data set for all available master events, using a forward approach; (3) conducting an a priori evaluation of the statistics of station and master events to separate model uncertainties and improve the statistical accuracy of the relative locations. Moreover, only by introducing station statistics can we achieve the desired accuracy of ≅ 1 km in constraining the rupture nucleation point of this large earthquake, and we show that the application of the relative location technique to uncleaned, unweighted data for a single master event provides only a crude epicentre with a confidence ellipse deceivingly smaller than the true hypocentre uncertainty.
The revised epicentre for the 1980 November 23 Irpinia earthquake (48.803 °N-15.302°E) validates the class of multidisciplinary reconstructions of the source process such as the model of Valensise et al. (1989), based on the hypocentre of Westaway & Jackson (1987), and is shifted by almost 13 km to the NW of the epicentre recently proposed by Westaway (1992). 相似文献
First we use local P
We then exploit the relative location technique, obtaining stable, almost coincident solutions under three conditions: (1) using multiple independent master events to derive an average epicentre; (2) fitting simultaneously the larger data set for all available master events, using a forward approach; (3) conducting an a priori evaluation of the statistics of station and master events to separate model uncertainties and improve the statistical accuracy of the relative locations. Moreover, only by introducing station statistics can we achieve the desired accuracy of ≅ 1 km in constraining the rupture nucleation point of this large earthquake, and we show that the application of the relative location technique to uncleaned, unweighted data for a single master event provides only a crude epicentre with a confidence ellipse deceivingly smaller than the true hypocentre uncertainty.
The revised epicentre for the 1980 November 23 Irpinia earthquake (48.803 °N-15.302°E) validates the class of multidisciplinary reconstructions of the source process such as the model of Valensise et al. (1989), based on the hypocentre of Westaway & Jackson (1987), and is shifted by almost 13 km to the NW of the epicentre recently proposed by Westaway (1992). 相似文献
60.
Antonella Longo Paolo Papale Melissa Vassalli Gilberto Saccorotti Chiara P. Montagna Andrea Cassioli Salvatore Giudice Enzo Boschi 《Bulletin of Volcanology》2012,74(4):873-880
Many volcanic eruptions are shortly preceded by injection of new magma into a pre-existing, shallow (<10 km) magma chamber,
causing convection and mixing between the incoming and resident magmas. These processes may trigger dyke propagation and further
magma rise, inducing long-term (days to months) volcano deformation, seismic swarms, gravity anomalies, and changes in the
composition of volcanic plumes and fumaroles, eventually culminating in an eruption. Although new magma injection into shallow
magma chambers can lead to hazardous event, such injection is still not systematically detected and recognized. Here, we present
the results of numerical simulations of magma convection and mixing in geometrically complex magmatic systems, and describe
the multiparametric dynamics associated with buoyant magma injection. Our results reveal unexpected pressure trends and pressure
oscillations in the Ultra-Long-Period (ULP) range of minutes, related to the generation of discrete plumes of rising magma.
Very long pressure oscillation wavelengths translate into comparably ULP ground displacements with amplitudes of order 10−4–10−2 m. Thus, new magma injection into magma chambers beneath volcanoes can be revealed by ULP ground displacement measured at
the surface. 相似文献