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81.
Mustafa Al-Marzooq Mamadou S. Diallo Vincent Etienne Thierry Tonellot SanLinn I. Kaka 《Geophysical Prospecting》2019,67(7):1825-1837
The Rub Al Khali region in Saudi Arabia is characterized by the presence of sand dunes separated by salt flats, also called Sabkhas. In general, the elevation of dunes in this region varies between 90 and 250 m above sea level. The presence of these sand dunes, along with the rapidly changing surface topography poses challenges for seismic data acquisition and processing. The high contrast in acoustic impedance between the dune base and the underlying formation often results in amplification of seismic waves that are recorded at stations located on the surface of sand dunes. Attempts to address the issue using conventional surface-consistent amplitude scaling methods without reducing these amplification effects generally fail, thus compromising the suitability of the processed data for amplitude versus offset analysis. In this study, we propose a new reference site technique to reduce the effects of sand dune amplification, enabling the production of data sets that are suitable for amplitude versus offset processing. The proposed technique uses a deterministic approach to derive surface-consistent, frequency-dependent de-amplification functions for shots and stations located on the dunes only. Two-dimensional synthetic and field data examples show that the technique significantly reduces the effects of sand dune amplification. 相似文献
82.
The Xiadian Fault is a very important concealed active fault in the Beijing Plain. It is the seismogenic fault of the Sanhe-Pinggu MS8.0 earthquake in 1679. The ancient earthquake sequence in the long historical period is of great significance to understand accurately the activity characteristics of the fault and effectively reduce the earthquake disaster risk in Beijing. We have re-interpreted the Dahuzhuang trench, and identified three layers of buried paleosol, six collapsed wedges and one sand liquefaction event. Further, through the comparison with the landmark strata and paleo-earthquake events revealed by other trenches on the fault, an ancient earthquake sequence with a long historical period of the Xiadian Fault was established:since the 31ka, the Xiadian Fault has 11 occurrences of earthquake events (including the 1679 earthquake), and the average recurrence interval is about 2.8ka. The paleo-seismic sequence also shows that there is an ancient earthquake cluster period from 25ka to 15ka, and there are 5 strong earthquakes in the cluster period. The average recurrence interval is about 2.0ka, which reflects the phase difference of the Xiadian Fault activity. 相似文献
83.
研究源-汇系统对于理解岩石风化、河流输砂、泥砂沉积以及陆地和海洋沉积过程具有重要意义。我国江苏省东海岸具有丰富的沉积物供应,在某些沿海地段形成了一系列沙脊,是进行沉积物源-汇过程研究的理想沉积记录之一。但目前对其物源区来自哪里还未达成共识。我们利用已发表的碎屑锆石U-Pb年龄和钾长石Pb同位素数据,结合江苏沙脊及其周缘区域的数据结果,详细厘定江苏沙脊的物源区,并运用蒙特卡罗反演模型定量评估江苏沙脊潜在物源区对其物质贡献率。结果表明江苏沙脊北部的碎屑物质主要受大别山(45%)和鲁中山区(24%)的共同影响;黄河(29%)、古黄河(27%)和长江(25%)的碎屑物质对江苏沙脊中部的物质组成起重要影响。江苏沙脊南部的物源主要来自长江(68%)。江苏沙脊的出现得益于黄河和长江这样的大陆尺度的大河搬运了丰富的碎屑物质到下游,南黄海西海岸的平坦地貌有利于保存这些碎屑物质,末次冰期后东亚陆架海动力过程(潮汐、海浪和沿岸流等)持续对其改造,这体现了河流-海洋在塑造河口-海岸地貌中的交互作用。 相似文献
84.
A series of 1 g model tests was conducted to investigate the accumulated vertical pullout displacement and unloading stiffness of bucket foundations embedded in dry and saturated sands. The foundations were subjected to vertical pullout cyclic loading with different load amplitudes. Cyclic load was applied up to 104 cycles. Test results showed that the accumulated vertical pullout displacement increased with the increase in the number of load cycles and cyclic load amplitudes. The unloading stiffness of the bucket foundations decreased with the increase in load amplitude and number of cycles. Empirical equations were proposed based on the test results to evaluate the accumulated vertical pullout displacement and unloading stiffness of the bucket foundations in saturated sand. These equations can be used for the preliminary design of single or tripod bucket foundations. 相似文献
85.
水电站坝的砂层地基地震液化可靠度研究 总被引:2,自引:1,他引:1
对四川地区江河上数座水电站坝基砂层的26组动力三轴试验资料进行了统计分析,基于动剪应力比法的液化判别方法推导了的地震液化的极限状态方程,使用蒙特卡洛随机抽样的方法计算了砂层液化的失效概率,并对某水电站的厂房地基砂层的液化可靠度进行了计算分析。研究表明,统计按粉砂样总体和中细砂样总体划分较为合理;砂层的动剪应力比可采用正态分布;电站砂层地基地震液化的最危险工况为,闸坝盖重加稳定的向上渗流及遭遇Ⅶ度地震荷载,为高液化风险,其液化概率随埋深加大而增大,最危险部位为砂层底板,对坝基砂层应进行抗液化处理。 相似文献
86.
87.
Estimation of areas of sand and dust emission in the Hexi Corridor from a land cover database: an approach that combines remote sensing with GIS 总被引:1,自引:0,他引:1
The present study combined remote sensing with geographical information system (GIS) technology to interpret Landsat TM images
from 1996 to 2000 and establish a land cover database for the Hexi Corridor of China’s Gansu Province. The areas of sand and
dust emission and trends in their change were extracted by analyzing the database, with the following results: In 2000, the
source area for sand and dust storms totaled nearly 170,000 km2, accounting for 75.1% of the study region. The emission area decreases from as much as 70,000 km2 in winter and spring to around 58,000 km2 in summer and autumn, accounting for 41.1 and 34.1% of the source area, respectively. During the 4 years of the study period,
the emission area decreased by nearly 57 km2 in winter and spring (a 0.1% change); however, the vulnerability of the land surface to wind erosion increased in ca. 190 km2 and decreased in ca. 102 km2. Although the area of dust emission decreased from 1996 to 2000, the area vulnerable to wind erosion increased by ca. 87 km2, and the increased number of sand and dust storm days in the region between 2000 and 2003 appears to be correlated with this
increase. 相似文献
88.
In this paper, a modeling procedure is carried out to numerically analyze the end bearing capacity of drilled shafts in sand.
The Mohr–Coulomb elastic plastic constitutive law with stress dependent elastic parameters is used for all numerical analyses
performed in this study. The numerical results are compared with the available experimental equations. It is seen that numerical
results are in good agreement with experimental equations. The variation of the end bearing capacity of drilled shafts versus
embedment depth is also studied. Numerical results show that with increase in pile embedment depth, the end bearing capacity
increases. However, the rate of increase becomes smaller as the pile embedment depth increases. Also, numerical analyses show
that, for equal settlement, the end bearing decreases with increase in the pile diameter. Finally, a sensitivity analysis
is performed to obtain the separate effect of each sand parameter on the end bearing capacity of drilled shafts, and the parameters
that are most influential are identified. 相似文献
89.
Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations. 相似文献
90.
This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke.A series of experiments are conducted with different types of sedime... 相似文献