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901.
对等辐照方位与建筑朝向的选择 总被引:3,自引:0,他引:3
本文计算并分析了墙面可照时间和天文辐射日总量及其随坡向的分布,从中发现,存在东西对称的方位,在该方位上墙面的可照时间或天文辐射日总量在冬夏半年各自对应的太阳赤纬时都相等,称之为对等日照方位和对等辐射方位,统称为对等辐照方位,并且,在对等辐照方位以南的各方位上冬半年的可照时间(天文辐射日总量)大于夏半年对应太阳赤纬时的值,而对等辐照方位以北各方位的情况相反,因而对等辐照方位可作为适宜建筑朝向选择的临 相似文献
902.
A. Castro C. Fernández H. El-Hmidi M. El-Biad M. Díaz J. de la Rosa F. Stuart 《International Journal of Earth Sciences》1999,88(1):26-37
The Aracena metamorphic belt (AMB), southwest Iberian peninsula, is characterized by the following geological elements: (a)
a high-temperature/low-pressure (HT/LP) metamorphic belt a few kilometres wide and more than 200 km long; (b) a linear belt
of oceanic amphibolites with a low-pressure inverted metamorphic gradient; (c) crustal-scale ductile shear zones; and (d)
mafic, noritic intrusions of high-Mg andesite (boninite) composition. The relationships between these elements led to the
proposal of a model of ridge subduction for this sector of the Hercynian belt of Europe. This interpretation is supported
by the age relationships displayed between the main rock units considered representative of the main tectonic and petrological
processes responsible for the geological elements mentioned previously. The results of a geochronological study (Ar–Ar, Rb–Sr
and Sm–Nd) clearly support a Late Paleozoic tectonic evolution at an active continental margin. The time evolution of the
metamorphism in the oceanic domain, ranging from 342.6±0.6 Ma in the west to 328.4±1.2 Ma in the east, over a distance of
70 km along the metamorphic belt, support a tectonic model of triple-junction migration responsible for the creation at depth
of a slab-free window with decisive consequences for the thermal evolution of the region. The origin of the linear metamorphic
belt of HT/LP regime may be explained by the migration along a continental margin of a punctual thermal anomaly induced by
the creation of a triple-junction at the continental margin.
Received: 9 March 1998 / Accepted: 9 December 1998 相似文献
903.
河北山前平原地下水^32Si年龄初探 总被引:6,自引:3,他引:3
^32Si是放射性同位素,半衰期约140a可以测定50~1000a地下水的年龄,本文用Fe(OH)3共沉淀法从天然水中提取SiO2回收率可达30%~98%,然后提取和纯化^32P,将H3PO4溶液和Pico-flour^TMLLT混合制备计数溶液,用液体闪烁计数法测量中^32P的放射性,本底计数为4.80cph,仪器效率为45.34%,然后用公式计算样品的^32Si放射性浓度和地下水的^32Si年 相似文献
904.
Field estimate of paleoseismic slip on a normal fault using the Schmidt hammer and terrestrial LiDAR: Methods and application to the Hebgen fault (Montana,USA) 下载免费PDF全文
The weathering characteristics of bedrock fault scarps provide relative age constraints that can be used to determine fault displacements. Here, we report Schmidt hammer rebound values (R‐values) for a limestone fault scarp that was last exposed in the 1959 Mw 7.3 Hebgen Lake, Montana earthquake. Results show that some R‐value indices, related to the difference between minimum and maximum R‐values in repeated impacts at a point, increase upward along the scarp, which we propose is due to progressive exposure of the scarp in earthquakes. An objective method is developed for fitting slip histories to the Schmidt hammer data and produces the best model fit (using the Bayesian Information Criterion) of three earthquakes with single event displacements of ≥ 1.20 m, 3.75 m, and c. 4.80 m. The same fitting method is also applied to new terrestrial LiDAR data of the scarp, though the LiDAR results may be more influenced by macro‐scale structure of the outcrop than by differential weathering. We suggest the use of this fitting procedure to define single event displacements on other bedrock fault scarps using other dating techniques. Our preliminary findings demonstrate that the Schmidt hammer, combined with other methods, may provide useful constraints on single event displacements on exposed bedrock fault scarps. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
905.
COSMOGENIC NUCLIDES EXPOSURE DATING FOR BEDROCK FAULT SCARP: RECONSTRUCTING THE PALEOEARTHQUAKE SEQUENCE 总被引:1,自引:0,他引:1 下载免费PDF全文
ZHANG Jin-yu ZENG Jing WANG Heng SHI Xu-hua YAO Wen-qian XU Jing XU Xin-yue 《地震地质》2018,40(5):1149-1169
The bedrock scarps are believed to have recorded the continuous information on displacement accumulation and sequence of large earthquakes. The occurrence timing of large earthquakes is believed to be correlated positively with the exposure duration of bedrock fault surfaces. Accordingly, cosmogenic nuclides concentration determined for the bedrock footwall can offer their times, ages, and slip over long time. In general, multiple sites of fault scarps along one or even more faults are selected to carry out cosmogenic nuclide dating in an attempt to derive the temporal and spatial pattern of fault activity. This may contribute to explore whether earthquake occurrence exhibits any regularity and predict the timing and magnitude of strong earthquakes in the near future. Cosmogenic nuclide 36 Cl dating is widely applied to fault scarp of limestone, and the height of fault scarp can reach as high as 15~20m. It is strongly suggested to make sure the bedrock scarp is exhumed by large earthquake events instead of geomorphic processes, based on field observation, and data acquired by terrestrial LiDAR and ground penetration radar (GPR). In addition, it is better for the fault surface to be straight and fresh with striations indicating recent fault movement. A series of bedrock samples are collected from the footwall in parallel to the direction of fault movement both above and below the colluvium, and each of them is~15cm long,~10cm wide, and~3cm thick. The concentrations of both cosmogenic nuclide 36 Cl and REE-Y determined from these samples vary with the heights in parallel to fault scarps. Accordingly, we identify the times of past large earthquakes, model the profile of 36 Cl concentration to seek the most realistic one, and determine the ages and slip of each earthquake event with the errors. In general, the errors for the numbers, ages, and slips of past earthquake events are ±1-2, no more than ±0.5-1.0ka, and ±0.25m, respectively. 相似文献
906.
Perturbation of fluvial sediment fluxes following the 2008 Wenchuan earthquake 总被引:1,自引:0,他引:1 下载免费PDF全文
Wei Wang Vincent Godard Jing Liu‐Zeng Dirk Scherler Chong Xu Jinyu Zhang Kejia Xie Olivier Bellier Claire Ansberque Julia de Sigoyer ASTER Team 《地球表面变化过程与地形》2017,42(15):2611-2622
Quantifying the removal of co‐seismic landslide material after a large‐magnitude earthquake is central to our understanding of geomorphic recovery from seismic events and the topographic evolution of tectonically active mountain ranges. In order to gain more insight into the fluvial erosion response to co‐seismic landslides, we focus on the sediment fluxes of rivers flowing through the rupture zone of the 2008 Mw 7.9 Wenchuan earthquake in the Longmen Shan of the eastern Tibetan Plateau. Over the post‐seismic period of 2008–2013, we annually collected river sediment samples (0.25–1 mm) at 19 locations and measured the concentration of cosmogenic 10Be in quartz. When compared with published pre‐earthquake data, the 10Be concentrations declined dramatically after the earthquake at all sampling sites, but with significant spatial differences in the amplitude of this decrease, and were starting to increase toward pre‐earthquake level in several basins over the 5‐year survey. Our analysis shows that the amplitude of 10Be decrease is controlled by the amount of landslides directly connected to the river network. Calculations based on 10Be mixing budgets indicate that the sediment flux of the 0.25–1 mm size fraction increased up to sixfold following the Wenchuan earthquake. Our results also suggest that fluvial erosion became supply limited shortly after the earthquake, and predict that it could take a few years to several decades for fluvial sediment fluxes to go back to pre‐earthquake characteristics, depending on catchment properties. We also estimate that it will take at least decades and possibly up to thousands of years to remove the co‐seismic landslide materials from the catchments in the Longmen Shan. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
907.
Spatial and temporal replicability of meteoric and in situ 10Be concentrations in fluvial sediment 下载免费PDF全文
Veronica Sosa Gonzalez Amanda H. Schmidt Paul R. Bierman Dylan H. Rood 《地球表面变化过程与地形》2017,42(15):2570-2584
Cosmogenic isotopes, short‐lived radionuclides, elemental concentrations and thermochronometric indicators are measured in river sand to quantify erosion rates and trace sediment sources, and/or infer erosional processes. Interpretations of detrital sediment analyses are often based on the rarely tested assumption of time‐invariant tracer concentration. A better understanding of when and where this assumption breaks down and what sampling strategies minimize temporal and small‐scale spatial variance will improve science done using detrital river sediment. Here, we present new and previously published spatial and temporal replicates measured for in situ and meteoric 10Be (10Bei and 10Bem, respectively). Our new data include 113 replicate pairs, taken from agricultural and/or tectonically active watersheds in China months to millennia apart and spatial replicates taken up to 2 km apart on the same day. The mean percentage difference is 10% (?122% to 150%) for both systems considered together; the mode is close to 0% for both systems; and 36% of pairs of samples replicate within our analytical accuracy at 2σ . We find that 10Bei replicates better than 10Bem (p < 0.01). 10Bei replicability is worse in steeper basins, suggesting that stochastic processes (i.e. landslides) affect reproducibility. 10Bem replicability is worse in larger basins, suggesting non‐conservative behavior of 10Bem as sediment moves downstream. Our results are consistent with the few previously published replicate studies. Considering all replicate data in a wide range of landscapes, in areas with deep erosional processes, replicability is poor; in other areas, replicability is good. This suggests that, in steep, tectonically active, and/or agricultural landscapes, individual detrital sediment measurements do not represent upstream rates as well as larger populations of samples. To ensure that measurements are representative of the upstream watershed, our data suggest that samples be amalgamated either over time or from several places close by in the same channel. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
908.
There are many examples of exposed or buried rock surfaces whose age is of interest to geologists and archaeologists. Luminescence dating is a well-established method of absolute chronology which has been successfully applied to a wide range of fine-grained sediments from hundreds of years to several hundred thousand years. Optical stimulated luminescence (OSL) has been recently proposed as a new method to date these rock surfaces (Laskariset al., 2011; Sohbatiet al., 2012a; Chapotet al., 2012; Pedersonet al., 2014; Sohbatiet al., 2015; Freieslebenet al., 2015). The basic principle is that luminescence signal of rock surface will soon decay when the rock is exposed to sunlight. When the rock surface is turned to be buried side, the OSL signal begins to accumulate again. With the variation of residual luminescence with depth, it is possible to estimate exposure and burial history of the rock. This article describes briefly the different luminescence dating methods for rock surfaces, its progress, application examples and present problems. For instance, Sohbatiet al. (2011) studied the depth dependence of the bleaching of the IRSL signal from granitic rocks, Laskaris and Liritzis (2011) proposed a mathematical function to describe the attenuation of daylight into rock surfaces, Sohbatiet al. (2012a) developed their model to include the environmental dose rate, Sohbatiet al. (2012b) overcame the problem of parameter estimation by using a known-age road-cut sample for calibration, Sohbatiet al. (2012c) further developed the OSL surface exposure dating model by including the simultaneous effect of daylight bleaching and environmental dose rate, and so on. These studies indicate that OSL dating method for rock surface can be applied widely to studies of geological and geomorphological evolution, archeology and Quaternary tectonic activity. 相似文献
909.
Soil formation and weathering in a permafrost environment of the Swiss Alps: a multi‐parameter and non‐steady‐state approach 下载免费PDF全文
Barbara Zollinger Christine Alewell Christof Kneisel Dagmar Brandová Marta Petrillo Michael Plötze Marcus Christl Markus Egli 《地球表面变化过程与地形》2017,42(5):814-835
Spatially discontinuous permafrost conditions frequently occur in the European Alps. How soils under such conditions have evolved and how they may react to climate warming is largely unknown. This study focuses on the comparison of nearby soils that are characterised by the presence or absence of permafrost (active‐layer thickness: 2–3 m) in the alpine (tundra) and subalpine (forest) range of the Eastern Swiss Alps using a multi‐method (geochemical and mineralogical) approach. Moreover, a new non‐steady‐state concept was applied to determine rates of chemical weathering, soil erosion, soil formation, soil denudation, and soil production. Long‐term chemical weathering rates, soil formation and erosion rates were assessed by using immobile elements, fine‐earth stocks and meteoric 10Be. In addition, the weathering index (K + Ca)/Ti, the amount of Fe‐ and Al‐oxyhydroxides and clay minerals characteristics were considered. All methods indicated that the differences between permafrost‐affected and non‐permafrost‐affected soils were small. Furthermore, the soils did not uniformly differ in their weathering behaviour. A tendency towards less intense weathering in soils that were affected by permafrost was noted: at most sites, weathering rates, the proportion of oxyhydroxides and the weathering stage of clay minerals were lower in permafrost soils. In part, erosion rates were higher at the permafrost sites and accounted for 79–97% of the denudation rates. In general, soil formation rates (8.8–86.7 t/km2/yr) were in the expected range for Alpine soils. Independent of permafrost conditions, it seems that the local microenvironment (particularly vegetation and subsequently soil organic matter) has strongly influenced denudation rates. As the climate has varied since the beginning of soil evolution, the conditions for soil formation and weathering were not stable over time. Soil evolution in high Alpine settings is complex owing to, among others, spatio‐temporal variations of permafrost conditions and thus climate. This makes predictions of future behaviour very difficult. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
910.
R. Grischott F. Kober M. Lupker K. Hippe S. Ivy‐Ochs I. Hajdas B. Salcher M. Christl 《地球表面变化过程与地形》2017,42(7):1065-1077
Terrestrial cosmogenic nuclides (TCN) have widely been used as proxies in determining denudation rates in catchments. Most studies were limited to samples from modern active streams, thus little is known about the magnitude and causes of TCN variability on millennial time scales. In this work we present a 6 kyrs long, high resolution record of 10Be concentrations (n = 18), which were measured in sediment cores from an alluvial fan delta at the outlet of the Fedoz Valley in the Swiss Alps. This record is paired with a 3‐year time series (n = 4) of 10Be measured in sediment from the active stream currently feeding this fan delta. The temporal trend in the 10Be concentrations after correction for postdepositional production of 10Be was found to be overall constant and in good agreement with the modern river 10Be concentration. The calculated mean catchment‐wide denudation rate amounts to 0.73 ± 0.18 mm yr?1. This fairly constant level of 10Be concentrations can be caused by a constant denudation rate over time within the catchment or alternatively by a buffered signal. In this contribution we suggest that the large alluvial floodplain in the Fedoz Valley may act as an efficient buffer on Holocene time scales in which sediments with different 10Be signatures are mixed. Therefore, presumable variations in the 10Be signals derived from changes in denudation under a fluctuating Holocene climate are only poorly transferred to the catchment outlet and not recorded in the 10Be record. However, despite the absence of high frequency signals, we propose that the buffered and averaged 10Be signal could be meaningfully and faithfully interpreted in terms of long‐term catchment‐averaged denudation rate. Our study suggests that alluvial buffers play an important role in regulating the 10Be signal exported by some alpine settings that needs to be taken into account and further investigated. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献