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81.
de Arruda Gomes Mayara Maria de Melo Verçosa Lívia Fragoso Cirilo José Almir 《Natural Hazards》2021,108(3):3121-3157
Natural Hazards - Floods are the most frequent natural disaster and pose a very challenging threat to many cities worldwide. Understanding the flood dynamic is essential for developing strategies... 相似文献
82.
内蒙古克什克腾旗长岭子斜长花岗斑岩位于大兴安岭锡林浩特增生杂岩带内。本文对长岭子斜长花岗斑岩进行了主微量元素地球化学以及锆石U?Pb年代学和Lu?Hf同位素研究。长岭子斜长花岗斑岩锆石206Pb/238U加权平均年龄为(248.1±4.7)Ma,是早三叠世岩浆活动的产物;继承锆石除外,样品中锆石具有正的εHf(t)值(5.78~12.41),二阶段模式年龄TDM2分别为914~488 Ma。长岭子斜长花岗斑岩具有较高的SiO2、Na2O和Al2O3含量以及较低的Fe2O3、MgO和CaO含量,属于偏铝质?过铝质的低钾?钙碱性系列I型花岗岩,富集Rb、K、U、Th、Pb、Sr等大离子亲石元素,亏损Nd、Ta、Ti等高场强元素。同时,斜长花岗斑岩具有高Sr低Y以及高Sr/Y比等特点,具有典型的埃达克质岩石特征,形成于加厚下地壳的部分熔融。综合上述地球化学特征,本文认为长岭子斜长花岗斑岩来源于加厚新生下地壳的部分熔融,表明早三叠世兴蒙地区并非岛弧的环境,而是处于碰撞造山环境,古亚洲洋在该时期已经闭合。 相似文献
83.
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
84.
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
85.
86.
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
87.
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
88.
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
89.
Jean-Franois Lnat Patrick Bachlery Alain Bonneville Pascal Tarits Jean-Louis Chemine Hugues Delorme 《Journal of Volcanology and Geothermal Research》1989,36(1-3)
On December 4, 1983 an eruption started at vents located 1.5 km southwest of the summit of Piton de la Fournaise at the base of the central cone. After 31 months of quiescence this was one of the longest repose period in the last fifty years. The eruption had two phases: December 4 to January 18 and January 18 to February 18. Phase 1 produced about 8 × 106 m3 of lava and Phase II about 9 × 106 m3. The erupted lava is an aphyric basalt whose mineralogical and geochemical composition is close to that of other lavas emitted since 1977.The precursors of the December 4 outbreak were limited to two-week shallow (1.5–3 km) seismic crisis of fewer than 50 events. No long-term increase was noted in the local seismicity which is very quiet during repose periods and no long-term ground inflation preceded the eruption. Outbreaks of Phases I and II were preceded by short (2.5 hours and 1.5 hours) seismic swarms corresponding to the rise of magma toward the surface from a shallow reservoir. Large ground deformation explained by the emplacement of the shallow intrusions, was recorded during the seismic swarms. A summit inflation was observed in early January, before the phase II outbreak, while the phase I eruption was still continuing.Piton de la Fournaise volcanological observatory was installed in 1980. Seismic and ground deformation data now available for a period of 4 years including the 1981 and the 1983–1984 eruptions, allow us to describe the physical behavior of the volcano during this period. These observations lead us to propose that the magma transfer from deep levels to the shallow magma reservoir is not a continuous process but a periodic one and that the shallow magma reservoir was not resupplied before the 1981 and 1983–1984 eruptions. Considerations on the eruptive history and the composition of recent lavas indicate that the reservoir was refilled in 1977. 相似文献
90.
Patrice Lerebour J.Philippe Ranon Thierry Aug 《Journal of Volcanology and Geothermal Research》1989,36(1-3)
The Grand Brûlé borehole intersects a thick pile of basaltic lavas, down to 1010 m, and a basic-ultrabasic intrusive complex, from 1010 to 3003.50 m.The lavas are, in general, unaltered except in two fractured zones, where hydrothermal fluids circulated at temperatures not exceeding 350 ° C. The main secondary minerals there are pyroxene, feldspar, epidote, actinolite and chlorite.The entire thickness of the intrusive body intersected contains secondary minerals representing three stages of cooling:
- 1. 1. A late magmatic episode (600–900°C) characterized by biotite, kaersutite, edenite and pargasite.
- 2. 2. A hydrothermal episode (T<- 350°C) characterized by epidote, albite, biotite, actinolite and chlorite.
- 3. 3. A phase of serpentinization (T≤ 350°C).