Gas infall and stochastic star formation in galaxies in the local universe     

Guinevere Kauffmann  Timothy M. Heckman  Gabriella De Lucia  Jarle Brinchmann  Stéphane Charlot  Christy Tremonti  Simon D. M. White  Jon Brinkmann 《Monthly notices of the Royal Astronomical Society》2006,367(4):1394-1408

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Hydrogeological Changes Related to the Umbria–Marche Earthquake of 26 September 1997 (Central Italy)     

Monica?Carro  Mattia?De?AmicisEmail author  Lucia?Luzi 《Natural Hazards》2005,34(3):315-339

Evidences of variations of the hydrologic regime have been observed after the Umbria–Marche seismic sequence, started on September 26th 1997, at the boundary between Umbria and Marche regions, central Italy. In order to quantify the hydrological variations, several data regarding groundwater level, spring discharge and river flow rates, have been collected from local authorities and mineral water companies. They allowed to confine the area affected by anomalies and to quantify the hydrological variations by a comparison with the average yearly regime, estimated from the data referring to previous years. An attempt to identify precursor phenomena has also been carried out. The results of the analysis sustain the close connection of two water reservoirs, the Umbria–Marche ridge and the Valnerina unit, that have both been affected by changes of the hydrologic regime. Two of the river gauge stations registered anomalies several months before the crisis started, acting as earthquake precursors.  相似文献   

Paleoecological and climatic changes of the Upper Lerma Basin, Central Mexico during the Holocene     

Beatriz Ludlow-Wiechers  Lucia Almeida-Leero  Gerald Islebe 《Quaternary Research》2005,64(3):318-332

The record of Almoloya Lake in the Upper Lerma basin starts with the deposition of the late Pleistocene Upper Toluca Pumice layer. The data from this interval indicate a period of climatic instability that lasted until 8500 cal yr B.P., when temperature conditions stabilized, although moisture fluctuations continued until 8000 cal yr B.P. Between 8500 and 5000 cal yr B.P. a temperate climate is indicated by dominance of Pinus. From 5000 to 3000 cal yr B.P. Quercus forest expanded, suggesting a warm temperate climate: a first indication of drier environmental conditions is an increase in grassland between 4200 and 3500 cal yr B.P. During the Late Holocene (3300 to 500 cal yr B.P.) the increase of Pinus and grassland indicates temperate dry conditions, with a considerable increase of Pinus between 1100 and 950 cal yr B.P. At the end of this period, humidity increased. The main tendency during the Holocene was a change from humid to dry conditions. During the Early Holocene, Almoloya Lake was larger and deeper; the changing humidity regime resulted in a fragmented marshland, with the presence of aquatic and subaquatic vegetation types.  相似文献   

Strontium and neodymium isotopic evidence for the heterogeneous nature and development of the mantle beneath Afar (Ethiopia)     

P.J. Betton  L. Civetta 《Earth and Planetary Science Letters》1984,71(1):59-70

Neodymium isotope and REE analyses of recent volcanic rocks and spinel lherzolite nodules from the Afar area are reported. The¹⁴³Nd/¹⁴⁴Nd ratios of the volcanic rocks range from 0.51286 to 0.51304, similar to the range recorded from Iceland. However, the⁸⁷Sr/⁸⁶Sr ratios display a distinctly greater range (0.70328–0.70410) than those reported from the primitive rocks of Iceland. Whole rock samples and mineral separates from the spinel lherzolite nodules exhibit uniform¹⁴³Nd/¹⁴⁴Nd ratios (ca. 0.5129) but varied⁸⁷Sr/⁸⁶Sr ratios in the range 0.70427–0.70528.The SrNd isotope variations suggest that the volcanic rocks may have been produced by mixing between two reservoirs with distinct isotopic compositions. Two possible magma reservoirs in this area are the source which produced the “MORB-type” volcanics in the Red Sea and Gulf of Aden and the anomalous source represented by the nodule suite. The isotopic composition of the volcanics is compatible with mixing between these two reservoirs.It is shown that the anomalous source with a high⁸⁷Sr/⁸⁶Sr ratio cannot have been produced by simple processes of partial melting and mixing within normal mantle. Instead the high⁸⁷Sr/⁸⁶Sr is equated with a fluid phase. A primitive cognate fluid, subducted seawater or altered oceanic lithosphere may have been responsible for the generation of the source with a high⁸⁷Sr/⁸⁶Sr ratio.  相似文献   

A robust empirical model to estimate earthquake-induced excess pore water pressure in saturated and non-saturated soils     

Mele  Lucia  Chiaradonna  Anna  Lirer  Stefania  Flora  Alessandro 《Bulletin of Earthquake Engineering》2021,19(10):3865-3893

In engineering practice, the liquefaction potential of a sandy soil is usually evaluated with a semi-empirical, stress-based approach computing a factor of safety in free field conditions, defined as the ratio between the liquefaction resistance (capacity) and the seismic demand. By so doing, an estimate of liquefaction potential is obtained, but nothing is known on the pore pressure increments (often expressed in the form of normalized pore pressure ratio r_u) generated by the seismic action when the safety factor is higher than 1. Even though r_u can be estimated using complex numerical analyses, it would be extremely useful to have a simplified procedure to estimate them consistent with the stress-based approach adopted to check the safety conditions. This paper proposes such a procedure with reference to both saturated and unsaturated soils, considering the latter as soils for which partial saturation has been artificially generated with some ground improvement technology to increase cyclic strength and thus tackle liquefaction risk. A simple relationship between the liquefaction free field safety factor FS, and r_u(S_r) is introduced, that generalizes a previous expression proposed by Chiaradonna and Flora (Geotech Lett, 2020. https://doi.org/10.1680/jgele.19.00032) for saturated soils. The new procedure has been successfully verified against some experimental data, coming from laboratory constant amplitude cyclic tests and from centrifuge tests with irregular acceleration time histories for soils having different gradings and densities.

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Flood disaster subcultures in The Netherlands: the parishes of Borgharen and Itteren     

Karen Engel  Georg Frerks  Lucia Velotti  Jeroen Warner  Bart Weijs 《Natural Hazards》2014,73(2):859-882

The Netherlands knows a persistent threat of flooding. To adapt to this dangerous reality, the Dutch have cultivated what disaster research literature has labeled ‘disaster subcultures’ or a set of cultural (tangible and intangible) tools to deal with the recurrent hazard. While there is abundant attention for the way the Dutch ‘coastal’ and ‘low-lying’ communities deal with the recurrent threat of (coastal) flooding, less is known about the way the Dutch ‘high-lands’ deal with the yearly threat of (fluvial) flooding. This article presents the findings of an explorative research endeavor (2011–2013) aimed at discerning if the disaster subculture concept has contemporary relevance in the Netherlands, particularly with respect to flooding, and if so, whether applying this lens would reveal more about the nature of existing disaster subcultures. Because less is known about the Dutch ‘high-lands,’ we chose to look into the existence and attributes of disaster subcultures in the parishes Borgharen and Itteren, which experience a systematic threat of flooding. Our findings suggest that the disaster subculture lens is valuable as it enables the empirical appreciation of disaster subcultures, even in a small country like the Netherlands, and it unveiled elements of these neighboring parishes’ flood reality that otherwise might have gone unnoticed and that seem central to understanding these two parishes’ levels of vulnerability and resilience. It is our contention that the concept ‘disaster subculture’ makes a greater understanding possible of the cultural context from which vulnerability and resilience to specific and recurrent threats emerge.  相似文献   

Seismic characterization of hyperconcentrated flows in a volcanic environment          下载免费PDF全文

Velio Coviello  Lucia Capra  Rosario Vázquez  Victor H. Márquez-Ramírez 《地球表面变化过程与地形》2018,43(10):2219-2231

We present direct observations and monitoring data of a hyperconcentrated flow that occurred along La Lumbre ravine, one of the most active channels of Volcán de Colima in Mexico. Flow properties were inferred from video images and seismic data recorded by a geophone installed outside the channel. We collected flow samples 400 m upstream from the monitoring station and analyzed the variation of sediment concentration and grain‐size distribution over time. A joint analysis of hydrological (i.e. flow velocity, wetted perimeter) and rheological (i.e. yield stress τ_y and dynamic viscosity μ_m ) parameters was performed to characterize the flow. Different flow regimes and sediment transport processes were identified and analyzed in comparison with both the amplitude and spectral features of the seismic signal. We observed differing sediment concentrations at the same discharge, suggesting a decoupling between sediment transport processes and discharge for low‐magnitude flows. A straightforward correlation was found between the amplitude of the seismic signal and the sediment concentration, and a value of 1.8 × 10^?3 mm/s was identified that can be used as a threshold to recognize the hyperconcentrated phase of the flow. This information was tested on the complete seismic dataset gathered at La Lumbre ravine during the 2015 rainy season. We identified the transition from streamflow to hyperconcentrated flow (and/or vice versa) in 16 low‐magnitude events and we validated this result using the video recordings. The correlation between seismic amplitude and sediment concentration is valid at La Lumbre ravine but would need to be tested in other locations for the development of automatic flow classification methods. This work contributes to standardized seismic methods for characterizing flow processes in volcanic environments, also for the development of lahar early warning systems. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献