Microseismic events enhancement and detection in sensor arrays using autocorrelation‐based filtering          下载免费PDF全文

Entao Liu  Lijun Zhu  Anupama Govinda Raj  James H. McClellan  Abdullatif Al‐Shuhail  SanLinn I. Kaka  Naveed Iqbal 《Geophysical Prospecting》2017,65(6):1496-1509

Passive microseismic data are commonly buried in noise, which presents a significant challenge for signal detection and recovery. For recordings from a surface sensor array where each trace contains a time‐delayed arrival from the event, we propose an autocorrelation‐based stacking method that designs a denoising filter from all the traces, as well as a multi‐channel detection scheme. This approach circumvents the issue of time aligning the traces prior to stacking because every trace's autocorrelation is centred at zero in the lag domain. The effect of white noise is concentrated near zero lag; thus, the filter design requires a predictable adjustment of the zero‐lag value. Truncation of the autocorrelation is employed to smooth the impulse response of the denoising filter. In order to extend the applicability of the algorithm, we also propose a noise prewhitening scheme that addresses cases with coloured noise. The simplicity and robustness of this method are validated with synthetic and real seismic traces.  相似文献   

Spatial behaviour of Rayleigh waves in layered half‐spaces under active surface sources          下载免费PDF全文

Hua‐You Chai  Tian‐Bin Li  Kok‐Kwang Phoon  Elton J. Chen  Dian‐Ji Zhang 《Geophysical Prospecting》2017,65(4):992-1003

In the free state, Rayleigh waves are assumed to travel in the form of planar wavefronts. Under such an assumption, the propagation behaviour of the modes of Rayleigh waves in layered half‐spaces is only frequency dependent. The frequency behaviour, which is often termed as dispersion, is determined by the shear wave velocity profile of layered soils within the depth related to wavelength (or frequency). According to this characteristic, the shear wave velocity profile can be back‐analysed from the dispersion. The technique is widely used in the surface wave testing. However, the wavefronts of Rayleigh waves activated by the surface sources are non‐planar. The geometric discrepancy could result in Rayleigh waves manifesting distance‐dependent behaviour, which is referred to as spatial behaviour in this paper. Conventional analysis ignoring this spatial behaviour could introduce unexpected errors. In order to take the effects of sources on the propagation behaviour into account, a new mathematical model is established for Rayleigh waves in layered elastic media under vertical disc‐like surface sources using the thin‐layer method. The spatial behaviour of the activated modes and the apparent phase velocity, which is the propagation velocity of Rayleigh waves superposed by the multiple modes, are then analysed. Aspects of the spatial behaviour investigated in this paper include the equilibrium path, the particle orbit, and the geometric attenuation of the activated Rayleigh waves. The results presented in this paper can provide some guidelines for developing new inverse mathematical models and algorithms.  相似文献   

Reply to Joel Sarout's comment on “Physical constraints on c13 and δ for transversely isotropic hydrocarbon source rocks”          下载免费PDF全文

Fuyong Yan  De‐hua Han  Qiuliang Yao 《Geophysical Prospecting》2017,65(1):381-381

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Evaluation of Hydraulic Properties of Aquitards Using Earthquake‐Triggered Groundwater Variation          下载免费PDF全文

Shih‐Jung Wang  Kuo‐Chin Hsu  Chein‐Lee Wang  Wen‐Chi Lai  Liang‐Tzu Hsu 《Ground water》2017,55(5):747-756

The hydraulic properties of aquitards are not easily obtained because monitoring wells are usually installed in aquifers for groundwater resources management. Earthquake‐induced crust stress (strain) triggers groundwater level variations over a short period of time in a large area. These groundwater anomalies can be used to investigate aquifer systems. This study uses a poroelastic model to fit the postseismic variations of groundwater level triggered by the Chi‐Chi earthquake to evaluate the hydraulic properties of aquitards in the Jhoushuei River alluvial fan (JRAF), Taiwan. Six of the adopted eight wells with depths of 70 to 130 m showed good agreement with the recovery theory. The mean hydraulic conductivities (K) of the aquifers for the eight wells are 1.62 × 10^?4 to 9.06 × 10^?4 m/s, and the thicknesses are 18.8 to 46.1 m. The thicknesses of the aquitards are 11.3 to 42.0 m. Under the isotropic assumption for K, the estimated values of K for the aquitards are 3.0 × 10^?8 to 2.1 × 10^?6 m/s, corresponding to a silty medium. The results match the values obtained for the geological material of the drilling core and those reported in previous studies. The estimated values were combined with those given in previous studies to determine the distribution of K in the first two aquitards in the JRAF. The distribution patterns of the aquitards reflect the sedimentary environments and fit the geological material. The proposed technique can be used to evaluate the K value of aquitards using inverse methods. The inversion results can be used in hydrogeological analyses, contaminant modeling, and subsidence evaluation.  相似文献   

Impacts of Seasonal Pumping on Stream‐Aquifer Interactions in Miryang,Korea          下载免费PDF全文

Hyeonju Lee  Min‐Ho Koo  Yongcheol Kim 《Ground water》2017,55(6):906-916

Large agricultural fields in South Korea are located mostly on alluvial plains, where a significant amount of groundwater is used for heating of water‐curtain insulated greenhouses. Such greenhouses are commonly used for crop cultivation during the winter dry season from November to March. After use the groundwater is discharged directly into streams, causing groundwater depletion. A hydrogeological study was carried out in a typical agricultural area of this type, located on an alluvial aquifer near the Nakdong River. Groundwater levels, chemical characteristics, and temperatures from 68 observation wells were analyzed to determine the impacts of seasonal groundwater pumping on the groundwater system and stream‐aquifer interactions. Our results show that the groundwater system has not yet reached a state of dynamic equilibrium. Decades of excessive seasonal pumping have caused a gradual decline of groundwater levels, leading to groundwater depletion, especially in areas further from the river. Seasonal pumping has also significantly affected groundwater quality in the aquifer near the river. Groundwater temperature is decreasing (in this case a disadvantage), and saline groundwater is being diluted by induced recharge. The results of this study provide a basic outline for effective integrated water management that is widely applicable in South Korea.  相似文献   

Impacts of domestic sewage effluent on phytoplankton from Bedford Basin, eastern Canada   总被引：2，自引：0，他引：2  

Youlian Pan  D.V. Subba Rao 《Marine pollution bulletin》1997,34(12):1001-1005

The impact of domestic sewage effluent (SE) on the dynamics of phytoplankton assemblages from Bedford Basin was evaluated in the laboratory. Phytoplankton production and chlorophyll a increased proportionally with SE enrichment. Phytoplankton species composition also changed. The potentially harmful diatoms, Pseudonitzschia spp., present initially in small numbers (600 cells 1⁻¹) in Bedford Basin seawater, and became dominant (3–5×10⁶ cells 1⁻¹) when the seawater was enriched with 0.5–5% untreated SE. With higher proportions of SE, other harmful species such as Fragilaria spp. and Euglena spp. became dominant (7−15×10⁶ and 2.2×10⁴ cells 1⁻¹, respectively). Treatment of SE with UV light or activated charcoal seems to favour growth of benign species, such as Chaetoceros socialis, Skeletonema costatum and Thalassiosira spp., but not harmful species such as Pseudonitzschia spp. Further research on UV treatment of domestic sewage is recommended.  相似文献   

Cyclic behavior and failure mechanism of self‐centering energy dissipation braces with pre‐pressed combination disc springs          下载免费PDF全文

Long‐He Xu  Xiao‐Wei Fan  Zhong‐Xian Li 《地震工程与结构动力学》2017,46(7):1065-1080

A new type of bracing system composed of friction energy dissipation devices for energy dissipation, pre‐pressed combination disc springs for self‐centering and tube members as guiding elements is developed and experimentally studied in this paper. The mechanics of this system are explained, the equations governing its hysteretic responses are outlined and large‐scale validation tests of two braces with different types of disc springs are conducted under the condition of low cyclic reversed loading. The experimental results demonstrate that the proposed bracing system exhibits a stable and repeatable flag‐shaped hysteretic response with an excellent self‐centering capability and effective energy dissipation throughout the loading protocol. Furthermore, the maximum bearing force and stiffness are predicted well by the equations governing its mechanical behavior. Fatigue and destructive test results demonstrate that the proposed bracing system can maintain stable energy dissipation and self‐centering capabilities under large deformation cyclic loading even when the tube members exceed the elastic limit and that a larger bearing capacity is achieved by the system that has disc springs without a bearing surface. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Spatial coherency analysis of seismic ground motions from a rock site dense array implemented during the Kefalonia 2014 aftershock sequence          下载免费PDF全文

A. Svay  V. Perron  A. Imtiaz  I. Zentner  R. Cottereau  D. Clouteau  P.‐Y. Bard  F. Hollender  F. Lopez‐Caballero 《地震工程与结构动力学》2017,46(12):1895-1917

The objective of studies presented in this paper is to analyse the spatial incoherency of seismic ground motions using signals from a velocimeter dense array located on a rock site, recording the aftershock sequence of the two M6 Kefalonia earthquakes that occurred in January/February 2014 (Kefalonia island, Greece). The analyses are carried out with both horizontal and vertical components of velocigrams for small separation distances of stations (<100 m). The coherencies of seismic ground motions identified from strong motion windows are compared with those identified from coda parts of signals. It is realized that there is no significant difference between the coherencies estimated from those two parts of signals. The influence of earthquake event number on the result of coherencies and the dispersions of coherencies estimated from different earthquake events are presented. Finally, coherencies estimated from the dense array are compared with several coherency models proposed and widely used in the literature. The possibility of modifying some parameters of those existing coherency models to fit with in situ coherencies are discussed and presented. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

The effect of lithology on valley width,terrace distribution,and bedload provenance in a tectonically stable catchment with flat‐lying stratigraphy          下载免费PDF全文

Amanda Keen‐Zebert  Mark R. Hudson  Stephanie L. Shepherd  Evan A. Thaler 《地球表面变化过程与地形》2017,42(10):1573-1587

How rock resistance or erodibility affects fluvial landforms and processes is an outstanding question in geomorphology that has recently garnered attention owing to the recognition that the erosion rates of bedrock channels largely set the pace of landscape evolution. In this work, we evaluate valley width, terrace distribution, and bedload provenance in terms of reach scale variation in lithology in the study reach and discuss the implications for landscape evolution in a catchment with relatively flat‐lying stratigraphy and very little uplift. A reach of the Buffalo National River in Arkansas was partitioned into lithologic reaches and the mechanical and chemical resistance of the main lithologies making up the catchment was measured. Valley width and the spatial distribution of terraces were compared among the different lithologic reaches. The surface grain size and provenance of coarse (2–90 mm) sediment of both modern gravel bars and older terrace deposits that make up the former bedload were measured and defined. The results demonstrate a strong impact of lithology upon valley width, terrace distribution, and bedload provenance and therefore, upon landscape evolution processes. Channel down‐cutting through different lithologies creates variable patterns of resistance across catchments and continents. Particularly in post‐tectonic and non‐tectonic landscapes, the variation in resistance that arises from the exhumation of different rocks in channel longitudinal profiles can impact local base levels, initiating responses that can be propagated through channel networks. The rate at which that response is transmitted through channels is potentially amplified and/or mitigated by differences between the resistance of channel beds and bedload sediment loads. In the study reach, variation in lithologic resistance influences the prevalence of lateral and vertical processes, thus producing a spatial pattern of terraces that reflects rock type rather than climate, regional base level change, or hydrologic variability. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Distribution characteristics and controlling factors of typical heavy metals in Huanghe River estuary,China     

Lu  Yuxi  Pan  Dawei  Yang  Tingting  Wang  Chenchen 《中国海洋湖沼学报》2023,41(1):150-165

Journal of Oceanology and Limnology - The geochemical characteristics and potential controlling factors of colloidal Zn, Cd, and Pb in Huanghe (Yellow) River estuary (HRE), China were investigated....  相似文献