Rheologic evolution of low-grade metasedimentary rocks and granite across a large strike-slip fault zone: A case study of the Kellyland fault zone,Maine, USA

We examine a large strike-slip fault zone that juxtaposes low-grade clastic metasedimentary rocks with coarse-grained granite near the brittle-ductile transition. The load-bearing matrixes in granite-derived ultramylonites and pelite and wacke metasedimentary intervals are texturally similar, and all deformed by diffusion-assisted granular flow. Granite underwent rapid strengthening as the pluton cooled followed by rapid weakening driven by brittle grain-size reduction and mixing that catalyzed ultramylonite formation. The textural and mineralogical similarity of pelitic intervals across the zone indicates they experienced little textural and reaction weakening. Wacke intervals record progressive textural and reaction weakening in an open system. Quartz recrystallized grain sizes in granite-derived ultramylonites record ∼2-times more differential stress than those in metasedimentary rocks in the interior of the zone. The relative weakness of metasedimentary rocks is correlated with fluid influx that likely enhanced diffusion and grain-boundary sliding in pelitic and wacke intervals and catalyzed textural and reaction weakening in wacke intervals. The lack of evidence for fluid and ionic communication with granitic rocks indicates that fluid movement was restricted to foliation-parallel pathways within single rock units. This localized fluid influx is the best explanation for the strength contrasts between texturally similar fault rocks deformed by similar mechanisms.     

Assessing hydrogeologic controls on dynamic groundwater storage using long‐term instrumental records of water table levels

This study analyzes a long‐term regional compilation of water table response to climate variability based on 124 long‐term groundwater wells distributed across New England, USA, screened in a variety of geologic materials. The New England region of the USA is located in a humid‐temperature climate underlain by low‐storage‐fractured metamorphic and crystalline bedrock dissected by north–south trending valleys filled with glacial and post‐glacial valley fill sediments. Uplands are covered by thin glacial till that comprises more than 60% of the total area. Annual and multi‐annual responses of the water table to climate variability are assessed to understand how local hydraulic properties and hydrogeologic setting (located in recharge/discharge region) of the aquifer influence the hydrologic sensitivity of the aquifer system to climate variability. This study documents that upland aquifer systems dominated by thin deposits of surface till comprise ~70% of the active and dynamic storage of the region. Total aquifer storage changes of +5 to ?7 km³ occur over the region during the study interval. The storage response is dominated by thin and low permeability surficial till aquifer that fills and drains on a multi‐annual basis and serves as the main mechanism to deliver water to valley fill aquifers and underlying bedrock aquifers. Whereas the till aquifer system is traditionally neglected as an important storage reservoir, this study highlights the importance of a process‐based understanding of how different landscape hydrogeologic units contribute to the overall hydrologic response of a region.     

Long term high frequency sediment observatory in an alpine catchment: The Arc-Isère rivers,France

We present a dataset on to the Arc-Isère long-term environmental research observatory, which is part of the Rhône Basin Long Term Environmental Research Observatory. This alpine catchment located in the French Alps is characterized by high Suspended Particulate Matter (SPM) in anthropogenized valleys. Suspended Sediment Concentrations (SSC) naturally observed in the river are very high, ranging from a few tens of milligrams per litre at low flow to tens of grams per litre during major natural hydrological events (floods, debris flows) or river dam hydraulic flushes. One research objective related to this site is to better understanding the SSC dynamics along the river using a system of nested catchments (Arvan, Arc, and Isère) in order to assess both temporal and spatial dynamics. The data allow the quantification of fine sediment yields and also the evaluation of possible morphological changes due to fine sediment deposition or resuspension. Additionally, the observatory database support studies on contaminants (either dissolved or particulate contaminants). Our monitoring includes six stations with high frequency (2–30 min) streamflow, SSC measurement using turbidity sensors, and associated automatic sampling. Discharge is measured via water level measurements and a rating curve. The oldest station (Grenoble-campus) started recording discharge and concentration data from April 2006 while others stations were built between 2009 and 2011. Data are available in an online data website called ‘Base de Données des Observatoires en Hydrologie’ (Hydrological observatory database, https://bdoh.irstea.fr/ARC-ISERE/ ) with a DOI reference for the dataset. The hydrological and sediment transport time series are stored, managed and made available to a wide community with unfettered access in order to be used at their full extent. This database is used as a data exchange tool for both scientists and operational end-users and there is an associated online tool to compute integrated fluxes.     

Finite strain elastoplastic solutions for the undrained ground response curve in tunnelling

The instantaneous response of saturated low permeability grounds to tunnel excavation is important for deformations and stability close to the tunnel face. It is characterized by zero volume change in combination with the development of excess pore pressures. In tunnelling through poor quality ground under great depth of cover and high in situ pore pressure, heavily squeezing conditions (characterized by very large convergences) may occur soon after excavation. This paper presents exact finite strain analytical solutions for the undrained ground response around cylindrical and spherical openings that are unloaded from uniform and isotropic initial stress states, on the basis of the Modified Cam Clay (MCC) model and the Mohr–Coulomb (MC) model. The solution for a Drucker–Prager material is also given as it requires only a very small modification to the MC solution. The so‐called ground response curve, that is, the relationship between the support pressure and the cavity wall displacement, is derived in closed form for the MC model. The solution for the MCC problem is semi‐analytical in that it uses the trapezium rule for the computation of a definite integral. The influence of the significant parameters of the problem on the predicted deformation behaviour is shown by means of dimensionless charts. Finally, the practical usefulness of the solutions presented is illustrated by applying them to the breccia zones of the planned Gibraltar Strait tunnel – an extreme case of weak, low permeability ground under high pore pressure. The solutions can serve as a trustworthy benchmark for numerical procedures that incorporate material and geometric nonlinearities. Copyright © 2014 John Wiley & Sons, Ltd.     

Richards Bay Harbour: metal exposure monitoring over the last 34 years

Richards Bay Harbour is South Africa’s premier bulk cargo port. It was constructed in the Mhlathuze estuary in 1976 and over the past 34 years has become South Africa’s most modern and largest cargo handling port. Although no official monitoring programme is in progress various studies by different groups have provided relevant data with respect to changing metal levels in brown mussel tissue (Perna perna) over the last 34 years. Eleven elements were analysed in brown mussels from the main channel in Richards Bay Harbour using ICP-MS. The results indicate that the metal concentrations in the mussel tissue remained relatively constant between 1974 and 2005. The mean metal concentrations increased significantly in 2005 possibly due to the construction of the new coal terminal and associated dredging activities. Mean metal concentrations in the 2008 sampling event were also elevated due to increased run off during an above average rainy season.     

Creek enlargement in a low‐energy degrading saltmarsh in southern England

A low‐energy saltmarsh in the Beaulieu River Estuary, southern England was investigated. A geomorphological survey revealed that the creek bank geometry was characterized by the presence of cantilevers, a result of the protection provided by roots over the upper part of the bank. The saltmarsh deposits, consisting mainly of clay and organic matter, have a high resistance to flow‐induced erosion. Short‐term hydrographic deployments revealed that the tidal currents and waves recorded were insufficient to cause erosion of the bank surface. However, pin measurements over a 2‐year period revealed that the tidal creeks within the saltmarsh did experience bank erosion, particularly below the cantilevers, in spite of this low‐energy setting. Bank face erosion was therefore considered to be related to long‐term processes. The bases of the cantilevers were found to be located at a precise level, in relation to the tides. Water level data over a 2‐year period were examined against erosion measured below the cantilevers. The results suggest that the erosion on the bank faces, particularly below the cantilevers, is associated with the frequency of water level variations and long‐term submergence/emergence cycles, which can decrease the bonds between the particles and enable erosion by low tidal and wind‐wave currents within this low‐energy environment. This mechanism is probably responsible for tidal creek enlargement via erosion of the bank face and subsequent bank failure, a process which acts over a long temporal scale (1–10 years). Copyright © 2010 John Wiley & Sons, Ltd.     

基坑开挖对周边环境影响的试验研究

通过基坑开挖的变形测量实例,观测到基坑开挖时坡后土体的沉降和水平位移具有相关性,可以由实测的土体水平位移推算坡后不同深度土层的沉降量,并分别从土体沉降量和沉降曲线的斜率两种特性来确定基坑开挖在坡后土体中产生形变的范围。在判断影响范围时,单纯以建筑物距基坑距离与基坑深度的比值b/H来确定不够准确,应同时考虑基础埋深和沉降分布曲线的形状。     

Spatial differences in sand wave dynamics between the Amsterdam and the Rotterdam region in the Southern North Sea

The optimization of the bathymetric resurvey policy of the Netherlands Hydrographic Service requires insight into sea floor dynamics in the Southern North Sea. To study the spatial variations in sea floor dynamics, the bathymetric archives of the Netherlands Hydrographic Service are analyzed using deformation analysis, a statistical and innovative approach for bathymetric data. Based on the uncertainty of the data, our implementation of deformation analysis selects the significant spatial and temporal parameters, and provides estimates and their uncertainties for those parameters. We focus on sand wave areas in the regions of Rotterdam and of Amsterdam. In those areas, dredging takes place to guarantee a minimum depth. The results reveal a difference in sand wave migration between the two regions, over the past two decades. The dominant wavelengths of the sand waves vary within the regions, but we find a similar wavelength distribution for the two regions. We compare our results to earlier studies of the same sand wave areas in the Rotterdam region, showing similar migration rates, but different wavelengths. It is concluded, based on sand wave dynamics alone, that the Amsterdam region should be assigned a higher resurvey frequency than the Rotterdam region.     

克孜尔水库跨断层形变变化速率的非均匀性特征分析

对克孜尔水库跨断层垂直形变近40年的资料和水平形变近32年的资料进行了分析。研究发现,①跨断层形变的变化速率具有明显的不均匀性,根据数据序列走势,变化速率的不同可分为6个阶段;②水库施工对跨断层形变有一定的影响,水库蓄水对跨断层形变有显著的影响;③水库蓄水达到正常库容量后的新平衡状态下,跨断层形变速率变化几乎是无干扰背景下变化速率的2倍;④区域应力场的增强对跨断层形变趋势性转折有显著性影响。     

乌鲁木齐形变站水准异常变化特征与地震关系的研究

通过对发生在2003年9月27日俄、中、蒙交界Ms≥7.9级和2007年7月20日特克斯Ms≥5.9级地震前后,乌鲁木齐形变台站垂直形变资料异常特征的分析和研究认为,乌鲁木齐形变台站的前兆观测资料具有较好的映震能力,对乌鲁木齐周边及北天山中西部地区5～6级以上地震有较好的震前反应,前兆信息明显。地震前后形变形态表现为低...