A study of microearthquake seismicity and focal mechanisms within the Sea of Marmara (NW Turkey) using ocean bottom seismometers (OBSs)

We have carried out seismological observations within the Sea of Marmara (NW Turkey) in order to investigate the seismicity induced after Gölcük–İzmit (Kocaeli) earthquake (M_w 7.4) of August 17, 1999, using ocean bottom seismometers (OBSs). High-resolution hypocenters and focal mechanisms of microearthquakes have been investigated during this Marmara Sea OBS project involving deployment of 10 OBSs within the Çınarcık (eastern Marmara Sea) and Central-Tekirdağ (western Marmara Sea) basins during April–July 2000. Little was known about microearthquake activity and their source mechanisms in the Marmara Sea. We have detected numerous microearthquakes within the main basins of the Sea of Marmara along the imaged strands of the North Anatolian Fault (NAF). We obtained more than 350 well-constrained hypocenters and nine composite focal mechanisms during 70 days of observation. Microseismicity mainly occurred along the Main Marmara Fault (MMF) in the Marmara Sea. There are a few events along the Southern Shelf. Seismic activity along the Main Marmara Fault is quite high, and focal depth distribution was shallower than 20 km along the western part of this fault, and shallower than 15 km along its eastern part. From high-resolution relative relocation studies of some of the microearthquake clusters, we suggest that the western Main Marmara Fault is subvertical and the eastern Main Marmara Fault dips to south at 45°. Composite focal mechanisms show a strike-slip regime on the western Main Marmara Fault and complex faulting (strike-slip and normal faulting) on the eastern Main Marmara Fault.     

建筑物群中多上行先导三维模型的建立

为实现对地闪过程中多上行先导现象的模拟,在已有三维随机放电参数化方案基础上,植入多先导始发与发展模块以建立高建筑群多上行先导模型,利用电场并行计算技术提高模拟效率。将新模型应用于实际地闪模拟并就统计数据与先导形态特征同观测数据进行对比。结果表明：上行未连接先导长度为12~709 m,起始高度为360~600 m,距连接点水平距离为255~1026 m,距下行先导最近分支的距离为326~589 m,与观测统计结果具有较高的一致性;形态上再现了实际地闪个例F1215中上行未连接先导始发时间早,通道笔直的特点,也能够模拟下行先导与单上行先导头部、单上行先导侧面、多上行先导中连接先导头部、多上行先导中连接先导侧面4种已有观测记录的连接情况,为后续研究提供基础模型。分析模拟结果初步得出结论：最高的广州塔能够对附近一定范围建筑起保护作用且能吸引较远处的下行先导分支;多先导的始发与最后一跳的连接受地面高建筑物群分布、高度以及下行先导位置综合影响。     

Effect of shallow and narrow water on added mass of cylinders with various cross-sectional shapes

The sway, heave and roll added masses of three uniform cylinders with semi-circular, rectangular and triangular cross-sectional shapes in shallow and narrow water are numerically analysed. The method is based on simulation of the potential flow induced by the cylinder's mode of motion. The effects of shallow and narrow water on added mass are analysed and presented. It is concluded that the shallow and narrow water effects on added mass depend on the different cross-section shapes of the cylinders. In particular, the water depth effect on sway added mass is stronger than that on heave added mass while the narrow water effect on sway is weaker than that on heave. The shallow water effect on added mass tends to weaken the narrow water effect. Lastly the effect of shallow and narrow water on added mass on a rectangular cylinder is the strongest while that on a triangular cylinder is the weakest.     

Characteristics of mineral element content of alpine vegetation in permafrost region on Qinghai-Tibetan Plateau

The content characteristics of 16 elements (Al, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, and Zn) in 23 plant species collected from the Qinghai-Tibetan Plateau permafrost region were investigated using ICP-OES. Results show that the average contents of Ca, K, Mg, Fe and P were higher than 1,000 mg/kg, those of Al, Na, Zn and Cr ranged between 10–1,000 mg/kg and those of Cu, Li, Pb and Mo were less than 10 mg/kg. The levels of Al, Ca, K, Mg and Na were within the scope of the reported terrestrial plant element content, those of Sr, Fe and Cr were higher than the average of the terrestrial plants and the maximum content of Mn was higher than the upper limit of the reported Mn content. The main character of the element content was of the Ca>K type, however, in terms of Cyperaceae species the element content character was K>Ca type. The contents of Ca, Li, Mg and Sr in Gramineae and Cyperaceae species were higher than those in other species and the contents of Ca, K, Mg, Fe, P, Al and Na in all collected plants were higher than those of other elements. Zn had weak variability with the lowest coefficient (i.e., 7.81%), while other elements had strong variability. The ratio of maximum content to minimum content indicated Ca and K had less change than other elements in the Qinghai-Tibetan Plateau permafrost region. Element content of alpine vegetation in the Qinghai-Tibetan Plateau permafrost region mainly shows a positive correlation, among which the correlation coefficient between Al and Pb, Al and Fe, Mo and Cr, Pb and Fe, Sr and Li were higher than 0.9, and negative correlation had no statistical significance. The correlation between Al and Fe, Mg, Mn in the Qinghai-Tibetan Plateau permafrost region were consistent with that reported in Kunlun Mountains.     

Investigations and assessment of the landslide hazards of Fengdu county in the reservoir region of the Three Gorges project on the Yangtze River

The spatial database of landslides in Fengdu County of the reservoir region of the Three Gorges project (TGP) on the Yangtze River was compiled from a variety of different sources including field investigations on landslides, existing catalogues and archives on landslides, reports of meteorological events and human engineering activities that triggered slope failures. The major factors that are found to have affected the slope stabilities are outlined, and an assessment and zonation of landslide hazards of the region is made using an integrated information model, which is divided into destructive, disastrous, likely disastrous and essentially non-disastrous areas from the assessment of landslide hazards. The destructive and disastrous areas are respectively 1.9 and 13.8% of the total region, mostly being nearby townships, highways along the south bank of the Yangtze River and residential quarters along two flanks of the Yangtze River and its distributaries, that will impose direct impact to highway transportation and residential lives, and may effect to some degree the navigation of the Yangtze River, reservoir banks, and building of cities and towns.     

Ekman动量近似下中间边界层模式中的风场结构

发展了一个准三维的、中等复杂的边界层动力学模式，该模式包含了EKman动量近似下的惯性加速度和Blackadar的非线性湍流粘性系数，它进一步改进了Tan和Wu(1993）提出的边界层理论模型。该模型在数值计算复杂性上与经典Ekman模式相类似，但由于包含了Ekman动量近似下的惯性项，使得该模式比传统Ekman模式更近于实际过程。中详细地比较了该模式与其他简化边界层模式在动力学上的差异，结果表明：在经典的Ekman模式中，由于忽略了流动的惯性项作用，导致在气旋性切变气流（反气旋性切变气流）中风速和边界层顶部的垂直速度的高估（低估），而在半地转边界层模式中，由于高估了流动惯性项的作用，结果与经典Ekman模式相反。同样，该模式可以应用于斜压边界层，对于Ekman动量下的斜压边界层风场同时具有经典斜压边界层和Ekman动量近似边界层的特征。     

Numerical simulation of longitudinal settlement of shield tunnel in the coastal city Shanghai

Until now more than 14 subway lines are in operation and some new lines are being built in the coastal city Shanghai. The longitudinal settlement of shield tunnel has significant effect on the safety of the subway operation. In this paper, the deformation of the shield tunnel and the surrounding soil were analyzed by the establishment of a three-dimensional model. The vertical displacements of four paths (Path 1 is on the ground; Path 2 is at the top of the tunnel; Path 3 is in the middle of the tunnel; Path 4 is at the bottom of the tunnel) are affected by the nature of the soil. The horizontal displacement is smaller than the vertical displacement and horizontal displacement of the clay is larger than that of the sand. The distribution of the pore pressure changes with soil properties around the tunnel. The pore pressure of the sand layer is larger than that of the clay layer at the same depth of underlying soil.     

石笋氧同位素和微量元素记录的陕南地区4200～2000a B.P.高分辨率季风降雨变化

基于陕南祥龙洞石笋XL2的19个230Th年龄、218个氧同位素分析以及896个Sr/Ca分析数据,高分辨率重建了4200～1972a B.P.期间陕南地区季风降雨变化.重建结果显示陕南地区这一时期季风降雨有显著的127～105a和57a周期,可能分别受控于太阳活动、PDO和/或AMO的变化.重建时段有3次百年尺度的干旱事件,分别发生于2200～2100a B.P.,2900～2700a B.P.和3600～3400a B.P.,其中2900～2700a B.P.干旱事件对应于北大西洋地区2.8ka冷事件.对比研究显示,尽管祥龙洞石笋和董哥洞石笋δ18O记录整体一致,但除了2900～ 2700aB.P.干旱事件之外,其他两次干旱事件在董哥洞石笋记录中并不明显.而尽管总体上祥龙洞和和尚洞石笋δ18O记录的差异要大,但XL2的3次干旱事件在和尚洞记录都有明显体现.有精确年代控制的祥龙洞、董哥洞及和尚洞石笋氧同位素记录的差异,揭示晚全新世我国季风降雨在十一百年尺度存在区域差异.     

东南亚夏季风中断、过渡与活跃期的区域能量学研究

对两次季风演变过程的能量学研究表明，季风演变具有鲜明的阶段性能量学特征。中断期，积云加热小，两个转换函数值很小；过渡期，积云加热增强明显，两个转换函数值迅速加大，边界输送作用也明显朝有利方向变化，同时，纬向平均气流变为向季风供应扰动动能；活跃期，大尺度加热变得重要，积云加热维持，两个转换函数也保持大的正值。分析表明，印度季风东传对东南亚季风活跃的触发作用是重要的，但季风活跃的维持则主要依靠区域内部能量学过程。     

A comparative study of landslide susceptibility mapping using weight of evidence,logistic regression and support vector machine and evaluated by SBAS-InSAR monitoring: Zhouqu to Wudu segment in Bailong River Basin,China

The determining of landslide-prone areas in mountainous terrain is essential for land planning and hazard mitigation. In this paper, a comparative study using three statistical models including weight of evidence model (WoE), logistic regression model (LR) and support vector machine method (SVM) was undertaken in the Zhouqu to Wudu segment in the Bailong River Basin, Southern Gansu, China. Six conditionally independent environmental factors, elevation, slope, aspect, distance from fault, lithology and settlement density, were selected as the explanatory variables that may contribute to landslide occurrence based on principal component analysis (PCA) and Chi-square test. The relation between landslide distributions and these variables was analyzed using the three models and the results then used to calculate the landslide susceptibility (LS). The performance of the models was then evaluated using both the highly accurate deformation signals produced by using the Small Baseline Subset Interferometric Synthetic Aperture Radar technique and Receiver Operating Characteristic (ROC) curve. Results show more deformation points in areas with high and very high LS levels, and also more stable points in areas with low and very low LS levels for the SVM model. In addition, the SVM has larger area under the ROC curve. It indicates that the SVM has better prediction accuracy and classified ability. For the interpretability, the WoE derives the class of factors that most contributed to landsliding in the study area, and the LR reveals that factors including elevation, settlement density and distance from fault played major roles in landslide occurrence and distribution, whereas the SVM cannot provide relative weights for the variables. The outperformed SVM could be employed to determine potential landslide zones in the study area. Outcome of this research would provide preliminary basis for general land planning such as choosing new urban areas and infrastructure construction in the future, as well as for landslide hazard mitigation in Bailong River Basin.