Lava flow hazard at Nyiragongo Volcano,DRC     

Giuseppe D. Chirico  Massimiliano Favalli  Paolo Papale  Enzo Boschi  Maria Teresa Pareschi  Arthur Mamou-Mani 《Bulletin of Volcanology》2009,71(4):375-387

Mt. Nyiragongo is one of the most dangerous volcanoes in the world for the risk associated with the propagation of lava flows. In 2002 several vents opened along a huge system of fractures, pouring out lava which reached and destroyed a considerable part of Goma, a town of about 500,000 inhabitants on the shore of Lake Kivu. In a companion paper (Favalli et al. in Bull Volcanol, this issue, 2008) we employed numerical simulations of probable lava flow paths to evaluate the lava flow hazard on the flanks of the volcano, including the neighbouring towns of Goma (DRC) and Gisenyi (Rwanda). In this paper we use numerical simulations to investigate the possibility of significantly reducing the lava flow hazard in the city through the construction of protective barriers. These barriers are added to the DEM of the area as additional morphological elements, and their effect is evaluated by repeating numerical simulations with and without the presence of barriers. A parametric study on barrier location, size, shape and orientation led to the identification of barriers which maximize protection while minimizing their impact. This study shows that the highest hazard area corresponding to eastern Goma, which was largely destroyed by lava flows in 2002, cannot be effectively protected from future lava flows towards Lake Kivu and should be abandoned. On the contrary, the rest of the town can be sheltered from lava flows by means of two barriers that deviate or contain the lava within the East Goma sector. A proposal for the future development of the town is formulated, whereby “new” Goma is completely safe from the arrival of lava flows originating from vents outside its boundaries. The proposal minimizes the risk of further destruction in town due to future lava flows.  相似文献   

Lava flow hazard at Nyiragongo volcano,D.R.C.     

Massimiliano Favalli  Giuseppe D. Chirico  Paolo Papale  Maria Teresa Pareschi  Enzo Boschi 《Bulletin of Volcanology》2009,71(4):363-374

The 2002 eruption of Nyiragongo volcano constitutes the most outstanding case ever of lava flow in a big town. It also represents one of the very rare cases of direct casualties from lava flows, which had high velocities of up to tens of kilometer per hour. As in the 1977 eruption, which is the only other eccentric eruption of the volcano in more than 100 years, lava flows were emitted from several vents along a N–S system of fractures extending for more than 10 km, from which they propagated mostly towards Lake Kivu and Goma, a town of about 500,000 inhabitants. We assessed the lava flow hazard on the entire volcano and in the towns of Goma (D.R.C.) and Gisenyi (Rwanda) through numerical simulations of probable lava flow paths. Lava flow paths are computed based on the steepest descent principle, modified by stochastically perturbing the topography to take into account the capability of lava flows to override topographic obstacles, fill topographic depressions, and spread over the topography. Code calibration and the definition of the expected lava flow length and vent opening probability distributions were done based on the 1977 and 2002 eruptions. The final lava flow hazard map shows that the eastern sector of Goma devastated in 2002 represents the area of highest hazard on the flanks of the volcano. The second highest hazard sector in Goma is the area of propagation of the western lava flow in 2002. The town of Gisenyi is subject to moderate to high hazard due to its proximity to the alignment of fractures active in 1977 and 2002. In a companion paper (Chirico et al., Bull Volcanol, in this issue, 2008) we use numerical simulations to investigate the possibility of reducing lava flow hazard through the construction of protective barriers, and formulate a proposal for the future development of the town of Goma.  相似文献   

2009年意大利中部阿奎拉地震DInSAR同震位移的有限断层反演     

S·Atzori  I·Hunstad  M·Chini  S·Salvi  C·Tolomei  C·Bignami  S·Stramondo  E·Trasatti  A·Antonioli  E·Boschi  李晶 《世界地震译丛》2009,(4):30-36

根据环境卫星Envisat和COSMO—SkyMed模型（为同震位错研究而首次设计的X波段反演干涉图）的DInSAR干涉图,确定了2009年4月6日阿奎拉Mw=6．3级地震时激发的断层几何形状及运动特征。我们的主震最佳拟合解为一个约16km长、12km宽的正断层,存在小的右旋分量,向西南倾斜47°,最大滑动约90cm。虽然地震位错可能只有1km深,但是断层面的上倾投影与标绘的帕加尼卡-南德米特里奥断层的北段相符合,在现场观察到了该断层地表破裂的迹线。该断层在现有震源目录中的缺失表明,需要对具体的地表和地下进行进一步的地质和地球物理勘测,以便对局部规模的地震危险性做出更准确的评估。  相似文献   

Conjugate Points in the Gravitational n-Body Problem     

Angelo B. Mingarelli  Chiara M. F. Mingarelli 《Celestial Mechanics and Dynamical Astronomy》2005,91(3-4):391-401

In an effort to understand the nature of almost periodic orbits in the n-body problem (for all time t) we look first to the more basic question of the oscillatory nature of solutions of this problem (on a half-line, usually taken as R ⁺). Intimately related to this is the notion of a conjugate point(due to A. Wintner) of a solution. Specifically, by rewriting the mass unrestricted general problem of n-bodies in a symmetric form we prove that in the gravitational Newtonian n-body problem with collisionless motions there exists arbitrarily large conjugate points in the case of arbitrary (positive) masses whenever the cube of the reciprocal of at least one of the mutual distances is not integrable at infinity. The implication of this result is that there are possibly many Wintner oscillatorysolutions in these cases (some of which may or may not be almost periodic). As a consequence, we obtain sufficient conditions for all continuable solutions (to infinity) to be either unbounded or to allow for near misses (at infinity). The results also apply to potentials other than Newtonian ones. Our techniques are drawn from results in systems oscillation theory and are applicable to more general situations. Dedicated to the memory of Robert M. (Bob) Kauffman, formerly Professor of the University of Alabama in Birmingham  相似文献   

Isotopic and element exchange during serpentinization and metasomatism at the Atlantis Massif (MAR 30°N): Insights from B and Sr isotope data     

Chiara Boschi  Andrea Dini  Deborah S. Kelley 《Geochimica et cosmochimica acta》2008,72(7):1801-1823

The Lost City hydrothermal system at the southern Atlantis Massif (Mid-Atlantic Ridge, 30°N) provides a natural laboratory for studying serpentinization processes, the temporal evolution of ultramafic-hosted hydrothermal systems, and alteration conditions during formation and emplacement of an oceanic core complex. Here we present B, O, and Sr isotope data to investigate fluid/rock interaction and mass transfer during detachment faulting and exhumation of lithospheric sequences within the Atlantis Massif. Our data indicate that extensive serpentinization was a seawater-dominated process that occurred predominately at temperatures of 150-250 °C and at high integrated W/R ratios that led to a marked boron enrichment (34-91 ppm). Boron removal from seawater during serpentinization is positively correlated with changes in δ¹¹B (11-16‰) but shows no correlation with O-isotope composition. Modeling indicates that B concentrations and isotope values of the serpentinites are controlled by transient temperature-pH conditions. In contrast to prior studies, we conclude that low-temperature marine weathering processes are insignificant for boron geochemistry of the Atlantis Massif serpentinites. Talc- and amphibole-rich fault rocks formed within a zone of detachment faulting at temperatures of approximately 270-350 °C and at low W/R ratios. Talc formation in ultramafic domains in the massif was subsequent to an early stage of serpentinization and was controlled by the access of Si-rich fluids derived through seawater-gabbro interactions. Replacement of serpentine by talc resulted in boron loss and significant lowering of δ¹¹B values (9-10‰), which we model as the product of progressive extraction of boron. Our study provides new constraints on the boron geochemical cycle at oceanic spreading ridges and suggests that serpentinization associated with ultramafic-hosted hydrothermal systems may have important implications for the behavior of boron in subduction zone settings.  相似文献   

Strain rates in the Alpine Mediterranean region: insights from advanced techniques of data processing     

Gregorio Farolfi  Chiara Del Ventisette 《GPS Solutions》2017,21(3):1027-1036

Strain rates and Euler poles for various subregions of the Alpine Mediterranean region were calculated by using global navigation satellite system data from permanent stations. The main scope of the study is to compare and analyze strain rate maps that were calculated using different approaches. This area presents a complex tectonic setting due to the interaction of the Eurasian and Nubian plates. The horizontal velocity gradient tensor was computed starting from a new set of site velocities determined by using continuous long-series geodetic data, state-of-the-art antenna calibrations and recomputed precise orbits. Geodesy provides velocities for a sparsely distributed, discrete number of sites, while deformation has a spatially continuous distribution. For this reason, the interpolation method and the geometric approach to the problem play a fundamental role in the estimation of the strain rate field. In the present study, principal deformation axes and principal angle were estimated by applying two different approaches: the Delaunay triangulation and a grid solution. Both methods produce results with broad coherence, providing new information about the deformation throughout the entire study area. Moreover, an evaluation and analysis of Euler poles related to the different velocity patterns, give complementary information to reconstruct the active deformation in the Mediterranean area.  相似文献   

Investigating fossil hydrothermal systems by means of fluid inclusions and stable isotopes in banded travertine: an example from Castelnuovo dell’Abate (southern Tuscany,Italy)     

Valentina Rimondi  Pilario Costagliola  Giovanni Ruggieri  Marco Benvenuti  Chiara Boschi  Andrea Brogi  Enrico Capezzuoli  Guia Morelli  Massimo Gasparon  Domenico Liotta 《International Journal of Earth Sciences》2016,105(2):659-679

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Time-dependent ground movements induced by shield tunneling in soft clay: a parametric study     

Elisabetta Cattoni  Chiara Miriano  Laura Boco  Claudio Tamagnini 《Acta Geotechnica》2016,11(6):1385-1399

In this work, the effects of coupled hydromechanical (consolidation) processes associated with shield tunneling excavation in soft clays are investigated with particular attention to the prediction of ground movements at the ground surface. A series of 2d FE analyses have been carried out in parametric form in order to investigate the effects of tunnel excavation velocity relative to the soil consolidation rate and the hydraulic boundary conditions at the tunnel boundary. The shield advancement process has been simulated with a simplified procedure incorporating both volume loss and ovalization of the tunnel section. In order to investigate the relative importance of soil consolidation during the excavation process, different characteristic times for the tunnel face advancement and for the consolidation process around the tunnel have been considered, for the two limiting conditions of fully permeable liner and impervious liner. The potential damage induced by the tunnel excavation on existing structures, based on computed ground surface distortions and horizontal deformations, has been found to vary significantly with time during the consolidation process. The results of the simulations allowed to obtain useful information on the minimum tunnel face advancement speed for which the assumption of fully undrained conditions for the soil during the excavations is acceptable, as well as on the speed range for which solving the fully coupled hydromechanical problem is necessary.  相似文献   

The Stancari air thermometer and the 1715–1737 record in Bologna,Italy     

Dario Camuffo  Antonio della Valle  Chiara Bertolin  Elena Santorelli 《Climatic change》2016,139(3-4):623-636

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The micrometeorite flux to Earth during the earliest Paleogene reconstructed in the Bottaccione section (Umbrian Apennines), Italy     

Samuele Boschi  Birger Schmitz  Ellinor Martin  Fredrik Terfelt 《Meteoritics & planetary science》2020,55(7):1615-1628

Based on sediment‐dispersed extraterrestrial spinel grains in the Bottaccione limestone section in Italy, we reconstructed the micrometeorite flux to Earth during the early Paleocene. From a total of 843 kg of limestone, 86 extraterrestrial spinel grains (12 grains > 63 μm, and 74 in the 32–63 μm fraction) have been recovered. Our results indicate that the micrometeorite flux was not elevated during the early Paleocene. Ordinary chondrites dominated over achondritic meteorites similar to the recent flux, but H chondrites dominated over L and LL chondrites (69%, 22%, and 9%, respectively). This H‐chondrite dominance is similar to that recorded within an enigmatic ³He anomaly (70, 27, and 3%) in the Turonian, but different from just before this ³He anomaly and in the early Cretaceous, where ratios are similar to the recent flux (~45%, 45%, and 10%). The K‐Ar isotopic ages of recently fallen H chondrites indicate a small impact event on the H‐chondrite parent body ~50 to 100 Ma ago. We tentatively suggest that this event is recorded by the Turonian ³He anomaly, resulting in an H‐chondrite dominance up to the Paleocene. Our sample spanning the 20 cm above the Cretaceous–Paleogene (K–Pg) boundary did not yield any spinel grains related to the K–Pg boundary impactor.  相似文献