An empirical spectral ground-motion model for Iran

A new ground-motion prediction equation for 5%-damped horizontal spectral acceleration applicable to Iran is presented. On the basis of analysis of variance (ANOVA), selected West-Eurasian records are added to an existing dataset of Iranian accelerometric data to yield a ground-motion prediction equation applicable at wider ranges of magnitude and distance. The advantages of using this model rather than those proposed previously for Iran are discussed by considering the distribution of residuals against the explanatory variables, magnitude and distance. The applicability of the proposed model, as well as those of several other models developed for shallow crustal environments, is also investigated by means of statistical tools. The results reveal the overall suitability of the new model as well as the validity of models developed using mainly Eurasian strong-motion records. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Spatio-temporal variability of surface soil water content and its influencing factors in a desert area,China

Abstract

Knowledge of the variability of soil water content (SWC) in space and time plays a key role in hydrological and climatic modelling. However, limited attention has been given to arid regions. The focus of this study was to investigate the spatio-temporal variability of surface soil (0–6 cm) water content and to identify its controlling factors in a region of the Gobi Desert (40 km²). The standard deviation of SWC decreased logarithmically as mean water content decreased, and the coefficient of variation of SWC exhibited a convex upward pattern. The spatial variability of SWC also increased with the size of the investigated area. The spatial dependence of SWC changed over time, with stronger patterns of spatial organization in drier and wetter conditions of soil wetness and stochastic patterns in moderate soil water conditions. The dominant factors regulating the variability of SWC changed from combinations of soil and topographical properties (bulk density, clay content and relative elevation) in wet conditions to combinations of soil and vegetation properties (bulk density, clay content and shrub coverage) in dry conditions. This study has important implications for the assessment of soil quality and the sustainability of land management in arid regions.     

Assessing the impacts of microtopography on soil erosion under simulated rainfall,using a multifractal approach

This study aimed to investigate the changing characteristics of microrelief of purple soil and its erosional response during successive stages of water erosion, including splash erosion, sheet erosion, and rill erosion. Methods employed included a rainfall simulator and the use of a laser scanner to generate a digital elevation model. Three artificial tillage practices, including conventional tillage (CT), artificial digging (AD), and ridge tillage (RT), were used to simulate different microrelief patterns. Eighteen artificial rainfall experiments were conducted using three 2 × 1 m boxes with a rainfall intensity of 1.5 mm min^?1 on a 15° slope. The results showed that the soil roughness (SR) index values for the tillage slopes were RT > AD > CT. The combined effects of detachment by raindrop impact and transport by run‐off decreased the SR index, whereas rill erosion increased the SR index during rainfall event. Microtopography and drainage networks have strong multifractal behaviours. The multifractal parameters of microtopography reflect the overall characteristics as well as the characteristics of the local soil surface. Within a certain range of threshold values, higher microrelief causes less soil erosion. However, when the parameters of spatial heterogeneity of microtopography exceed the threshold values, a higher degree of microrelief can increase soil erosion. These results help clarify the effect of microtopography on soil erosion and provide a theoretical foundation to guide future tillage practices on sloping farmland of purple soil.     

二阶同步挤压S变换及其在地震谱分解中的应用

同步挤压S变换是一种处理非平稳信号的新时频变换方法,通过"挤压"信号的S变换结果,可以得到高分辨率的时频谱.但是,当信号的相位随时间呈非线性变化时,同步挤压S变换计算出的瞬时频率会出现误差,并造成时频谱分辨率降低.为了改善其对于该类信号的时频分析效果,我们利用时间和频率的二阶偏导数对瞬时频率计算式进行修正,提出二阶同步挤压S变换.合成信号处理结果表明,二阶同步挤压S变换的分辨率不但明显高于常用时频变换,在信号瞬时频率随时间呈二次或正弦变化的情况下,其时频挤压效果也好于同步挤压S变换.我们将二阶同步挤压S变换应用到天然气地震勘探资料的谱分解当中,结果表明,二阶同步挤压S变换可以很好地检测到与天然气相关的谱异常.因此,二阶同步挤压变换对于地震解释是一种很有潜力的方法.     

垂直重力梯度反演Moho面的频谱域公式及其应用

通过求解引力相等原则下的Fredholm积分方程,可以得到不规则单一密度界面(Moho面)的起伏.本文充分参考了前人的理论研究,推导出扰动垂直重力梯度确定Moho面深度的频谱域表达式,该式具有二次项迭代精度.运用此公式进行了全球Moho面的恢复计算,并将该结果与CRUST1.0模型和GEMMA Moho模型进行了对比和验证.     

Time series analysis using spectral techniques: Oscillatory currents

The use of time domain and frequency domain techniques in the analysis of geomorphological time series is discussed and the techniques of spectral analysis are introduced. An Excel worksheet is used to analyse wave-current data from Slapton Sands in Devon and the advantages and limitations of the technique are listed.     

Spatial explicit soil moisture analysis: pattern and its stability at small catchment scale in the loess hilly region of China

Soil moisture is essential for plant growth and terrestrial ecosystems, especially in arid and semi‐arid regions. This study aims to quantify the variation of soil moisture content and its spatial pattern as well as the influencing factors. The experiment is conducted in a small catchment named Yangjuangou in the loess hilly region of China. Soil moisture to a depth of 1 m has been obtained by in situ sampling at 149 sites with different vegetation types before and after the rainy season. Elevation, slope position, slope aspect, slope gradient and vegetation properties are investigated synchronously. With the rainy season coming, soil moisture content increases and then reaches the highest value after the rainy season. Fluctuation range and standard deviation of soil moisture decrease after a 4‐month rainy season. Standard deviation of soil moisture increases with depth before the rainy season; after the rainy season, it decreases within the 0‐ to 40‐cm soil depth but then increases with depths below 40 cm. The stability of the soil moisture pattern at the small catchment scale increases with depth. The geographical position determines the framework of soil moisture pattern. Soil moisture content with different land‐use types is significantly increased after the rainy season, but the variances of land‐use types are significantly different. Landform and land‐use types can explain most of the soil moisture spatial variations. Soil moisture at all sample sites increases after the rainy season, but the spatial patterns of soil moisture are not significantly changed and display temporal stability despite the influence of the rainy season. Copyright © 2013 John Wiley & Sons, Ltd.     

On the spectral peaks of volcanic tremor at Stromboli

Seismic activity at Stromboli Volcano is characterized by a variety of signals, emanating from three vents. For a long time, the northwest vent has been in constant activity. Periodically, large explosions occur and material is ejected beyond the crater walls. These large explosions are accompanied by sonic and infrasonic pressure waves in the atmosphere, and explosion quakes. Apart from large explosions, there is constant activity in the form of continuous gas bursts which are related to low infrasonic pulses in the atmosphere and volcanic tremor. We assume that volcanic tremor and low pressure infrasonics are generated by gas bubbles inside the volcanic conduit, and accordingly, we compute synthetic tremor by modeling the source function as a pressure variation in a spherical cavity that propagates through a finely layered medium, by means of Haskell's formalism. To simulate a tremor, we superpose in time domain a large number of such pulses of varying amplitudes and time delays, according to the observed infrasonic series. In addition to the spectral similarity, the observed and synthetic tremor display the same autocorrelation and Hurst exponents, implying similar long-term correlation. We present strong evidence in favour of an interpretation of the spectral peaks of the volcanic tremor at Stromboli in terms of resonances of the layered structure, hence, as a path effect rather than a source effect.     

天津地区覆盖层土动力学参数统计分析

收集天津地区近年来有代表性的具有完整土动力学参数作为实验数据的地震安全性评价报告66份,用两种统计方法按不同深度统计分析粉质黏土、黏土、粉土、砂土、淤泥质土等的实测土动力学参数,给出动剪切模量比和阻尼比平均值。选取2个典型工程场地,构建土层分析模型,进行土层地震反应分析计算。结果表明,本文得到的统计2值在天津地区具有一定的代表性和适用性,与实测值结果更为接近。对于获得原状土样困难的场地,特别是对于较薄的夹层土,可参照统计2结果进行分析计算。     

Microtopography,water storage and flow patterns in a fine‐textured soil under agricultural use

Agricultural use of soils implies tillage and often compaction and therefore influences processes on soil surface and affects infiltration of water into the subsoil. Although many studies on soil surface processes or flow patterns in soils exist, works relating both are rare in literature. We did two tracer experiments with Brilliant Blue FCF on a tilled and compacted plot and a non‐tilled one to investigate water storage on the soil surface during simulated rainfall and changes of soil microtopography, to analyse the associated flow patterns in the soil and to relate both to tillage and compaction. Our results show that storage was larger on the tilled and compacted plot than on the non‐tilled one. After tillage, transport processes above the plough pan were partly disconnected from those underneath because macropores were disrupted and buried by the tillage operation. However, preferential flow along cracks occurred on both plots and the macropores buried below the tillage pan still functioned as preferential flow paths. Therefore, we conclude that the studied soil is susceptible to deep vertical solute propagation at dry conditions when cracks are open, irrespective of tillage and compaction. Copyright © 2012 John Wiley & Sons, Ltd.     

Sensitivity of Mesoscale Surface Dynamics to Surface Soil and Vegetation Contrasts over the Carolina Sandhills

A region of contrasting soils exists over the Carolinas region of the southeastern United States. Previous research has shown an increase in mesoscale summertime precipitation over this region. Numerical simulations are analyzed to investigate the relationships between mesoscale surface dynamics and the transition from clay to sandy soils over this region. Numerical modeling experiments using four different soil and vegetation patterns suggest that the presence of the clay-to-sand transition zone produces a surface heat flux gradient and enhanced convergence. The soil contrasts appear to dominate over vegetation contrasts in affecting local surface heating and convergence in the model atmosphere.     

中硬场地下两种土层地震反应方法与精确解的对比

基于谐波入射下的波动理论频域精确解,导出线性时域精确解,并在Matlab环境中编制相应的计算程序;选取8个简化的中硬场地剖面,用LSSRLI-1、精确解和SHAKE2000三种方法计算各场地在不同输入条件下的地震反应。结果表明:程序计算所得地表反应谱和土体剪应变分布与SHAKE2000结果一致;LSSRLI-1方法得到的地表反应谱与前二者结果一致;LSSRLI-1方法在某些情况下得到的土体剪应变分布与另外二者结果存在较大偏差,该偏差对地表反应谱有着不可忽略甚至非常显著的影响。     

Identification of phase propagation of water level in tidal river by spectral analysis

 Water levels of the five river stages in the Taipei Basin are analyzed by using spectral analysis in time-frequency domain through one-year hourly data. The autospectral and cross-spectral density function, coherence, phase angle and associated statistic parameters are studied. The semi-diurnal, diurnal and quarter-diurnal tidal components are significant for river stages, which are also apparently related to astronomical tides of M₂, S₂, N₂, S₁, O₁ and M₄, MK₄ or MS₄ respectively. The time lags versus propagation distance are shown as linear distribution for two stream systems. The time lags are 3.2, 4.0 and 2.5 (h) for semi-diurnal, diurnal and quarter-diurnal components in Tanshui River – Tanhan Stream system, while 3.5, 3.5 and 2.2 (h) in Tanshui River – Hsintien Stream system. This research was supported by the Institute of Nuclear Energy Research(INER), Atomic Energy Council, Taiwan, Republic of China, under the fund of the Executive Yuan. The author appreciates Taiwan Provincial Government Water Resources Department and Central Weather Bureau for providing useful data.     

基于谱元法的全波形反演及其在海底地震数据中的应用

全波形反演已被广泛应用于获取地下速度结构.而反演问题与正演方法密切联系,针对特定反演问题,合适的正演方法能极大提高反演效率和精度.本文首先验证谱元法在含起伏界面模型数值模拟方面的优势,在此基础上将谱元法作为正演引擎应用于全波形反演,并为克服未知子波的影响,采用一种归一化的频率域目标泛函.结果表明,起伏地表情况下,基于谱元法的全波形反演相比于基于传统有限差分法反演,具有更高的反演精度.进一步,本文将基于谱元法的波形反演方法应用于OBS观测系统的理论合成数据和野外采集数据.谱元法非结构化网格剖分自然满足自由边界条件,能很好地适应不规则海床并模拟多次波.理论实验表明,即使在OBS观测系统很稀疏的情况下,基于谱元法的全波形反演仍能获得海底以下正确的高波数速度结构.在处理实际OBS数据时,本文采用分频策略以减少反演非线性,初始模型成功更新,其结果揭示了西沙海槽海底以下更多的细节信息.

     

博斯腾湖表层沉积物无机碳及其稳定同位素空间异质性

2012年8月,在新疆博斯腾湖13个站点进行表层沉积物采集,分析无机碳及其碳、氧稳定同位素的含量和空间分布特征,探讨该湖表层沉积物无机碳(TIC)的空间变化影响因素.结果表明:2012年,博斯腾湖表层沉积物TIC含量平均值为5.5%,变幅为3.8%~9.8%,而δ13Ccarb和δ18Ocarb平均值分别为0.71‰和-4.4‰,范围为-0.23‰~2.27‰和-5.53‰~-2.55‰.从空间来看,湖泊北岸TIC值明显高于南岸,最高值出现在湖泊西北部的黄水沟水域,而河口区和湖心区最低.总体上,博斯腾湖表层沉积物TIC主要是湖泊自生的,其空间分布主要受开都河、黄水沟等入湖河水的影响,导致水体矿化度和营养盐的空间差异,进而影响了碳酸盐的析出与沉淀.另外,湖泊局部的水动力条件也影响TIC的保存与分布.δ13Ccarb与δ18Ocarb的极显著正相关说明近几年博斯腾湖封闭程度较好,尤其是东部大湖区,属于封闭环境碳酸盐沉淀.     

Modelling the spatial variation in soil moisture at the landscape scale: an application to five areas of ecological interest in the UK

A simple conceptual hydrological model that explicitly includes the lateral movement of soil water and operates efficiently at the landscape scale is outlined. It is applied to five areas of ecological interest in the UK to provide distributed mean monthly soil moisture on a 50 m grid. As the model's driving variables—daily rainfall and potential evapotranspiration—are assumed constant over each of the tracts of land, the variability in soil moisture is due to different soil types and to topographic effects. Box plots of the mean monthly simulated soil moisture clearly show the spread of values occasioned by modelling the lateral water movement down the hillslope. The general magnitude of the results are compared with published data wherever possible and there is some discussion of the form of the curve used in the model to describe the attenuation of evapotranspiration with decreasing soil moisture. Copyright © 2000 John Wiley & Sons, Ltd.     

Crustal movement and deformation in Taiwan and its coastal area

Introduction Both Taiwan Island and Chinese mainland belong to Eurasian plate in geological structure. And the nearest distance between Taiwan Island and Fujian Province, which is located on the opposite coast, is only 130 km. Although there are high-precision GPS networks in both Taiwan and Fujian Province, joint GPS measurement cannot be made directly because of the inconvenient contact due to the strait between them. However, the GPS networks arranged on b…     

Variation in soil saturated hydraulic conductivity along the hillslope of collapsing granite gullies

Saturated hydraulic conductivity (K_s) affects the soil hydrological process and is influenced by many factors that exhibit strong spatial variations. To accurately measure K_s and its scale, spatial variability and relationship with collapsing gullies, we analysed four double-ring infiltrometer diameters in three soil layers during in situ experiments designed to measure K_s in two typical collapsing gullies (three slope sites) in Tongcheng County of China. The results showed that K_s increased with increasing inner ring diameter, but no significant difference existed between inner diameters of 30 and 40 cm. The K_s in red soil layers was higher than that in sandy soil layers, the transition layers had the lowest values. K_s also varied with slope position, gradually decreasing with distance from the gully head. The suggestion is that the spatial variation in K_s is affected not only by the intrinsic soil properties but also by the interaction with the collapsing gully.     

Macroscale surface roughness and frictional resistance in overland flow

The hydraulics of overland flow on rough granular surfaces can be modelled and evaluated using the inundation ratio rather than the flow Reynolds number, as the primary dimensionless group determining the flow behaviour. The inundation ratio describes the average degree of submergence of the surface roughness and is used to distinguish three flow regimes representing partially inundated, marginally inundated and well-inundated surfaces. A heuristic physical model for the flow hydraulics in each regime demonstrates that the three states of flow are characterized by very different functional dependencies of frictional resistance on the scaled depth of flow. At partial inundation, flow resistance is associated with the drag force derived from individual roughness and therefore increases with depth and percentage cover. At marginal inundation, the size of the roughness elements relative to the depth of flow controls the degree of vertical mixing in the flow so that frictional resistance tends to decrease very rapidly with increasing depth of flow. Well-inundated flows are described using rough turbulent flow hydraulics previously developed for open channel flows. These flows exhibit a much more gradual decrease in frictional resistance with increasing depth than that observed during marginal inundation. A data set compiled from previously published studies of overland flow hydraulics is used to assess the functional dependence of frictional resistance on inundation ratio over a wide range of flow conditions. The data confirm the non-monotonic dependence predicted by the model and support the differentiation of three flow regimes based on the inundation ratio. Although the percentage cover and the surface slope may be of importance in addition to the inundation ratio in the partially and marginally inundated regimes, the Reynolds number appears to be of significance only in describing well-inundated flows at low to moderate Reynolds numbers. As these latter conditions are quite rare in natural environments, the inundation ratio rather than the Reynolds number should be used as the primary dimensionless group when evaluating the hydraulics of overland flow on rough surfaces. © 1997 by John Wiley & Sons, Ltd.