The Colider and Roosevelt Volcanic rocks (sw amazonian craton): geochemistry and sm-nd isotope characteristics of a silicic large igneous province     

Saar de Almeida  Bruna  Geraldes  Mauro César  Sommer  Carlos Augusto  Corrales  Felipe  de Barros  Antonio João Paes 《中国地球化学学报》2021,40(6):1023-1049

The volcanic rocks of the Colíder and Roosevelt formations are extensively exposed in the south-central portion of the Amazonian Craton where effusive and pyroclastic rocks have been mapped. Both units, topped by chemical sediments and oceanic facies as rhyolite and andesite lavas, rhyodacite, and porphyritic dacite, with frequent intercalations of pyroclastic and epiclastic deposits. Whole-rock geochemistry for 55 samples of rhyolitic to andesitic composition suggests the involvement of fertile mantle-derived components with E-MORB to OIB compositions. The analyzed rocks display calc-alkaline to shoshonitic affinity consistent with generation related to an active continental margin. The whole-rock Sm-Nd isotope data from selected felsic volcanic rocks of the Colíder and Roosevelt formations yield negative initial ε_Nd values between –3 and –9, indicating the predominantly crustal nature of the parental magmas with early Archean to late Paleoproterozoic (ca. 2.5–2.0 Ga) depleted mantle model ages.

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Groundwater metering: revisiting a ubiquitous ‘best practice’     

Molle  François  Closas  Alvar 《Hydrogeology Journal》2021,29(5):1857-1870

Hydrogeology Journal - It is often taken for granted that metering is an unarguable ‘best practice’ when it comes to the quantitative management of groundwater resources. This paper...  相似文献   

The effect of cement material properties on the fracture patterns developing within cement-covered brittle sphere under impact     

Jiang  Sheng  Shen  Luming  Guillard  François  Einav  Itai 《Acta Geotechnica》2021,16(3):763-773

Acta Geotechnica - Dynamic loading experiments of single glass bead cement-covered by epoxy resins of different compositions demonstrate the existence of diverse fracture patterns under similar...  相似文献   

Single-particle crushing strength under different relative humidity conditions     

Manso  João  Marcelino  João  Caldeira  Laura 《Acta Geotechnica》2021,16(3):749-761

This paper presents a fundamental study on the effect of the relative humidity on the rockfill crushing strength. This aspect plays an important role in the mechanical behaviour of rockfill, and it is known that certain characteristics of the granular materials, such as compressibility and shear strength, depend on the confining stress, which is a function of the particles crushing. An increased interest has been observed regarding the effect of the relative humidity in the mechanical behaviour of rockfill. Unfortunately, limited research has been conducted until now regarding the study of individual particle crushing. Therefore, this paper thoroughly investigated particle crushing, by performing single-particle crushing tests on rockfill particles divided into four size ranges, under different relative humidity conditions. The experimental results reveal a considerable influence of the relative humidity in the studied rockfill particles, whose strength of the particles with the greatest dimensions in saturated conditions was reduced by half. Consistent macro-mechanical evidence demonstrates that particle’s size and relative humidity conditions depict the most important factors that influence particle crushing strength.

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Stress changes induced at neighbouring faults by the June 2000 earthquakes,South Iceland Seismic Zone     

Romain Plateaux  Jacques Angelier  Françoise Bergerat  Frederic Cappa  Ragnar Stefánsson 《地学学报》2010,22(2):79-86

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Limpets as prey: Lipophrys pholis choice for size     

Ana C. Silva  Ana C. Amador  Sónia Brazão  Claúdia Faria  Diana Boaventura 《Marine Ecology》2010,31(4):525-532

Patellid limpets are key species on rocky shores, structuring intertidal assemblages through their grazing. Their role as prey for fish is, however, often overlooked in studies of intertidal ecosystem functioning. The shanny Lipophrys pholis is a common predator of limpets on rocky shores in Northern Europe and, in this study, we examined the characteristics of its predation on limpets based on prey size. The limpet size range that adult L. pholis (10–12.5 cm) can eat was examined in the laboratory using Patella depressa in 0.2 cm classes, varying between 0.5 cm and 3.0 cm in maximum shell length. There was a limpet size refuge above 1.8 cm, while all smaller sizes were readily consumed by the shanny. The predator attacking behaviour was also examined and found to vary with prey size. Limpets up to 0.8 cm were crushed by the jaw‐constricting force and eaten whole, whereas larger prey were prised from the substratum and the body subsequently separated from the shell. To examine whether there was a L. pholis preference for P. depressa size, a two‐stage laboratory experiment was done using two size classes defined as small (0.7–0.8 cm maximum shell length) and large (1.5–1.6 cm maximum shell length). In the first stage, the predator was given each limpet size class separately. In the second stage, the fish was given a choice between the two classes. Lipophrys pholis was shown to have a preference for the large size class (1.5–1.6 cm). The average number of limpets consumed by the shanny was examined for the duration of one high‐tide typical of the central region of Portugal (≈ 4 h). On average, approximately five limpets (up to an eight limpet maximum) were consumed. The present study shows that L. pholis has a feeding preference based on limpet size, which suggests that the limpet population structure and intra‐ and inter‐specific interactions may be influenced by the shanny predation.  相似文献   

Evaluation of site conditions for the Ankara Basin of Turkey based on seismic site characterization of near-surface geologic materials     

M.K. Koçkar  H. Akgün  E.M. Rathje 《Soil Dynamics and Earthquake Engineering》2010,30(1-2):8-20

Regional site conditions relevant for seismic hazard studies can be derived from various geologic, seismologic, and geotechnical sources. In this study, site conditions are derived for the Ankara Basin in Turkey by merging in-situ seismic measurements of dynamic properties, geologic information, and some geotechnical boring information. Field seismic refraction surveys were performed at 259 sites in the project area to classify and characterize Plio–Pleistocene fluvial deposits and Quaternary alluvial and terrace deposits. The shear-wave velocity profiles of the near-surface geologic units are used to characterize site classes according to the International Building Code [International Code Council, ICC. International Building Code. Structural and fire- and life-safety provisions (seismic, wind, accessibility, egress, occupancy and roof codes), 2006. Whittier, CA.] and the Turkish Seismic Code [Ministry of Public Works and Settlement, 1998. Turkish Seismic Code, Specification for Structures to be Built in Disaster Areas, Ankara, Turkey], and to develop a regional model for the average shear-wave velocity in the top 30 m. The resulting maps of site class indicate that the classification system for the Turkish Seismic Code results in a significant portion of the Ankara Basin being classified as Z4, the softest site class. The International Building Code site classification system results in most of the Ankara Basin being classified as D, stiff soil. These differences are caused by the Turkish Seismic Code incorporating information from only the surface layer, while the International Building Code incorporates information from the top 30 m.  相似文献   

Sedimentary archives of the French Atlantic coast (inner Bay of Vilaine,south Brittany): Depositional history and late Holocene climatic and environmental signals     

Philippe Sorrel  Bernadette Tessier  François Demory  Agnès Baltzer  Firas Bouaouina  Jean-Noël Proust  David Menier  Camille Traini 《Continental Shelf Research》2010,30(10-11):1250-1266

The late Holocene is of particular interest to our understanding of the evolution of coastal sedimentary systems because this period encompasses warmer and cooler periods, and rising sea level in northern Europe. Based on an approach combining AMS ¹⁴C, sedimentological and rock magnetic analyses on sediment cores complemented with seismic data collected in the macrotidal Bay of Vilaine (south Brittany), we document the depositional history of the inner bay coeval to the mid- to late-Holocene transgression in south Brittany. Correlation between sedimentary archives revealed the main sedimentary infilling phases during the last 6000 years. Four units (U1–U4) are recognized in the coastal sediment wedge of the system, corresponding to the stepwise marine invasion of the bay. We show that (1) marine inundation, due to the steep morphology of the bedrock, is diachronous between distal and proximal records. A time lag of ～1000 years is inferred over a distance of less than 5 km; (2) in the outer areas, the sedimentation has been condensed since 3000 years; (3) proximal estuarine archives offer the best record of sedimentary processes covering the last 2000 years, including the Medieval Warm Period (MWP).Correlations in proximal records in the Bay of Vilaine assess the connection between coastal sedimentary dynamics, climatic conditions and anthropogenic activities during the MWP. We match the preservation of clay deposits to increased river-borne suspended matter transported to the estuary probably as a result of accelerated land-use development (higher soil erosion) in the catchment area between ca. 880 and 1050 AD. Because the preservation of estuarine sedimentary successions is favoured when coastal wave sediment reworking is minimal, it is proposed that the prevailing climatic regime in south Brittany during the MWP likely resembled to that of the preferred negative phase of the North Atlantic Oscillation (NAO). Our data are fairly consistent with other late Holocene records from northern Europe including the Atlantic seaboard. However, they outline the difficulty in interpreting climatic and anthropogenic signatures in coastal sedimentary records where high-resolution chronologies required to unravel their respective influences are still missing.  相似文献   

Parametric analysis of liquid storage tanks base isolated by curved surface sliding bearings     

Emre Abalı  Eren Uçkan 《Soil Dynamics and Earthquake Engineering》2010,30(1-2):21-31

Curved surface sliding bearings, which are usually called as friction pendulum system (FPS) are commonly used for base isolation of liquid storage tanks since the period of the isolation system is independent of the storage level. However the restoring force and the damping at the isolation system are functions of axial load which changes during an earthquake excitation. This change might be in appreciable amounts especially for the tanks with high aspect ratios. The present paper focuses on earthquake performances of both broad and slender tanks base isolated by FPS bearings. The effects of overturning moment and vertical acceleration on axial load variation at the bearings are considered. The efficiency of the isolation system is investigated by analyzing the effects of various parameters such as; (i) isolation period, (ii) tank aspect ratio and (iii) coefficient of friction. The Haroun and Housner's three-degrees-of-freedom lumped mass model was used to solve the governing equations of motion in which convective, impulsive and rigid masses were included. A number of selected ground motions were considered and the results were compared to those of non-isolated cases.As a result, base isolation was found to be effective in reducing the base shear values for both broad and slender tanks without significantly affecting the sloshing displacements of the broad ones. The efficiency was even more pronounced for slender tanks subjected to near fault ground motions for isolation periods above 3 s. This specific value of isolation period also eliminated possible design problems arising from under-estimation of base shear values (up to 40%) due to ignoring the effects of axial load variation in lower isolation periods. Overturning effects should not be ignored especially for tanks with high aspect ratios (S) and being subjected to near fault ground motion.  相似文献   

Luminescence dating of Pleistocene alluvial sediments affected by the Alhama de Murcia fault (eastern Betics,Spain) – a comparison between OSL,IRSL and post‐IR IRSL ages     

Reza Sohbati  Andrew S. Murray  Jan‐Pieter Buylaert  Maria Ortuño  Pedro P. Cunha  Eulàlia Masana 《Boreas: An International Journal of Quaternary Research》2012,41(2):250-262

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