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11.
Salvatore Alparone Graziella Barberi Alessandro Bonforte Vincenza Maiolino Andrea Ursino 《Bulletin of Volcanology》2011,73(7):869-885
We carried out a study of the seismicity and ground deformation occurring on Mt. Etna volcano after the end of the 2002–2003
eruption and before the onset of the 2004–2005 eruption. Data were recorded by the permanent local seismic network run by
Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Catania and by geodetic surveys carried out in July 2003 and July 2004 on the GPS network. Most earthquakes were grouped in two main
clusters located in the northeastern and southeastern sectors of the volcano. The areal distribution of seismic energy associated
with the recorded earthquakes allowed us to highlight the main seismogenic areas of Mt. Etna. In order to better understand
the kinematic processes of the volcano, 3D seismic locations were used to compute fault plane solutions, and a selected dataset
was inverted to determine stress and strain tensors. The focal mechanisms in the northeastern sector show clear left-lateral
kinematics along an E-W fault plane, consistent with events occurring along the Pernicana Fault system. The fault plane solutions
in the southeastern sector show mainly right-lateral kinematics along a NNE and ENE fault plane and left lateral-kinematics
along NW fault planes that together suggest roughly E-W oriented compression. Surface ground deformation affecting Mt. Etna
measured by GPS surveys highlighted a marked inflation during the same period and exceptionally strong seawards motion of
its eastern flank. The 2D geodetic strain tensor distribution was calculated and the results show mainly ENE-WSW extension
coupled with WNW-ESE contraction, indicating right-lateral shear along a NW-SE oriented fault plane. The different deformation
of the eastern sector of the volcano, as measured by seismicity and ground deformation, must be interpreted by considering
the different depths of the two signals. Seismic activity in the southeastern sector of volcano is located between 3 and 8 km b.s.l.
and can be associated with a very strong additional E-W compression induced by a pressurizing source just westwards and at
the same depth, located by inverting GPS data. Ground deformation, in contrast, is mainly affected by the shallower dynamics
of the fast moving eastern flank which produces a shallower opposing E-W extension. The entire dataset shows that two different
processes affect the eastern flank at the same time but at different depths; the boundary is clearly located at a depth of
3 km b.s.l. and could represent the décollement surface for the mobile flank. 相似文献
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Land—ocean transfer of sediment and organic matter along the Moroccan Atlantic margin (NW Africa) seems to have been very effective during the last 130 ka. In a marine core from this region, we found total organic carbon (TOC) values ranging from 0.3 to 1.7 dry wt% of bulk sediments. These relatively high values are fairly unusual, as the core was recovered from an open-ocean environment that is currently oligotrophic. In order to explain this trend, more typical of an upwelling eutrophic setting, three processes were evaluated: (1) in situ primary production associated with the extension of the Cape Ghir upwelling filament, (2) bottom water conditions that may favour organic carbon preservation and (3) lateral organic carbon advection. The site occasionally experienced more eutrophic conditions, especially during termination I; here, we recorded a relative high abundance of the planktonic foraminifer Globigerina bulloides, suggesting high primary production. However, given the absence of correlation between TOC and G. bulloides records, high TOC storage cannot be attributed exclusively to primary production. Preservation factors such as bottom water ventilation are also ruled out. Lateral TOC advection seems to be the most plausible process. Today, lateral advection and offshore transport of nutrients and organic matter characterize the study region. However, the triggering mechanisms deserve further investigation. Different controlling factors influencing the mobilization and advection of organic carbon from coastal upwelling sites to the deep basin are discussed. The correlation found between down-core TOC and sea-level changes suggests sea-level fluctuations as the most effective mechanism driving nepheloid layer detachment and seaward material transport. 相似文献
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In the western hemisphere of Mars Amazonian volcanism from Arsia Mons produced the smooth surfaces of Daedalia Planum and masks older rocks. Close to the southern termination of Daedalia Planum basement rocks are exposed in which are preserved craters that escaped or were only partially filled by this most recent volcanism. Pickering Crater is an approximately 130 km diameter crater. The youngest lavas flowed into this crater from Daedalia Planum by way of a NW rim breach, covering its western part. East of a well-defined flow front an older lava sequence with a distinctive platy surface and derived from a more proximal unestablished source to the northeast is exposed. Several units are identified within this sequence on the basis of surface texture, which is more subdued in progressively older rocks. Only local mapping of the flow front boundaries of these units is possible because of incomplete coverage by high resolution imagery. During emplacement of the older lavas a NE-SW striking en echelon graben system and parallel smaller troughs and dikes formed under inferred regional NW-SE extension. A much earlier strike-slip regime pre-dating the lavas exposed in the crater floor is postulated, based on the highly fretted nature of the rim of Pickering Crater and an elongated smaller crater to its northeast, approximately 40 km long in the NE-SW direction. The rims of these craters contrast with that of a smoother rimmed impact crater in the southeast that was excavated subsequent to strike-slip deformation but prior to the emplacement of platy surfaced lavas. 相似文献
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Kevin M. Scott James W. Vallance Norman Kerle Jose Luis Macías Wilfried Strauch Graziella Devoli 《地球表面变化过程与地形》2005,30(1):59-79
A catastrophic lahar began on 30 October 1998, as hurricane precipitation triggered a small ?ank collapse of Casita volcano, a complex and probably dormant stratovolcano. The initial rockslide‐debris avalanche evolved on the ?ank to yield a watery debris ?ood with a sediment concentration less than 60 per cent by volume at the base of the volcano. Within 2·5 km, however, the watery ?ow entrained (bulked) enough sediment to transform entirely to a debris ?ow. The debris ?ow, 6 km downstream and 1·2 km wide and 3 to 6 m deep, killed 2500 people, nearly the entire populations of the communities of El Porvenir and Rolando Rodriguez. These ‘new towns’ were developed in a prehistoric lahar pathway: at least three ?ows of similar size since 8330 14C years bp are documented by stratigraphy in the same 30‐degree sector. Travel time between perception of the ?ow and destruction of the towns was only 2·5–3·0 minutes. The evolution of the ?ow wave occurred with hydraulic continuity and without pause or any extraordinary addition of water. The precipitation trigger of the Casita lahar emphasizes the need, in volcano hazard assessments, for including the potential for non‐eruption‐related collapse lahars with the more predictable potential of their syneruption analogues. The ?ow behaviour emphasizes that volcano collapses can yield not only volcanic debris avalanches with restricted runouts, but also mobile lahars that enlarge by bulking as they ?ow. Volumes and hence inundation areas of collapse‐runout lahars can increase greatly beyond their sources: the volume of the Casita lahar bulked to at least 2·6 times the contributing volume of the ?ank collapse and 4·2 times that of the debris ?ood. At least 78 per cent of the debris ?ow matrix (sediment < ?1·0Φ; 2 mm) was entrained during ?ow. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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We propose a strategy for detecting and analyzing optical afterglows (OAs) of long gamma-ray bursts (GRBs) without the need to obtain their light curves. This approach is useful for the Gaia satellite, which provides sampled optical ultra-low-dispersion spectroscopic observations of the sky. For this purpose, we show that most OAs of long GRBs display specific values of some of their color indices, representing synchrotron emission of the jet. They are stable in time during the event. These indices, which can be determined from the spectra, are very similar for the ensemble of OAs with redshift z < 3.5 and display a strong clustering in some color-color diagrams. These indices also enable to constrain the properties of the local interstellar medium of GRBs. The long-lasting mapping of the sky with the Gaia instruments also gives us a hope to search for the so-called orphan afterglows, which, according to some authors, can be considerably more numerous than OAs of the observed GRBs. We also show how to resolve OAs from other transients in the Gaia data. The color indices and the properties of the quiescent sources (host galaxies of OAs detectable later by the large ground-based telescopes at the co-ordinates of the OA determined by Gaia) would tell us which one, among transients detected by Gaia, is a GRB OA. 相似文献
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Salvatore Alparone Graziella Barberi Elisabetta Giampiccolo Vincenza Maiolino Antonino Mostaccio Carla Musumeci Antonio Scaltrito Luciano Scarfì Tiziana Tuv Andrea Ursino 《地学学报》2020,32(5):334-344
3D earthquake locations, focal mechanisms and stress tensor distribution in a 16‐month interval covering the 2018 Mt. Etna flank eruption, enabled us to investigate the relationship between magma intrusion and structural response of the volcano and shed light on the dynamic processes affecting the instability of Mt. Etna. The magma intrusion likely caused tension in the flanks of the volcano, leading to significant ground deformation and redistribution of stress on the neighbouring faults at the edge of Mt. Etna's unstable sector, encouraging the ESE sliding of the eastern flank of the volcano. Accordingly, FPSs of the post‐eruptive events show strike slip faulting mechanisms, under a stress regime characterized by a maximum compressive σ1, NE‐SW oriented. In this perspective, any flank eruption could temporarily enhance the sliding process of both the southern and eastern flanks of the volcano. 相似文献
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AXIOM: advanced X-ray imaging of the magnetosphere 总被引：1，自引：0，他引：1
Graziella Branduardi-Raymont Steve F. Sembay Jonathan P. Eastwood David G. Sibeck Tony A. Abbey Patrick Brown Jenny A. Carter Chris M. Carr Colin Forsyth Dhiren Kataria Steve Kemble Steve E. Milan Chris J. Owen Lisa Peacocke Andy M. Read Andrew J. Coates Michael R. Collier Stan W. H. Cowley Andrew N. Fazakerley George W. Fraser Geraint H. Jones Rosine Lallement Mark Lester F. Scott Porter Tim K. Yeoman 《Experimental Astronomy》2012,33(2-3):403-443
Planetary plasma and magnetic field environments can be studied in two complementary ways—by in situ measurements, or by remote sensing. While the former provide precise information about plasma behaviour, instabilities and dynamics on local scales, the latter offers the global view necessary to understand the overall interaction of the magnetospheric plasma with the solar wind. Some parts of the Earth’s magnetosphere have been remotely sensed, but the majority remains unexplored by this type of measurements. Here we propose a novel and more elegant approach employing remote X-ray imaging techniques, which are now possible thanks to the relatively recent discovery of solar wind charge exchange X-ray emissions in the vicinity of the Earth’s magnetosphere. In this article we describe how an appropriately designed and located X-ray telescope, supported by simultaneous in situ measurements of the solar wind, can be used to image the dayside magnetosphere, magnetosheath and bow shock, with a temporal and spatial resolution sufficient to address several key outstanding questions concerning how the solar wind interacts with the Earth’s magnetosphere on a global level. Global images of the dayside magnetospheric boundaries require vantage points well outside the magnetosphere. Our studies have led us to propose ‘AXIOM: Advanced X-ray Imaging of the Magnetosphere’, a concept mission using a Vega launcher with a LISA Pathfinder-type Propulsion Module to place the spacecraft in a Lissajous orbit around the Earth–Moon L1 point. The model payload consists of an X-ray Wide Field Imager, capable of both imaging and spectroscopy, and an in situ plasma and magnetic field measurement package. This package comprises a Proton-Alpha Sensor, designed to measure the bulk properties of the solar wind, an Ion Composition Analyser, to characterise the minor ion populations in the solar wind that cause charge exchange emission, and a Magnetometer, designed to measure the strength and direction of the solar wind magnetic field. We also show simulations that demonstrate how the proposed X-ray telescope design is capable of imaging the predicted emission from the dayside magnetosphere with the sensitivity and cadence required to achieve the science goals of the mission. 相似文献