131 research outputs found
Post-seismic stress relaxation with a linear transient rheology
We performed an analysis of post-seismic stress relaxation, taking into account generalized linear rheologies. We compared the stress field (and its derived functions) obtained with a classical Maxwell rheology with that obtained with a transient Burgers body. From a set of synthetic case studies, we have revealed quantitative and qualitative differences both in relaxation times and in local stress values when a transient rheology is introduced. As a practical application, we modeled the time evolution of the Coulomb failure function following the 2009 L'Aquila earthquake, and we show that a transient rheology can lead to non-monotonic time dependence
3D Finite Element Modeling of the 2009 L'Aquila Earthquake Deformation Field
The L'Aquila earthquake (Mw 6.3) occurred on April 6th at 01:32 UTC in the Central Appennines at a depth of about 9 km and was felt all over Central Italy. The main shock was preceded by a long seismic sequence started several months before and was followed by thousands of aftershocks, some of them with Mw>4.
We built up a high resolution three-dimensional model, incorporating surface topography, which was discretized using 20-nodes brick elements. The element horizontal size is biased from 500 m to 2 km using the paving meshing algorithm in combination with an appropriate adaptive sizing function. A realistic rheology was introduced from a vp/vpvs travel time tomographic model.
We computed the co-seismic deformation induced by the earthquake by means of a recently developed finite elements simulation tool, FEMSA (Finite Element Modeling for Seismic Applications). We used different seismic source models obtained from fault inversion of GPS measurements, joint inversion of strong motion and GPS data and from inversion of DInSAR displacements. The synthetic deformation patterns were compared with the experimental results in order to evaluate which source model better reconciles the data and quantify the trade off introduced by 1D simulations
Transient deformations in the Suez-Sinai area from GPS observations
We analyze data from four GPS campaigns carried out between 1997 and 2002 on
a network of 11 sites in the Suez-Sinai, the area of collision between the
African and the Arabian plates. This is the key area to understand how and in
which way Sinai behaves like a sub-plate of the African plate and the role
played between seismic and geodetic (long term) deformation release. Our
analysis shows that, on average, the Suez-Sinai area motion (in terms of ITRF00
velocities) matches African plate motion (NNR-NUVEL-1A model). However, the
baseline length variations show transient deformations in Sinai and across the
Gulf of Suez, reaching up a maximum value of about 1.5 cm in five years. Since
current geodynamical models do not predict significant tectonic deformation in
this area, we worked under the hypothesis that a contribute may be due to
post-seismic relaxation. Under this hypothesis, we compared the baselines
length variations with the post-seismic relaxation field associated with five
major local earthquakes occurred in the area, testing two different
viscoelastic models. Our results show that the transient deformations are
better modelled for viscosity values of 1018 Pa s in the lower crust and 1020
Pa s in the asthenosphere. However, since the modelled post-seismic effect
results modest and a certain amount of the detected deformation is not
accounted for, we think that an improved modelling should take into account the
lateral heterogeneities of crust and upper mantle structures
Spacetime Hall-MHD turbulence at sub-ion scales: structures or waves?
Spatiotemporal properties of two-dimensional (2D) Hall-magnetohydrodynamic
turbulence at intermediate plasma are studied by means of Fast
Iterative Filtering, a new technique for the decomposition of nonstationary
nonlinear signals. Results show that the magnetic energy at sub-ion scales is
concentrated in perturbations with frequencies smaller than the ion-cyclotron
(IC) frequency and with polarization properties that are incompatible with both
kinetic Alfv\'en waves (KAWs) and IC waves. At higher frequencies, we clearly
identify signatures of both whistler waves and KAWs, however their energetic
contribution to the magnetic power spectrum is negligible. We conclude that the
dynamics of 2D Hall-MHD turbulence at sub-ion scales is mainly driven by
localized intermittent structures, with no significant contribution of wavelike
fluctuations.Comment: 10 pages, 5 figures. Accepted for publication on The Astrophysical
Journal Letter
Impact of Sumatra earthquake on CMB topography and core ellipticity
Characterization of the global impact of 2004 Sumatra earthquake event through the investigation of its effects on core-mantle boundary (CMB) shape and on the elliptical part of the gravity field (J2
Identification of the different magnetic field contributions during a geomagnetic storm in magnetospheric and ground observations
Abstract. We used the empirical mode decomposition (EMD) to investigate the time variation of the magnetospheric and ground-based observations of the Earth's magnetic field during both quiet and disturbed periods. We found two timescale variations in magnetospheric data which are associated with different magnetospheric current systems and the characteristic diurnal orbital variation, respectively. On the ground we identified three timescale variations related to the solar-wind–magnetosphere high-frequency interactions, the ionospheric processes, and the internal dynamics of the magnetosphere. This approach is able to identify the different physical processes involved in solar-wind–magnetosphere–ionosphere coupling. In addition, the large-timescale contribution can be used as a local index for the identification of the intensity of a geomagnetic storm on the ground
Modeling cardiac muscle fibers in ventricular and atrial electrophysiology simulations
Since myocardial fibers drive the electric signal propagation throughout the
myocardium, accurately modeling their arrangement is essential for simulating
heart electrophysiology (EP). Rule-Based-Methods (RBMs) represent a commonly
used strategy to include cardiac fibers in computational models. A particular
class of such methods is known as Laplace-Dirichlet-Rule-Based-Methods (LDRBMs)
since they rely on the solution of Laplace problems. In this work we provide a
unified framework, based on LDRBMs, for generating full heart muscle fibers.
First, we review existing ventricular LDRBMs providing a communal mathematical
description and introducing also some modeling improvements with respect to the
existing literature. We then carry out a systematic comparison of LDRBMs based
on meaningful biomarkers produced by numerical EP simulations. Next we propose,
for the first time, a LDRBM to be used for generating atrial fibers. The new
method, tested both on idealized and realistic atrial models, can be applied to
any arbitrary geometries. Finally, we present numerical results obtained in a
realistic whole heart where fibers are included for all the four chambers using
the discussed LDRBMs
Role of the external drivers in the occurrence of low-latitude ionospheric scintillation revealed by multi-scale analysis
We analyze the amplitude scintillation on L-band signals over San Miguel de Tucumán (Argentina), focusing on the multi-scale variability and speculating on the possible relationship between forcing factors from the geospace and the ionospheric response. The site is nominally located below the expected position of the southern crest of the Equatorial Ionospheric Anomaly (EIA). For this scope, we concentrate on the period 1?31 March 2011, during which one minor and one moderate storm characterize the first half of the month, while generally quiet conditions of the geospace stand for the second half. By leveraging on the Adaptive Local Iterative Filtering (ALIF) signal decomposition technique, weinvestigate the multi-scale properties of Global Navigation Satellite Systems (GNSS) amplitude scintillation and helio-geophysical parameters, looking for possible cause-effect mechanisms relating the former to the latter. Namely, we identify resonant modes in the Akasofu (e) parameter as likely related to the frequency components in the time evolution found for the amplitude scintillation index, hence modulating the scintillation itself.Fil: Spogli, Luca. Istituto Nazionale Di Geofisica E Vulcanologia, Rome; ItaliaFil: Piersanti, Mirko. National Institute For Nuclear Physics, University Of T; ItaliaFil: Cesaroni, Claudio. Istituto Nazionale di Geofisica e Vulcanologia; ItaliaFil: Materassi, Massimo. National Research Council, Institute For Complex System; ItaliaFil: Cicone, Antonio. Department Of Information Engineering, Computer Science; ItaliaFil: Alfonsi, Lucilla. Istituto Nazionale di Geofisica e Vulcanologia; ItaliaFil: Romano, Vicenzo. Istituto Nazionale di Geofisica e Vulcanologia; ItaliaFil: Ezquer, Rodolfo Gerardo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y TecnologĂa. Departamento de FĂsica. Laboratorio de IonĂłsfera; Argentina. Universidad TecnolĂłgica Nacional; Argentin
Effects of transient water mass redistribution associated with a tsunami wave on Earth's pole path
We have quantified the effects of a water mass redistribution associated with the propagation of a tsunami wave
on the Earths pole path and on the Length-Of-Day (LOD) and applied our modeling results to the tsunami following
the 2004 giant Sumatra earthquake. We compared the result of our simulations on the instantaneous rotational
axis variations with the preliminary instrumental evidence on the pole path perturbation (which has not
been confirmed) registered just after the occurrence of the earthquake. The detected perturbation in the pole path
showed a step-like discontinuity that cannot be attributed to the effect of a seismic dislocation. Our results show
that the tsunami induced instantaneous rotational pole perturbation is indeed characterized by a step-like discontinuity
compatible with the observations but its magnitude is almost one hundred times smaller than the detected
one. The LOD variation induced by the water mass redistribution turns out to be not significant because the
total effect is smaller than current measurements uncertainties
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