185 research outputs found
Relativity accommodates superluminal mean velocities
Contrary to a widespread belief, measures of velocity can yield a value
larger than , the instantaneous light speed in vacuum, without contradicting
Einstein's relativity. Nevertheless, the effect turns out to be too small to
explain the recently claimed superluminal velocity by the OPERA collaboration.
Several other general relativistic effects acting on the OPERA neutrinos are
also analyzed. All of them are unable to explain the OPERA result.Comment: 5 pages; Latex source, 2 eps figures (expanded discussion, a few
typos corrected, some refs. added
Fault on-off versus coseismic fluids reaction
AbstractThe fault activation (fault on) interrupts the enduring fault locking (fault off) and marks the end of a seismic cycle in which the brittle-ductile transition (BDT) acts as a sort of switch. We suggest that the fluid flow rates differ during the different periods of the seismic cycle (interseismic, pre-seismic, coseismic and post-seismic) and in particular as a function of the tectonic style. Regional examples indicate that tectonic-related fluids anomalies depend on the stage of the tectonic cycle and the tectonic style. Although it is difficult to model an increasing permeability with depth and several BDT transitions plus independent acquicludes may occur in the crust, we devised the simplest numerical model of a fault constantly shearing in the ductile deeper crust while being locked in the brittle shallow layer, with variable homogeneous permeabilities. The results indicate different behaviors in the three main tectonic settings. In tensional tectonics, a stretched band antithetic to the normal fault forms above the BDT during the interseismic period. Fractures close and fluids are expelled during the coseismic stage. The mechanism reverses in compressional tectonics. During the interseismic stage, an over-compressed band forms above the BDT. The band dilates while rebounding in the coseismic stage and attracts fluids locally. At the tip lines along strike-slip faults, two couples of subvertical bands show different behavior, one in dilation/compression and one in compression/dilation. This deformation pattern inverts during the coseismic stage. Sometimes a pre-seismic stage in which fluids start moving may be observed and could potentially become a precursor
The westward drift of the lithosphere. A tidal ratchet?
Is the westerly rotation of the lithosphere an ephemeral accidental recent phenomenon or is it a stable
process of Earthâs geodynamics? The reason why the tidal drag has been questioned as the mechanism
determining the lithospheric shift relative to the underlying mantle is the apparent too high viscosity of
the asthenosphere. However, plate boundaries asymmetries are a robust indication of the âwesterlyâ
decoupling of the entire Earthâs outer lithospheric shell and new studies support lower viscosities in the
low-velocity layer (LVZ) atop the asthenosphere. Since the solid Earth tide oscillation is longer in one side
relative to the other due to the contemporaneous Moonâs revolution, we demonstrate that a non-linear
rheological behavior is expected in the lithosphere mantle interplay. This may provide a sort of ratchet
favoring lowering of the LVZ viscosity under shear, allowing decoupling in the LVZ and triggering the
westerly motion of the lithosphere relative to the mantle
The first ultra-high resolution Digital Terrain Model of the shallow-water sector around Lipari Island (Aeolian Islands, Italy)
Very high resolution bathymetric map obtained through multibeam echosounders
data are crucial to generate accurate Digital Terrain Models
from which the morphological setting of active volcanic areas can be analyzed
in detail. Here we show and discuss the main results from the first
multibeam bathymetric survey performed in shallow-waters around the island
of Lipari, the largest and the most densely populated of the Aeolian
Islands (southern Italy). Data have been collected in the depth range of
0.1-150 m and complete the already existent high-resolution multibeam
bathymetry realized between 100 and 1300 m water depth. The new ultrahigh
resolution bathymetric maps at 0.1-0.5 m provide new insights on the
shallow seafloor of Lipari, allowing to detail a large spectrum of volcanic,
erosive-depositional and anthropic features. Moreover, the presented data
allow outlining the recent morphological evolution of the shallow coastal
sector of this active volcanic island, indicating the presence of potential
geo-hazard factors in shallow waters
Longer aftershocks duration in extensional tectonic settings
Aftershocks number decay through time, depending on several parameters peculiar to each seismogenic regions, including mainshock magnitude, crustal rheology, and stress changes along
the fault. However, the exact role of these parameters in controlling the duration of the aftershock sequence is still unknown. Here, using two methodologies, we show that the tectonic setting primarily controls the duration of aftershocks. On average and for a given mainshock magnitude (1) aftershock sequences are longer and (2) the number of earthquakes is greater in extensional tectonic settings than in contractional ones. We interpret this difference as related to the different type of energy dissipated during earthquakes. In detail, (1) a joint effect of gravitational forces and pure elastic stress release governs extensional earthquakes, whereas (2) pure elastic stress release controls contractional earthquakes. Accordingly, normal faults operate in favour of gravity, preserving inertia for a longer period and seismicity lasts until gravitational equilibrium is reached. Vice versa, thrusts act against gravity, exhaust their inertia faster and the elastic energy dissipation is buffered by the gravitational force. Hence, for seismic sequences of comparable magnitude and rheological parameters, aftershocks last longer in extensional settings because gravity favours the collapse of the hangingwall volumes
Present geodynamics of the northern Adriatic plate
The northern Adriatic plate is surrounded and squeezed by three orogens
(i.e. Apennines, Alps and Dinarides). Therefore, in the same area, the effects of
three independent subduction zones coexist and overlap. This supports the
evidence that plate boundaries are passive features.
The northeastward migration of the Apennines subduction hinge
determines the present-day faster subsidence rate in the western side of the
northern Adriatic (>1 mm/yr). This is recorded also by the dip of the foreland
regional monocline, and the increase SW-ward of the depth of the Tyrrhenian
layer, as well as the increase in thickness of the Pliocene and Pleistocene
sediments. These data indicate the dominant influence of the Apennines
subduction and the related asymmetric subsidence in the northern Adriatic
realm. The Dinarides front has been subsided by the Apennines subduction
hinge, as shown by the eroded Dalmatian anticlines in the eastern Adriatic Sea.
GPS data show the horizontal pattern of motion along the front of the three
belts surrounding the northern Adriatic plate. Values of shortening along the
prisms are in the order of 2-3 mm/yr (Northern Apennines), 1-2 mm/yr
(Southern Alps) and <1mm/yr (Dinarides). The pattern of the new GPS
velocities relative to Eurasia account for different tectonic domains and the
estimated strain rates are within 0.1 ÎŒstrain/yr. The shortening directions tend
to be perpendicular to the thrust belt fronts, as expected. The areas where the
strain rate sharply decreases across a tectonic feature (e.g., the Ferrara salient)
are considered structures seismically loading the brittle laye
Static stress drop as determined from geodetic strain rates and statistical seismicity
Two critical items in the energetic budget of a seismic province are the strain rate, which is measured geodetically on the Earthâs 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 [4.5â7.3]. These results for stress drop are independent of the âaâ and âbâ 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
The RING GPS network: a research geodetic infrastructure to study plate boundary deformation in the Central Mediterranean
We present the INGV (Italian National Institute of Geophysics and Volcanology) geodetic research infrastructure
and related facilities, dedicated to the observation and monitoring of current deformation of the plate boundary
between Africa and Eurasia. The recent increase of continuous GPS (CGPS) stations in the Central Mediterranean
plate boundary zone offers the opportunity to study in detail the present-day kinematics of this actively deforming
region. For answering all the open questions related to this complex area, INGV deployed a permanent, integrated
and real-time monitoring CGPS network (RING) all over Italy. The RING network (http:/ring.gm.ingv.it) is now
constituted by more than 150 stations. All stations have high quality GPS monuments and most of them are
co-located with broadband or very broadband seismometers and strong motion sensors. The RING CGPS sites
acquire at 1Hz and 30s sampling rates (some of them acquire at 10 Hz) and are connected in real-time to the
INGV acquisition centers located in Roma and Grottaminarda. Real-time GPS data are transmitted using different
systems, such as satellite systems, Internet, GPRS/UMTS and wireless networks. The differentiation of data
transmission type and the integration with seismic instruments makes this network one of the most innovative
CGPS networks in Europe. Furthermore, the INGV data acquisition centers acquire, archive and analyze most
of the Italian CGPS stations managed by regional or national data providers (such as local Authorities and
nation-wide industries), integrating more than 350 stations of the CGPS scientific and commercial networks
existing in the Italian region. To manage data acquisition, storage, distribution and access we developed dedicated
facilities including new softwares for data acquisition and a web-based collaborative environment for management
of data and metadata. The GPS analysis is carried out with the three main geodetic-quality softwares used in the
GPS scientific community: Bernese GAMIT an GIPSY-OASIS. The resulting daily solutions are aligned to the
ITRF2005 reference frame. Stable plate reference frames are realized by minimizing the horizontal velocities at
sites on the Eurasia and Nubia plates, respectively. The different software-related solutions consistency RMS is
within 0.3 mm/yr (Avallone et al., 2010). The solutions are then evaluated with regard to the numerous scientific
motivations behind this presentation, ranging from the definition of strain distribution and microplate kinematics
within the plate boundary, to the evaluation of tectonic strain accumulation on active faults. The RING network
is strongly contributing to the definition of GPS velocity field in the Italian region, and now is able to furnish
a newly and up to date view of this actively deforming part of the Nubia-Eurasia plate boundary. INGV is now
aiming to make the RING (and integrated CGPS networks) data and related products publicly available for the
scientific community. We believe that our network represents an important reality in the framework of the EPOS
infrastructure and we strongly support the idea of an European research approach to data sharing among the
scientific community. We will present (a) the current CGPS site distribution, (b) the technological description of
the data acquisition, storage and distribution at INGV centers, (c) the results of CGPS data analysis, and (d) the
planned data access for the scientific community.PublishedVienna, Geophysical Research Abstracts
Vol. 13, EGU2011-8626, 20111.9. Rete GPS nazionale3.2. Tettonica attivaope
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