两种地震预警定位方法的比较     

李军 《中国地震研究》2014,(4):502-509

In this paper, according to the Fujian Seismic Network earthquake catalog records, the Tnow method and the Four Stations Continuous Location method （hereinafter called FSCL） put forward by Jin Xing are inspected by using P-wave arrival information of the first four stations of each seismic event. Results show that for earthquakes within the network, both methods can obtain similar location results and location deviations are small for the majority of the events. For earthquakes outside the network, the location deviation may be amplified as the epicentral distance increases, owing to the seismic station distribution which spread toward the side of the epicenter and the small opening angle between seismic stations used for locating and epicenter. For the FSCL method, the impacts of the wave velocity on the location results may be significant for earthquakes outside the network. Thus, selecting a velocity model which is similar to the actual structure of the wave velocity will contribute to improving location results of earthquakes. The FSCL method can locate more seismic events than the Tnow method. It concludes that the Tnow method makes use of mistake information from some non-triggering stations in earthquake catalog, and some P-wave arrivals are not included in the earthquake catalog due to discontinuous records or unclear records of the seismic phase, which induces incorrect location.  相似文献   

陆态网络GNSS连续站分区解算方案的对比分析   总被引：1，自引：0，他引：1  

占伟  武艳强  章力博  朱爽  孟宪纲 《地震》2014,34(4):136-142

针对陆态网络GNSS连续站分区设计了三种方案,其中方案1(区域方案)将测站按区域划分为6个子网,每个子网包含55个测站;方案2(大网方案)分为3个测站全国分布的子网,每个子网包含100 个测站;方案3(小网方案)分为8个测站全国分布的子网,每个子网包含55个测站。按照上述三种方案分别处理了陆态网络2010年第110天至2013年第103天的观测数据,从测站时间序列、点位水平速度场、两点间基线长度三个方面对比分析了三种方案解算结果之间的差异。结果表明,不同的方案解算结果存在差异但差异量值较小。综合.上述分析结果和计算耗时等因素,讨论了陆态网络GNSS连续站分区方案的选取。  相似文献   

Analyses of the impact of climate change on water resources components,drought and wheat yield in semiarid regions: Karkheh River Basin in Iran   总被引：2，自引：0，他引：2       下载免费PDF全文

S. Ashraf Vaghefi  S. J. Mousavi  K. C. Abbaspour  R. Srinivasan  H. Yang 《水文研究》2014,28(4):2018-2032

Water resources availability in the semiarid regions of Iran has experienced severe reduction because of increasing water use and lengthening of dry periods. To better manage this resource, we investigated the impact of climate change on water resources and wheat yield in the Karkheh River Basin (KRB) in the semiarid region of Iran. Future climate scenarios for 2020–2040 were generated from the Canadian Global Coupled Model for scenarios A1B, B1 and A2. We constructed a hydrological model of KRB using the Soil and Water Assessment Tool to project water resources availability. Blue and green water components were modeled with uncertainty ranges for both historic and future data. The Sequential Uncertainty Fitting Version 2 was used with parallel processing option to calibrate the model based on river discharge and wheat yield. Furthermore, a newly developed program called critical continuous day calculator was used to determine the frequency and length of critical periods for precipitation, maximum temperature and soil moisture. We found that in the northern part of KRB, freshwater availability will increase from 1716 to 2670 m³/capita/year despite an increase of 28% in the population in 2025 in the B1 scenario. In the southern part, where much of the agricultural lands are located, the freshwater availability will on the average decrease by 44%. The long‐term average irrigated wheat yield, however, will increase in the south by 1.2%–21% in different subbasins; but for rain‐fed wheat, this variation is from ?4% to 38%. The results of critical continuous day calculator showed an increase of up to 25% in both frequency and length of dry periods in south Karkheh, whereas increasing flood events could be expected in the northern and western parts of the region. In general, there is variability in the impact of climate change in the region where some areas will experience net negative whereas other areas will experience a net positive impact. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

不同降雨模式下膨胀岩边坡模型试验研究     

范秋雁  刘金泉  杨典森  袁敬强 《岩土力学》2016,37(12):3401-3409

采用原状膨胀岩进行室内边坡模型试验,研究膨胀岩边坡在连续降雨和湿-干循环模式下的变形和水分入渗特性,揭示两种模式下膨胀岩边坡的变形破坏模式。试验发现,连续降雨模式下初期数次降雨对膨胀岩边坡变形影响最大,有明显的水平方向位移,后期变形很小且趋向稳定。湿-干循环模式下边坡膨胀变形及深部岩体含水率降雨完成后一段时间才达到峰值,随循环次数及降雨量增大,边坡变形速率及变形量都明显增大,岩体裂隙不断发育,水分入渗深度增大,但限于表面一定深度,对深部岩体影响较小。试验结果对工程应用有一定的指导意义：连续降雨模式初期膨胀较大,须加强和完善初期的排水措施,做好边坡的支挡防护措施;湿-干循环模式下,随循环次数增加,做好坡面的防护措施,以起到保湿防渗作用;两种降雨模式均说明纯膨胀性泥岩边坡不发生典型的圆弧滑动等破坏模式,而工程边坡的滑动多发生在软弱夹层上,因此,要做好该类边坡的软弱夹层特性勘察,对于不含软弱夹层的纯泥岩边坡要重点监测其浅层变形特性。  相似文献   

鄂尔多斯盆地东部盒8段致密砂岩储层特征——以子洲气田清涧地区为例     

郭智  冀光  王国亭  彭艳霞 《现代地质》2016,30(4):880-889

清涧地区位于鄂尔多斯盆地东部,是子洲气田稳产的主力接替区块。研究区面积大,钻井数目少,地质认识程度低,尚处于开发评价阶段。以盒8段为研究对象,开展了沉积、储层等精细地质研究工作,并与苏里格致密砂岩气田进行综合对比,落实了有效砂体的厚度、规模、发育频率,总结了有效砂体在空间的分布规律,认识到区内有效砂体分布零星,连续性差,与心滩等优势相带对应关系较好,平面上主要集中在研究区的西砂带,垂向上在盒8上2、盒8下2小层相对发育。结合地质与试气资料,以“连续性有效厚度”为主要依据,将储层分成好、中、差、干层等4种类型,优选了富集区,按照开发级次将研究区划分为3类区,建议在一类区、二类区优选直井开发,不建议部署水平井开发。本研究为气田开发方案编制提供了地质依据,同时也可对类似气田的地质工作起到借鉴作用。  相似文献   

Reconstructing and understanding the impacts of storms and surges,southern North Sea          下载免费PDF全文

Sue M. Brooks  Tom Spencer  Anna McIvor  Iris Möller 《地球表面变化过程与地形》2016,41(6):855-864

Coastal barriers are ubiquitous globally and provide a vital protective role to valuable landforms, habitats and communities located to landward. They are, however, vulnerable to extreme water levels and storm wave impacts. A detailed record of sub‐annual to annual; decadal; and centennial rates of shoreline retreat in frontages characterized by both high (> 3 m) and low (< 1 m) dunes is established for a barrier island on the UK east coast. For four storms (2006–2013) we match still water levels and peak significant wave heights against shoreline change at high levels of spatial densification. The results suggest that, at least in the short‐term, shoreline retreat, of typically 5–8 m, is primarily driven by individual events, separated by varying periods of barrier stasis. Over decadal timescales, significant inter‐decadal changes can be seen in both barrier onshore retreat rates and in barrier extension rates alongshore. Whilst the alongshore variability in barrier migration seen in the short‐term remains at the decadal scale, shoreline change at the centennial stage shows little alongshore variability between a region of barrier retreat (at 1.15 m a^?1) and one of barrier extension. A data‐mining approach, synchronizing all the variables that drive shoreline change (still water level, timing of high spring tides and peak significant wave heights), is an essential requirement for validating models that predict future shoreline responses under changing sea level and storminess. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

不同海潮模型对GNSS站负荷位移计算的影响     

赵大江  郭春喜  程传录  陈敏  史旗 《大地测量与地球动力学》2016,36(7):654-658

基于古登堡平均地球模型和积分格林函数方法,利用中国近海海潮模型Chinasea 2010、Naoregional 1999和全球海潮模型EOT11a,计算中国沿海GNSS连续运行站上的海潮位移负荷影响,并对其均方根RMS及和方根RSS进行综合分析。结果表明,2种近海模型分潮波位移负荷差异水平分量大部分为亚mm级,垂直分量普遍为mm级,最大达5.8 mm;Chinasea 2010模型比Naoregional 1999模型在中国海域覆盖面积大,2种模型在黄海和东海海域差异较大,在渤海和南海海域差异较小;模型差异与测站位置及潮波频率均有关系,应比较观测资料的负荷改正效果,择优采用适宜本区域的模型。  相似文献   

煤层气含量快速测定方法   总被引：4，自引：0，他引：4  

庞湘伟 《煤田地质与勘探》2010,38(1):29-32

煤和煤层气地质勘探需要在取到钻孔煤心后的很短时间内获得气含量测值,而现行的煤层气含量测定方法难以满足此要求。基于自然解吸法原理和方法,以自然解吸法的测定结果为基准,在保证解吸量、气组成及其含量基本不变的前提下,通过连续观测、适当提高解吸温度等途径,合理、有效地加速解吸。以快速测定法与自然解吸法的对比试验结果为依据,建立了煤层气含量快速测定方法。此方法将煤层气含量测定周期缩短为几h~几d,可以满足煤和煤层气勘探的需求。   相似文献   

Migration and internal architecture of marine dunes in the eastern English Channel over 14 and 56 year intervals: the influence of tides and decennial storms     

Y. Ferret  S. Le Bot  B. Tessier  T. Garlan  R. Lafite 《地球表面变化过程与地形》2010,35(12):1480-1493

Submarine dune dynamics are controlled by tidal currents and wind forces. According to the relative influence of these forces and the nature of dune sediment, different bedform behaviors can be observed. The footprint of the different hydrodynamic agents is recorded into the internal architecture of dunes. This paper is concerned with bedforms that compose the thick sediment wedge located in the eastern English Channel, off the Bay of Somme. This sedimentary archive constitutes an interesting feature to achieve a better understanding of seabed sediment dynamics and its timeline building stages. The dynamics of large submarine dunes, which are organized in fields, are studied thanks to bathymetric and seismic data over the periods 1937–1993 and 1993–2007. Dune morphology presents low lee and stoss side slopes (on average 8° and 3°, respectively) and dune migration rate is not very high. Dune movements are in the direction of residual tidal currents, i.e. toward the east, with mean migration rates around 0·8 to 5 ± 0·25 m yr^?1 and up to 6·6 ± 0·7 m yr^?1, respectively, at multi‐decennial and decennial time scales. The dune internal architecture is complex with superimposed eastward prograding units, displaying locally opposite progradation. Second‐order discontinuities (dip of 0·5°–4° perpendicular to dune crests) constitute dune master bedding. By counting the number of second‐order reflectors between 1937–1993 and 1993–2007, the formation periodicity of these bounding surfaces is estimated to range from 4 to 18 years. These time intervals coincide with the long‐term tidal cyclicities and also with the inter‐annual to decennial variability of storm activity in northern Europe. Two theories were made to interpret the dune internal structures: the second‐order surfaces are interpreted either as the depositional surfaces corresponding to the marks of weak energy periods (weak tidal and storm action), or as erosive surfaces due to an opposite direction of dune migration provoked temporarily by exceptional storms from the northeast. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Morphodynamique d'une dune sous-marine du détroit du pas de CalaisMorphodynamics of an undersea sandwave of the Dover Straits     

Déborah Idier  Axel Ehrhold  Thierry Garlan 《Comptes Rendus Geoscience》2002,334(15):1079-1085

This paper investigates the dynamics of sandwaves in relationship with tidal currents and weather conditions. The studied sandwaves are located in the Dover Straits and are covered by megaripples. These megaripples have migration speeds of $\text{1 }\text{m}\text{h}{}^{\mathrm{?1}}$ and slopes of 34°, suggesting the potential for avalanches to occur along the flanks of the sandwave. Tidal cycles without reversing currents were observed during stormy weather. Wind-induced currents lead to a unidirectional migration of megaripples and sandwaves. Well-defined areas without megaripples were observed and correlated with an increase in sandwave height. We propose interpretations for understanding sandwave saturation and migration. To cite this article: D. Idier et al., C. R. Geoscience 334 (2002) 1079–1085.  相似文献