Physical sedimentology experiments with sulfuric acid solutions: Implications for Mars?

Physical sedimentology experiments have shown that sulfuric acid solutions may have formed some surface features seen on Mars. Recent data returned from Mars show the presence of jarosite, sulfate salts, hematite, phyllosilicates, and opaline silica, all of which precipitate from some terrestrial sulfuric acid solutions. There is a plethora of geochemical, mineralogical, and sedimentological data indicative of past sulfuric acid systems on Mars, but there has never been a comprehensive study published regarding sulfuric acid as a physical sedimentological agent. In the laboratory, we ran liquids of various compositions over sediments in order to test how these liquids entrain, transport, and deposit sediments. Pure water and concentrated sulfuric acid solutions produced the same general features, such as channels, gullies, and alluvial fans. However, sulfuric acid solutions yielded some distinct sedimentary features not produced by pure water runs. These features, narrow, deeply incised channels of consistent widths, rounded discrete fans, and air bubble “craters”, are similar to some Martian landscape features. These experimental results indicate that acid solutions should be considered a possible sedimentological agent on Mars.     

A numerical modelling and experimental study of flow width dynamics on alluvial fans

Alluvial fans are dynamic landforms, the evolution of which is controlled by both external environmental forcing (climate, tectonics and base level change) and internal process‐form feedbacks. The latter include changes in flow configuration (between sheetflow and channelized flow states), driven by aggradation and degradation, which may in turn promote changes in sediment transport capacity. Recent numerical modelling indicates that such feedbacks may lead to dramatic and persistent fan entrenchment in the absence of external forcing. However, the parameterization of flow width within such models is untested to date and is subject to considerable uncertainty. This paper presents results from an experimental study of flow width dynamics on an aggrading fan in which spatial and temporal patterns of fan inundation are monitored continuously using analysis of digital vertical photography. Observed flow widths are compared with results from a simple theoretical model developed for non‐equilibrium (aggradational) conditions. Results demonstrate that the theoretical model is capable of capturing the first‐order characteristics of width adjustment over the course of the experiment, and indicate that flow width is a function of fan aggradation rate. This illustrates that models of alluvial flow width derived for equilibrium conditions may have limited utility in non‐equilibrium situations, despite their widespread use to date. Copyright © 2009 John Wiley & Sons, Ltd.     

2009年7月15日新西兰南岛西海岸近海地震破裂过程快速反演

用地震破裂过程快速反演方法,在2009年7月15日新西兰南岛西海岸近海地震发生后,采用全球地震台网（GSN）的宽频带地震资料,快速反演了这次地震的破裂过程,并于震后4小时内得出了这次地震破裂过程的反演结果．结果表明,这次新西兰南岛西海岸近海地震的破裂过程具有如下基本特征:① 矩震级约为MW7.8;② 地震主要破裂持续时间约为40s;③ 滑动量在断层面上的分布比较简单,整个地震破裂只包含一个滑动量较大的区域;④ 这次地震基本上是一次单侧破裂事件,破裂主要朝向西南方向．      

Progress in studies on the structure and physical properties of the mantle in China

The studies on the structure and physical properties of the mantle by Chinese geophysicists from 2003 to 2007 are reviewed in this report. It mainly contains studies on the seismic velocity structure of the mantle,anisotropy of the mantle,mantle discontinuities,mantle convection and the physical properties of mantle. The review concerns mainly the contents,the methods used and the results of the studies. It can be found that new progress in the study on the structure and physical properties of mantle has been made in the last four years in China. In some preexis-tent areas much progress has been made,advanced methods have been adopted,extensive international co-operation has been conducted in many ways,and the scope of the co-operation has gradually expanded. More-over,some new fields appear as well.     

国外新构造研究进展述评

过去10多年间,新构造学的研究前沿集中在地表过程和地壳过程相互作用的理论模型和实际观察方面。文中从造山带构造、地表侵蚀过程和气候的相互作用,大陆裂谷带中裂谷段的相互作用,横向水系和夷平面等4个方面介绍了国外的最新研究进展并给予评述。作者认为:在地球动力学模型中包括了地表过程是认识造山带和裂开边缘发育的明显进步;横向水系和夷平面成因的地貌学经典概念依然具有生命力     

Source process of very-long-period events accompanying long-period signals at Cotopaxi Volcano,Ecuador

Renewed seismic activity of Cotopaxi, Ecuador, began in January 2001 with the increased number of long-period (LP) events, followed by a swarm of volcano-tectonic (VT) earthquakes in November 2001. In late June 2002, the activity of very-long-period (VLP) (2 s) events accompanying LP (0.5–1 s) signals began beneath the volcano. The VLP waveform was characterized by an impulsive signature, which was accompanied by the LP signal showing non-harmonic oscillations. We observed temporal changes of both the VLP and LP signals from the beginning until September 2003: The VLP signal gradually disappeared and the LP signal characterized by decaying harmonic oscillations became dominant. Assuming possible source geometries, we applied a waveform inversion method to the observed waveforms of the largest VLP event. Our inversion and particle motion analyses point to volumetric changes of a sub-vertical crack as the VLP source, which is located at a depth of 2–3 km beneath the northeastern flank. The spectral analysis of the decaying harmonic oscillations of LP events shows frequencies between 2.0 and 3.5 Hz, with quality factors significantly above 100. The increased VT activity and deformation data suggest an intrusion of magma beneath the volcano. A release of gases with small magma particles may have repetitively occurred due to the pressurization, which was caused by sustained bubble growth at the magma ceiling. The released particle-laden gases opened a crack above the magma system and triggered the resonance of the crack. We interpret the VLP and LP events as the gas-release process and the resonance of the crack, respectively.     

A stochastic ground motion model with separable temporal and spectral nonstationarities

A fully nonstationary stochastic model for strong earthquake ground motion is developed. The model employs filtering of a discretized white‐noise process. Nonstationarity is achieved by modulating the intensity and varying the filter properties in time. The formulation has the important advantage of separating the temporal and spectral nonstationary characteristics of the process, thereby allowing flexibility and ease in modeling and parameter estimation. The model is fitted to target ground motions by matching a set of statistical characteristics, including the mean‐square intensity, the cumulative mean number of zero‐level up‐crossings and a measure of the bandwidth, all expressed as functions of time. Post‐processing by a second filter assures zero residual velocity and displacement, and improves the match to response spectral ordinates for long periods. Copyright © 2008 John Wiley & Sons, Ltd.     

The behavior of specific sediment yield in different grain size fractions in the tributaries of the middle Yellow River as influenced by eolian and fluvial processes

Based on data from 35 stations on the tributaries of the Yellow River, annual specific sediment yield (Y_s) in eight grain size fractions has been related to basin‐averaged annual sand–dust storm days (D_ss) and annual precipitation (P_m) to reveal the influence of eolian and fluvial processes on specific sediment yield in different grain size fractions. The results show that Y_s in fine grain size fractions has the highest values in the areas dominated by the coupled wind–water process. From these areas to those dominated by the eolian process or to those dominated by the fluvial process, Y_s tends to decrease. For relatively coarse grain size fractions, Y_s has monotonic variation, i.e. with the increase in D_ss or the decrease in P_m, Y_s increases. This indicates that the sediment producing behavior for fine sediments is different from that for relatively coarse sediments. The results all show that Y_s for relatively coarse sediments depends on the eolian process more than on the fluvial process, and the coarser the sediment fractions the stronger the dependence of the Y_s on the eolian process. The Y_s–D_ss and Y_s–P_m curves for fine grain size fractions show some peaks and the fitted straight lines for Y_s–D_ss and Y_s–P_m relationships for relatively coarse grain size fractions show some breaks. Almost all these break points may be regarded as thresholds. These thresholds are all located in the areas dominated by the coupled wind–water process, indicating that these areas are sensitive for erosion and sediment production, to which more attention should be given for the purpose of erosion and sediment control. A number of regression equations were established, based which the effect of rainfall, sand–dust storms and surface material grain size on specific sediment yield can be assessed. Copyright © 2007 John Wiley & Sons, Ltd.     

Modeling fluvial response to in‐stream woody vegetation: implications for stream corridor restoration

River restoration and bank stabilization programs often use vegetation for improving stream corridor habitat, aesthetic and function. Yet no study has examined the use of managed vegetation plantings to transform a straight, degraded stream corridor into an ecologically functional meandering channel. Experimental data collected using a distorted Froude‐scaled flume analysis show that channel expansion and widening, thalweg meandering and riffle and pool development are possible using discrete plantings of rigid, emergent vegetation, and the magnitudes of these adjustments depend on the shape of the vegetation zone and the density of the vegetation. These experimental results were verified and validated using a recently developed numerical model, and model output was then used to discuss mechanistically how rivers respond to the introduction of in‐stream woody vegetation. Finally, a hybrid method of meander design is proposed herein where managed vegetation plantings are used to trigger or force the desired morphologic response, transforming a straight, degraded reach into a more functional meandering corridor. It is envisioned that such numerical models could become the primary tool for designing future stream restoration programs involving vegetation and assessing the long‐term stability of such activities. Copyright © 2007 John Wiley & Sons, Ltd.     

2004年苏门答腊大地震激发的T-波

T-波是由海底地震或者海陆边界俯冲带附近地震激发,并在海洋低速层中传播的声波.2004年12月26日,在印度洋东部印尼苏门答腊岛附近发生MW=9.3级大地震,其产生的能量在印度洋中激发了巨大的海啸,造成了严重的人员伤亡和财产损失,受到了世界科学家们极大的关注.本文从台站(PALK)及台站(DGAR)记录到的地震的信号中,提取出了清晰的高频T-波,并在频率域内分析,最终得到了T-波的频谱已及频率随时间变化图像.另外,通过对大地震时间域和频率域内T-波信号的分析,了解到此次大地震断层破裂过程持续的时间大致为500 s,其间伴随有两次明显的能量释放过程.分析数据表明两次能量释放过程的间隔大致为80~100 s.T-波分析将为推断海洋地震以及海陆边界俯冲带附近地震的特征,提供一种独立的研究手段和方法.