印度河扇水道堤岸外侧更新世沉积物波发育特征与形成过程分析*

印度河扇更新世发育的沉积物波结构复杂、形态多样,其形成过程的认识程度低。本次研究通过高分辨率地震数据和地震解释技术,研究了印度河扇沉积物波的波长、形态、波峰变化等形态特征;阐述了沉积物波与沉积物变形特征的差异、识别了两者的区分标志;总结了水道堤岸斜坡和区域斜坡上沉积物波的分布规律;在此基础上,讨论了沉积物波的形成机理和控制因素,分析了沉积物波的形成过程,并建立了印度河扇沉积物波的形成模式。研究表明: (1)研究区沉积物波波长平均为486.84 m,最大1473 m;波高在10~60 m之间,平均30 m。(2)沉积物波的形态有对称型和非对称型,其迁移方式有上坡迁移型、加积型和下坡迁移型;沉积物波主要发育在水道堤岸的斜坡上,在区域斜坡上也发育少量的沉积物波,这2种沉积物波波脊的走向差异很大,水道堤岸斜坡上的沉积物波主要分布于水道凹岸堤岸的外侧,距离水道越远其规模(波长、波高)越小,波脊走向近于NE-SW方向,与水道的走向平行或斜交;区域斜坡上的沉积物波波脊的走向多为NW-SE向,平行于区域斜坡的走向,离源区越远规模越大。(3)水道堤岸斜坡上的沉积物波是由水道型浊流在离心力的作用下,溢出水道的凹岸,在堤岸外侧的斜坡上沉积形成的,堤岸斜坡的角度对沉积物波的发育规模影响不大,浊流的强度和输沙量对其规模影响大;区域斜坡上发育的沉积物波是由顺坡而下的非水道化的浊流沉积形成;滑塌变形造成的起伏地貌以及早期沉积物波的存在,也都影响了后期沉积物波的发育。     

Measured performance of the application of EGNOS in the road traffic sector

European Geostationary Navigation Overlay Service (EGNOS) is a satellite-based system developed to improve the performance of GPS in the European region. It not only enhances the estimated positioning accuracy but also provides an integrity solution. We assess the EGNOS performance through analysis of real measurements, performed in different road user environments. We investigate the use of the integrity concept in future Global Navigation Satellite System (GNSS)-based applications in the road environment, considering both suburban and dense urban areas. The analysis is motivated by the fact that there is an increasing number of road applications, such as billing system, transportation of dangerous goods, remote tracking of trucks and snow plows, fleet management and “pay as you go” car insurances, where the system liability has to be guaranteed. The scope of the analysis is to investigate to which extent the use of the integrity concept can be used for such purpose; the assessment is based on real measurement campaigns in representative environments, providing statistical results in terms of accuracy and integrity, and in a wider sense of the feasibility of the use of EGNOS for augmenting the reliability of GNSS positioning for road applications.     

Forest cover change assessment in conflict-affected areas of northwest Pakistan: the case of swat and shangla districts

This study examines the spatial and temporal forest cover changes in Swat and Shangla districts to understand the deforestation pattern in context of the recent security conflict in these districts. We used multi-resolution satellite images to assess the long term deforestation from 2001 to 2009 and also to identify episodic forest cutting areas appeared during the conflict period of Oct. 2007 - Oct. 2008. There are only 58 ha of deforestation identified during the conflict period while 1268 ha of gross annual deforestation were assessed during last eight years. Most of the deforestation patches persist around the administrative boundaries at sub-district levels (tehsils) which can be attributed to ambiguity in unclear jurisdiction between the forest official. The results highlight that the forest cutting appeared in Swat and Shangla during the conflict period is not as significant when compared with the long term deforestation pattern in the area. On the one side the results of the study are supportive to the picture that emerges from international studies which report high rate of deforestation in the country and on the other side it negates any relation between the security situation and the increasing deforestation in the north western Pakistan. The study concludes that deforestation assessments require verification by independent sources of data, such as satellite imagery to improve our understanding of deforestation processes.     

Analyzing the occurrence of floods and droughts in connection with climate change in Punjab province,Pakistan

Natural Hazards - Frequency and intensity of extreme weather events are immensely changing throughout the world. This study aims to give insight into the changing climatic patterns leading to...     

Assessment of seismic hazard of roller compacted concrete dam site in Gilgit-Baltistan of northern Pakistan

The proposed site of the Diamer Bhasha Dam in northern Pakistan is situated in an active tectonic zone with intensive seismicity, which makes it necessary for seismic hazard analysis(SHA). Deterministic and probabilistic approaches have been used for SHA of the dam site. The Main Mantle Thrust(MMT), Main Karakaram Thrust(MKT), Raikot-Sassi Fault(RKSF) and Kohistan Fault(KF) have been considered as major seismic sources, all of which can create maximum ground shaking with maximum potential earthquake(MPE). Deterministically estimated MPE for magnitudes of 7.8, 7.7, 7.6, and 7.1 can be produced from MMT, MKT, RKSF and KF, respectively. The corresponding peak ground accelerations(PGA) of 0.07, 0.11, 0.13 and 0.05 g can also be generated from these earthquakes, respectively. The deterministic analysis predicts a so-called floating earthquake as a MPE of magnitude = 7.1 as close as 10 km away from the site. The corresponding PGA was computed as 0.38 g for a maximum design earthquake at the project site. However, the probabilistic analysis revealed that the PGA with 50% probability of exceedance in 100 years is 0.18 g. Thus, this PGA value related to the operational basis earthquake(OBE) is suggested for the design of this project with shear wave velocity(V_(s30)) equal to 760 m/s under dense soil and soft rock conditions.     

印度河扇水道堤岸外侧更新世沉积物波发育特征与形成过程分析*

印度河扇更新世发育的沉积物波结构复杂、形态多样,其形成过程的认识程度低。本次研究通过高分辨率地震数据和地震解释技术,研究了印度河扇沉积物波的波长、形态、波峰变化等形态特征;阐述了沉积物波与沉积物变形特征的差异、识别了两者的区分标志;总结了水道堤岸斜坡和区域斜坡上沉积物波的分布规律;在此基础上,讨论了沉积物波的形成机理和控制因素,分析了沉积物波的形成过程,并建立了印度河扇沉积物波的形成模式。研究表明: (1)研究区沉积物波波长平均为486.84 m,最大1473 m;波高在10~60 m之间,平均30 m。(2)沉积物波的形态有对称型和非对称型,其迁移方式有上坡迁移型、加积型和下坡迁移型;沉积物波主要发育在水道堤岸的斜坡上,在区域斜坡上也发育少量的沉积物波,这2种沉积物波波脊的走向差异很大,水道堤岸斜坡上的沉积物波主要分布于水道凹岸堤岸的外侧,距离水道越远其规模(波长、波高)越小,波脊走向近于NE-SW方向,与水道的走向平行或斜交;区域斜坡上的沉积物波波脊的走向多为NW-SE向,平行于区域斜坡的走向,离源区越远规模越大。(3)水道堤岸斜坡上的沉积物波是由水道型浊流在离心力的作用下,溢出水道的凹岸,在堤岸外侧的斜坡上沉积形成的,堤岸斜坡的角度对沉积物波的发育规模影响不大,浊流的强度和输沙量对其规模影响大;区域斜坡上发育的沉积物波是由顺坡而下的非水道化的浊流沉积形成;滑塌变形造成的起伏地貌以及早期沉积物波的存在,也都影响了后期沉积物波的发育。     

Multifractal features of the particle-size distribution of suspended sediment in the Three Gorges Reservoir,China

The Three Gorges Reservoir(TGR)in China is the largest hydroelectric project in the world,but the threat of sediment affecting ecological sustainability of the reservoir is a topic of concern.Sediment particlesize distribution(PSD)is informative in understanding sediment transport dynamics and biochemical functions.It is,therefore,important to quantitatively characterize the distribution of sediment particles.In the current study,fractal theory is applied to determine the PSD of suspended sediment in the TGR.The results show that the volumetric fractal dimension(D_v)exhibits a significant seasonal difference(p<0.05),reflecting sediment source and hydrodynamic sorting control the granularity of suspended sediment in the TGR.More specifically,suspended sediment particles are coarser in the wet season than in the dry season for the Yangtze River,and the opposite is true for the Ruxi River,an important tributary.The generalized dimension spectrum,D(q)-q,and multifractal singularity spectrum,f[α(q)]-α(q),were calculated for each suspended sediment sample.Thereafter,the parameters,D(0),D(1),D(2),α(0),Δα(q),andΔf[α(q)],were determined to characterize the PSD.As a result,the coarser suspended sediment during the wet season is characterised by a more complex PSD pattern,with a wider range of particle sizes,greater heterogeneity,and greater homogeneity of distribution over the measurement interval.However,the multifractal structure of the PSD of suspended sediment is more complex during the dry season than during the wet season,with higher local dispersion and variability.The findings of the current study highlight that multifractal analysis provides important insight for understanding the PSD of suspended sediment in the TGR.