Spatial scale impact on daily surface water and sediment fluxes in Thukela river,South Africa

The on- and off-site effects of soil erosion in many environments are well known, but there is still limited understanding of the soil loss fluxes in downstream direction due, among other factors, to scarce and poor quality. A four year study to (i) evaluate water and sediment fluxes at different spatio-temporal scales and (ii) interpret the results in terms of processes involved and the controlling factors, was conducted in Thukela basin, South Africa. Five hierarchically nested catchments; namely microcatchment (0.23 km²), subcatchment (1.20 km²), catchment (9.75 km²), sub-basin (253 km²) and basin (29,038 km²), were used in addition to fifteen (1 m²) microplots and ten (10 m²) plots on five locations within the microcatchment. The results showed 19% decrease of unit-area runoff (q) from 3.1 L m⁻² day⁻¹ at microplot to 2.5 L m⁻² day⁻¹ at plot scale followed by steeper (56%) decrease at microcatchment scale. The q decreased in downstream direction to very low level (q ≤ 0.26 L m⁻² day⁻¹). The changes in q were accompanied by initial 1% increase of soil loss (SL) from 18.8 g m⁻² day⁻¹ at microplot to 19.1 g m⁻² day⁻¹ at plot scale. The SL also decreased sharply (by 39 fold) to 0.50 g m⁻² day⁻¹ at microcatchment scale, followed by further decrease in downstream direction. The decrease of q with spatial scale was attributed to infiltration losses, while initial increase of SL signified greater competence of sheet than splash erosion. The decrease of SL beyond the plot scale was attributed to redistribution of the soil on the hillslope and deposition on the stream channel upstream of the microcatchment outlet. Therefore, erosion control strategies focussing on the recovery of vegetation on the slope and stabilisation of gullies are recommended.     

河套地震带中小地震的震源机制测定及应力场特征

运用振幅比和CAP方法测定224次地震的震源机制解,进行归一频度统计和震源机制类型时空分析,以考察河套地震带的应力场在模式转换和应力作用方式两方面的变化形态。河套地震带的压应力方位在北东向存在优势分布,张应力方位在北西向存在优势分布,滑动角主要分布在近水平方向,应力场整体表现出继承性运动特征,表明水平剪切拉张运动总体控制了带内断裂的作用模式而多产出走滑型地震,并贯穿整个研究时段,属稳态应力作用模式。在太平洋板块向西俯冲和青藏块体向北运移的联合作用下,河套地震带两侧的阴山隆起和鄂尔多斯块体作相对旋性扭动,最终驱使带内众多北东-近东西向展布的断裂产生水平旋性剪切,构成相对稳定的应力场演化模式。     

2011年盈江5.8级地震前近场流体异常初探

通过对2011年3月10日盈江5.8级地震近场区水位、气汞等前兆观测资料的分析,发现该地震前震中附近区域的前兆观测异常较为显著,2010年初异常开始出现,7月后异常数量显著增加,盈江5.8级地震前1个月前兆异常出现转折、异常数量开始减少;怒江断裂以西的震中附近地区异常以水位升高和气汞浓度增加为主,显示震区附近地区受到挤压,孔隙压力增加的应力状态;短临阶段异常由外围向震中迁移的特征可作为地点预测的参考依据.最后对近场异常从机理上进行了初步的探讨.     

闽粤赣交界区地震震源位置及速度结构研究

采用震源位置及速度结果的联合反演方法确定闽粤赣交界区(24°~26.5°N,114°~117.8°E)地震的震源位置以及震源区速度结构。结果显示:1闽粤赣交界区地震震源平均深度随震级增大而加深的特征明显,即地震震级越大,震源深度越深,但平均深度不超过15 km;越靠近沿海,地震震源深度有加深的趋势。2通过对河源地区、邵武-河源断裂带中段(寻乌-瑞金)区域、政和-大浦断裂带中段(漳平附近)区域以及闽粤近海区域地震剖面研究,发现地震多发生于高低速异常结合部位。     

2013年河北赞皇小震群活动特征及其指示意义

河北省数字地震台网在2013年5月19日至7月15日记录到河北赞皇县发生震群活动,ML-0.9级以上地震229次。震群附近30km之内之前没有发生过5级以上地震,1966年邢台7.2级地震区呈北北东向分布,在其南部存在北西向分支,抵达赞皇附近,发生过少量ML1~2级小震。与较为平静的地震活动背景相比,赞皇震群尤为突出。通过分析震级—频度关系,震群呈现低b值特征;利用振幅比法反演震群ML2级以上11个基本一致的震源机制解,并进一步反演震源区应力场,结果与华北构造应力场完全吻合。结果显示,震群呈北北东方向分布,震源机制也有相应的节面对应,大多数倾向北西西,表明震群为右旋走向滑动。同时,低b值和震源机制一致属于震兆现象,应注意加强赞皇附近区域的震情跟踪研究。     

福建地震台网对中国台湾中深源地震定位方法探究

利用 JOPENS 系统中交互分析软件 MSDP 提供的定位方法,对中国台湾中深源地震进行定位,分析福建地震台网结果与中国台湾公布的地震参数的吻合性,进而判断合适的定位方法。     

基于BLOC86程序的新疆地区震源深度定位软件

介绍基于BLOC86程序的新疆地区震源深度定位软件的原理、主要功能模块和使用效果.利用该软件定位新疆测震台网地震,计算结果稳定性较好,与震中烈度结果有较好的对应关系,有效弥补了大震应急工作对震源深度参数的需求.     

使用中国地震台网资料快速测定中强地震矩震级

利用中国地震台网数字地震资料,选取国内Ms≥5.3地震波形数据,采用长周期波形拟合方法,快速计算2008年至今86个中强震的标量地震矩MO和矩震级Mw,并将Mw与GCMT的测定结果及中国地震台网中心测定的面波震级Ms进行对比.结果表明：矩震级与GCMT测定一致,与中国地震台网中心测定的面波震级关系为Mw=0.86Ms＋0.63.     

Evolution,accessibility and dynamics of road networks in China from 1600 BC to 1900 AD

Before the emergence of modern modes of transport, the traditional road infrastructure was the major historical means of carrying out nationwide socio-economic exchange. However, the history of transport infrastructure has received little attention from researchers. Given this background, the work reported here examined the long-term development of transport networks in China. The national road network was selected for study and the 3500 years from 1600 BC to 1900 AD was chosen as the study period. Indicators were designed for the maturity level of road networks and an accessibility model was developed for the paths of the shortest distance. The evolution of the road network in China since the Shang Dynasty (1600 BC) was described and its major features were summarized to reveal long-term regularities. The maturity level of the road network and its accessibility was assessed and regions with good and poor networks were identified. The relationship between China’s natural, social, and economic systems and the road network were discussed. Our analysis shows that the road network in China has a number of long-term regularities. The continuously expanding road network follows a path of inland expansion especially towards the border areas. However, its coverage and accessibility are characterized by a core-peripheral configuration, which has close relationships with, not only the natural conditions, but also national defense and warfare. The centralization of national power, national land governance, postal transport, the transport of specialized cargos, and international trade are also related to the development of the road network. This research draws attention to the evolving regularities of transport networks.     

溪洛渡库首区蓄水后震源机制分析

目前世界第三大水库溪洛渡的库首区遍布碳酸盐岩、灰岩,存在溶洞,蓄水后水位升高140m左右,随之发生6 000多次地震,但绝大多数是1级以下微震,最大震级仅仅ML3;集中在库岸两侧10km、深度5km、从大坝向上游沿库盆40km长度的范围内。微小地震对于水库、大坝的安全没有产生影响。使用较为密集的水库数字地震台网资料反演得到蓄水前后700多次地震的震源机制,并进一步反演了全区和分区的应力场,发现:震源机制空间取向复杂、破裂类型多样,应力状态不均匀、不稳定。与他人使用大量天然地震资料反演的区域应力场不一致,表明水库诱发地震没有受到区域应力场的严格控制。分析认为库水涌入溶洞、渗透到裂隙、节理,原来存在的小断层面或者间断面的孔隙压力增加,摩擦强度、岩石破裂强度降低以及库水载荷加大造成弹性变形等共同作用是地震的成因。并且首先主要释放的是已经积累的区域应力、局部应力,然后才表现出以库水载荷产生的附加应力为主。库首区没有较大的活动断层,2014年库水位将再度升高数十m,伴随裂隙的贯通,应力场的调整,回流的库水淹没库盆上游,还会发生中小地震乃至中等强度地震。溪洛渡水库大坝抗震设防水准较高,不会造成安全问题。建议在诱发地震继续活动期间,尽早实施详细的水文地质、地球物理探测,提供精细的科学资料,为确定诱发地震的成因、寻找控制诱发地震的技术条件,以减轻突发事件的影响,为其他类似水库发挥示范作用。