Fault pattern from seabeam processing: The western part of the Blanco Fracture Zone (NE pacific)

The Blanco Fracture Zone, which connects the Juan de Fuca and Gorda ridges, is structurally complex and contains numerous pull-apart basins and accretion centres. It terminates at its western end in two troughs where the Juan de Fuca Ridge progressively dies out. This unusual structure is studied in detail using bathymetric analysis which allows the fault pattern to be determined. The method developed to extract structural information involves numerical treatment of the gridded bathymetry derived from image processing methods. The detailed mapping of the fault pattern shows that the active zone corresponds to a N100° E strike-slip zone which connects the southern end of the Juan de Fuca Ridge with the northeastern edge of the Blanco Trough, via the northwestern wall of the Parks Plateau. The present day direction of the active zone comes after a previous one trending at N115° E, apparently within the same area. The Parks Plateau results from a jump of the plate boundary from the southern to northern limits of the plateau. Deformation over the past 2 Ma results from a northeastward displacement of the junction between the transform zone and the ridge.     

分形城市研究进展：从几何形态到网络关联

城市是人类文明最主要的聚集地,也是一个开放复杂演化巨系统,认识其空间复杂性成为城市科学研究的热点和前沿。城市研究正呈现“从位置和场所向关联和流,从物质空间向城市网络空间”的转向。人类对城市的认识也从“空间是机器”转向“城市有机生命体”。分形是大自然的语言和地理学第四代语言,是挖掘城市空间自组织规律的有效工具,在揭示城市有机体复杂演化机制方面发挥重要作用。目前分形城市研究以指标构建和实证分析为主,缺乏系统的梳理和回顾;内容上侧重几何分形,复杂城市网络视角下的结构分形研究薄弱。本文简要回顾了近30余年来分形城市研究的发展历程,梳理了分形城市研究脉络：从城市形态的几何分形到城市结构与关联的网络分形,从静态分形特征到动态异速生长,并展望了分形城市未来研究方向。     

Organizational Modes and Environmental Conditions of the Severe Convective Weathers Produced by the Mesoscale Convective Systems in South China

Composite radar reflectivity data during April-September 2011-2015 are used to investigate and classify storms in south China(18-27°N; 105^-120°E). The storms appear most frequently in May. They are either linear; cellular or nonlinear systems, taking up 29.45%, 24.51% and 46.04%, respectively, in terms of morphology. Linear systems are subdivided into six morphologies: trailing stratiform precipitation(TS), bow echoes(BE), leading stratiform precipitation(LS), embedded line(EL), no st...     

Post-eruptive development of the Ukinrek East Maar since its eruption in 1977 A.D. in the periglacial area of south-west Alaska

Maar eruptions form small initially steep‐walled basins that contain important archives for the climatic and palaeoenvironmental history in continental areas. The two Ukinrek Maars in south‐western Alaska erupted between 30 March and 9 April 1977 and are the best‐documented maars that have erupted in historical time. This study presents a preliminary analysis of geomorphology, hydrology, magnetic susceptibility, geochemistry and sedimentology data of a field study in August 2004. These results, photographs and topographic surveys are combined for reconstructing the post‐eruptive evolution of Ukinrek East Maar. Within less than 30 years the initially polygonal shape of the crater with nearly vertical crater walls has developed into an almost elliptic form with slopes of 35° inclination on debris fans between a few escarpments. The water table and the crater floor have risen significantly and the crater diameter:depth ratio increased from 3·4 to 5·7, whereas the average height of the crater rim remained almost constant. The main sub‐aerial resedimentation process is formation of rock falls, rock slumps and scree resulting in debris flows and turbidites within the lake that is ice‐covered throughout about half of the year. Distal lake sediments consist of laminated minerogenic clayey‐sandy silts that document frequent turbidity currents. From the linear sedimentation rate of only ca 5 mm year^?1 in 17 cm long cores it may be concluded that the largest portion of the crater sediments formed within the first few months of the maar history, however, this has to be confirmed by future studies.     

Anatomy of a submarine pyroclastic flow and associated turbidity current: July 2003 dome collapse, Soufrière Hills volcano, Montserrat, West Indies

The 12 to 13 July 2003 andesite lava dome collapse at the Soufrière Hills volcano, Montserrat, provides the first opportunity to document comprehensively both the sub‐aerial and submarine sequence of events for an eruption. Numerous pyroclastic flows entered the ocean during the collapse, depositing approximately 90% of the total material into the submarine environment. During peak collapse conditions, as the main flow penetrated the air–ocean interface, phreatic explosions were observed and a surge cloud decoupled from the main flow body to travel 2 to 3 km over the ocean surface before settling. The bulk of the flow was submerged and rapidly mixed with sea water forming a water‐saturated mass flow. Efficient sorting and physical differentiation occurred within the flow before initial deposition at 500 m water depth. The coarsest components (～60% of the total volume) were deposited proximally from a dense granular flow, while the finer components (～40%) were efficiently elutriated into the overlying part of the flow, which evolved into a far‐reaching turbidity current.     

基于路网可达性的城市空间形态集聚分形研究

为将城市形态分形维数从平面空间拓展到交通网络系统,提出一种基于路网的分形集聚维数测算方法,探讨该维数的集聚—扩散性质。以郑州市中心城区为案例区,分别测算了各类功能用地半径集聚维数和路网集聚维数。结果表明：① 各类用地无论在平面中还是在路网中,密度从中心向外围的变化在特定区间内都是均匀的,符合分形特征。② 两种维数均呈现出商业用地<全部建设用地（不含道路与交通设施用地）<居住用地<工业及仓储用地的规律。③ 对于同类功能用地,相对于半径维数,路网集聚维数标度不变区尺度范围更广,对空间的划分也更为精细。④ 同类用地两种集聚维数的分形测量值存在差异,这体现出路网集聚维数对传统测度结果具有一定的延展—集聚修正作用。     

基于“规模—密度—形态”的大连市城市韧性评估

以建设安全城市为目标,依据地理学和景观生态思想方法,构建基于“规模—密度—形态”的三维城市韧性研究框架,并对2000-2016年大连市各县市区的城市韧性进行评估。其中规模韧性利用生态基础设施工具进行度量,密度韧性利用生态足迹与生态承载力工具进行度量,形态韧性基于源汇景观平均距离指数进行度量。还对各年份三类韧性的组合形式进行综合评判。本文认为,“规模—密度—形态”三位一体的韧性评估方法可有效识别城市的韧性特征,是建立城市规划与城市韧性研究之间有效联系的纽带。研究发现：① 规模安全是城市空间扩张的基本约束条件;② 生态承载力是城市密度的安全阈值;③ “源—汇”景观的空间耦合是优良城市形态的基本特征;④ 是“规模—密度—形态”三个韧性的组合状况而不是某一单项指标决定城市的安全性。基于规模、密度、形态韧性及其组合特征判定,为未来大连的城市发展提出建议：① 严格限制中心城区与金州区开发强度,遏制其蔓延式增长趋势;② 严格控制海岸带开发,维持山体和绿色植被斑块的完整性;③ 促进市域均衡开发,提升城市整体韧性;④ 优化新市区开发战略,形成良好城市形态。     

基于GIS和空间句法的空间形态一致性测度

少有学者测度规划道路系统分析出的空间形态与规划师空间形态规划意图的一致性。为更好地落实规划师的空间形态规划意图,以安厚镇为例,提出"基于GIS和空间句法的空间形态一致性测度"方法。主要思路为:首先,基于规划的城镇道路系统用GIS空间分析技术及集成度、智能度等句法变量分析新一轮城镇空间形态,然后,测度分析出空间形态与空间形态规划意图的一致性。测度结果表明经分析出的城镇空间形态与规划师本意的一致性有待改善,主要表现为城镇发展轴整体智能度较低、可理解性不高,城镇空间拓展主轴较大程度偏离原规划拓展方向,城镇发展次轴对空间结构的引导效用高于主轴。     

Late Quaternary Slip-rates and Slip Partitioning on the Southeastern Xianshuihe Fault System,Eastern Tibetan Plateau

Quantitative analysis of the kinematics of the active faults distributed around the Qinghai-Tibetan Plateau is critical to understand current tectonic processes of the plateau. Chronological analysis, based on the comparison among regional climate and geomorphology, digital photogrammetry, offset landforms, and the tectonics were adopted in this study on the Xianshuihe fault in the eastern Tibetan plateau. Two or more offset-age data were obtained for each segment of the Xianshuihe and the Yunongxi faults. The offset landforms, including river terrace, alluvial fan and glacial moraine, provide constraints for the late Quaternary slip rate of the Xianshuihe fault. The left-lateral strike slip rate of the Xianshuihe fault decreases from 17 mm/a on the northwest segment to 9.3 mm/a on the southeast segment. Regarding the Xianshuihe fault zone and its adjacent blocks as a regional tectonic system, vector analysis was used to quantitatively analyze the longitudinal kinematical transformation and transversal slip partitioning on the fault zone in terms of the kinematical parameters of the main faults within the zone. The results show that there is a distributed vertical uplift at a rate of 6.1 mm/yr caused by shortening across the Gongga Mountains region. Based on these results, we established a model of the slip partitioning for the southeastern segment of the Xianshuihe fault zone.     

Analysis of induced seismicity for stress field determination and pore pressure mapping

The focal mechanisms of some one hundred microseismic events induced by various water injections have been determined. Within the same depth interval, numerous stress measurements have been conducted with the HTPF method. When inverted simultaneously, the HTPF data and the focal plane solutions help determine the complete stress field in a fairly large volume of rock (about 15×10⁶ m³). These results demonstrate that hydraulically conductive fault zones are associated with local stress heterogeneities. Some of these stress heterogeneities correspond to local stress concentrations with principal stress magnitudes much larger than those of the regional stress field. They preclude the determination of the regional stress field from the sole inversion of focal mechanisms. In addition to determining the regional stress field, the integrated inversion of focal mechanisms and HTPF data help identify the fault plane for each for each of the focal mechanisms. These slip motions have been demonstrated to be consistent with Terzaghi's effective stress principle and a Coulomb friction law with a friction coefficient ranging from 0.65 to 0.9. This has been used for mapping the pore pressure in the rock mass. This mapping shows that induced seismicity does not outline zones of high flow rate but only zones of high pore pressure. For one fault zone where no significant flow has been observed, the local pore pressure has been found to be larger than the regional minimum principal stress but no hydraulic fracturing has been detected there.