A microearthquake survey at the junction of the East Pacific Rise and the Wilkes (9°S) fracture zone

Summary. An ocean bottom seismograph survey of the junction of the East Pacific Rise and the Wilkes fracture zone detected only three microearthquakes beneath the rise crest during seven days of recording. In contrast, during the same period 41 events were detected on the fracture zone, all at distances greater than 10 km from the junction. These results suggest that near the rise crest the thin crust can support sufficient stress only to generate infrequent small earthquakes and that most faulting may take place by aseismic slip. At 10 km from the rise axis part of the crest has become competent enough to support stress, resulting in earthquakes probably at depths of up to 5 km below the sea-bed. Gear 5-waves on the seismometer records indicate that a magma chamber, if it exists near the junction, is less than 10 km across.     

Overlapping spreading centres: 3-D inversion of the magnetic field at 9°03'N on the East Pacific Rise

Summary. Overlapping spreading centres (OSCs) represent a new type of plate boundary interaction in which en échelon rise segments overlap significantly and are not joined by a transform fault.
A three-dimensional Fourier inversion of the magnetic field was performed on an overlapping spreading centre to remove the effects of topography and ridge orientation. A magnetic high exists at the tip of one of the two ridge segments. Forward modelling suggests that the anomalous magnetic field cannot be attributed to the effects of topography alone. The inversion reveals the existence of a magnetization high at the tip of the eastern spreading centre. Maximum magnetization values are consistent with ones obtained in other high amplitude zones in the Pacific as well as with the measured magnetization of samples dredged in the same areas. We suggest that the magnetization high over the eastern ridge tip of the 9°03'N OSC is associated with highly evolved basalts enriched in iron and titanium. Such enrichment may be caused by enhanced crystal fractionation within an axial magma chamber which is intermittent and occasionally freezes as the eastern spreading axis propagates into older lithosphere.     

1901-2012年中国西北地区东部多时间尺度干旱特征

以干旱的多时间尺度特征出发,利用CRU最新数据,计算了考虑降水和气温双因子影响的标准化降水蒸散指数(SPEI),并与标准化降水指数(SPI)进行对比,分析中国西北地区东部1901-2012年不同时间尺度的干旱特征。本文不仅对百年来CRU资料的可靠性进行检验,而且对SPEI在西北地区东部的适应性进行讨论。结果表明:CRU资料可靠性较好,但由于CRU资料本身的属性,1920年以前资料的可靠性不确定。从干旱事件的发生强度及干旱范围分析,SPEI在西北地区东部具有较好的适用性。SPEI与SPI在不同时间尺度下的波动变化一致,短时间尺度主要表现年内或季节特征,长时间尺度则侧重表现年际、年代际特征。将研究区分为高原东北区和陕南区进行分析,1901-2012年高原东北区有4个干期,陕南区有5个干期。针对温度变化对西北地区东部干旱的影响及与SPI对比表明,高温对干旱的贡献不容忽视。     

Comparison of the Upper Mantle Shear Wave Velocity Structure of the Indian Shield and the Tibetan Plateau and Tectonic Implications

Summary. Travel times and waveforms of long-period SH -waves recorded at distances of 10–30° and some SS waveforms are used to constrain the upper mantle velocities down to a depth of 400km beneath both the Indian Shield and the Tibetan Plateau. the shear velocity in the uppermost mantle beneath both the Indian Shield and the Tibetan Plateau is high and close to 4.7 km s⁻¹. the Indian Shield has a fairly thick high velocity lid, and the mean velocity between 40 and 250 km is between 4.58 and 4.68 km s⁻¹. In contrast, S -wave travel times and waveforms of S -waves, as well as a few for SS , show that the mean velocity between 70 and 250km beneath the central and northern part of the Tibetan Plateau is slower by 4 per cent or more than that beneath the Indian Shield and probably is between 4.4 and 4.5km s⁻¹. No large differences in the structure of the two areas below 250 km are required to explain both the arrival times and the waveforms of SH phases crossing Tibet or the Indian Shield. These results show that the structure of Tibet is not that of a shield and imply that the Indian plate is not underthrusting the whole of the Tibetan Plateau at the present time.     

国外大型事件申办热潮:政治视角的解读

对大型事件影响力共识的缺乏与其申办热情成为悖论,一方面其影响效应尚模糊不清,并引起学界的质疑和争议;另一方面城市的申办和举办热情有增无减,因而隐藏在经济目标之下的非经济动机值得关注。文章从已有文献中厘清国外大型事件的申办动机、申办过程及事件后所表征的政治效应,从政治视角解释当前国外大型事件的申办热潮。主要结论如下:1)超越"事件"本身来看,大型事件作为政府政策工具的角色突显;2)大型事件的时效性使得城市得以完成正常情况下难以在短时间内实施的城市空间改造、城市建设,以及将一些重要的政策尽早提上日程,城市采纳事件战略具有复杂的政治动机;3)大型事件的推动者往往是城市商业和政治精英结成的联盟,一方面他们共同致力于推动举办地的经济发展;另一方面他们也借此谋求政治及商业领域的社会资本;4)大型事件被用来作为合法化工具:是展示国家认同的合法化途径;获得公众支持的合法性;获得上一级政府支持,特别是资金支持的合法性;5)发展中国家,特别是非洲国家的申办更体现出其改善国际不平等关系及成为"非洲门户"的意愿。     

1970-2015年中东地区恐怖袭击事件的时空特征分析

中东作为恐怖活动的多发区域,了解其恐怖袭击的时空特征对恐怖活动治理具有重要意义。基于GTD的恐怖袭击事件空间分布数据,运用GIS空间分析方法对中东地区1970—2015年袭击事件的时空特征进行了探索,研究发现：恐怖组织偏好在边境区域活动,超过50%的袭击事件发生在距边界15km的范围内,约80%的袭击事件位于距边界35km范围内;恐怖袭击重心呈现出一定的空间迁移特征,主要分布于伊拉克、叙利亚、黎巴嫩、巴勒斯坦、约旦和以色列等西亚地区,重心的变化与地区之间的武装冲突、战争等具有空间上的关联性;历年的恐怖袭击形成了涉及伊拉克、伊朗、土耳其、以色列、约旦河西岸和加沙地带、黎巴嫩和阿尔及利亚的三处主要集聚区,同时集聚区伴随时间推移发生变化,各时间段的主、次集聚区分布于12个国家与地区,且恐怖主义活动表现出愈发激烈的趋势;恐怖袭击总体上存在显著的空间相关性,在不同时间段内,“高-高”聚类地区具有一定的空间分异性,但恐怖袭击的空间集聚现象愈加明显。     

简论21世纪初美国中东战略中的美国-伊朗关系

美国对伊朗战略是美国中东战略的重要组成部分。伊朗的政治、经济、社会体制的变化将引起中东政治格局的重大变化。9.11事件以后,美国中东战略的焦点转变为“反恐”:军事上以打击恐怖主义组织和活动、占领中东的战略要地为目标,在中东大力传播美国的“民主、人权”意识,在重建伊拉克、阿富汗、推进中东和平路线图的口号下“改造中东”,经济上控制中东的石油天然气资源,扩张美国在中东的市场,实施“美国-中东自由贸易区”构想,弱化中东和平进程的意义,千方百计使美国的国家利益最大化。美国-伊朗关系,始终围绕着两国国家利益这一核心展开。本文简略地分析了21世纪初期以来美国-伊朗关系的特征及其变化、影响当今美国-伊朗关系的重大障碍,预测了美国的伊朗政策走势,结论是:21世纪初期美国-伊朗关系根本改善的可能性不大。     

一种东台吉乃尔盐湖老卤综合利用新工艺

通过对青海东台吉乃尔盐湖老卤进行综合处理,使该盐湖老卤摆脱了生产碳酸锂单个产品成本较高的困扰,从而可以使其有用元素得到综合利用,并且有机地使用其生产流程加入的辅料,使该老卤得到最大限度的综合利用。     

重庆中坝遗址地层Na-Ca元素含量揭示的制盐业兴衰史

在对中坝和玉溪遗址考古断代和AMS14C 测年基础上, 根据对中坝遗址201 个地层样品ICP 等离子发射光谱的Na、Ca、Mg 元素测定及玉溪遗址47 个地层样品的Na、Ca 元素测 定, 发现中坝制盐遗址地层中存在明显的Na、Ca 元素含量反向相关期有35 处之多, 即: 当Ca 元素为峰值时, Na 元素为谷值, 反之亦然。其中, Ca 元素为峰值、Na 元素为谷值的反向相关期有21 次, 揭示出中坝遗址近5 ka 来制盐业有过近21 个兴盛期。另有14 个Na 元素为 峰值、Ca 元素为谷值的反向相关期, 揭示中坝遗址近5 ka 来制盐业也有过近14 个衰落期。考古发掘得出的“中坝制盐业萌发于新石器时代、夏商发展、西周至汉代为鼎盛期、唐宋时代维持稳定发展、宋以后由于海盐进入川江地区导致中坝制盐业逐渐衰落、但20 世纪70-80 年代仍有生产”的结论证明本文Na、Ca 元素含量反向相关性得出的研究结果是正确的。以上研究结果表明, 中坝制盐遗址中Na、Ca 元素含量有明显的反向相关规律, 这一规律可以用于揭示盐业遗址的制盐业兴衰过程历史。     

Shear and compressional velocity models of the mantle from cluster analysis of long-period waveforms

We present a new technique for the efficient measurement of the traveltimes of long period body wave phases. The technique is based on the fact that all arrivals of a particular seismic phase are remarkably similar in shape for a single event. This allows the application of cross-correlation techniques that are usually used in a regional context to measure precise global differential times. The analysis is enhanced by the inclusion of a clustering algorithm that automatically clusters waveforms by their degree of similarity. This allows the algorithm to discriminate against unusual or distorted waveforms and makes for an extremely efficient measurement technique.
This technique can be applied to any seismic phase that is observed over a reasonably large distance range. Here, we present the results of applying the algorithm to the long-period channels of all data archived at the IRIS DMC from 1976 to 2005 for the seismic phases S and P (from 23° to 100°) and SS and PP (from 50° to 170°). The resulting large data sets are inverted along with existing surface wave and updated differential traveltime measurements for new mantle models of S and P velocity. The resolution of the new model is enhanced, particularly, in the mid-mantle where SS and PP turn. We find that slow anomalies in the central Pacific and Africa extend from the core–mantle boundary to the upper mantle, but their direct connection to surface hotspots is beyond our resolution. Furthermore, we find that fast anomalies that are likely associated with subducting slabs disappear between 1700 and 2500 km, and thus are not continuous features from the upper to lower mantle despite our extensive coverage and high resolution of the mid-mantle.     

Contributions from oceanic and ionospheric dynamos to the lunar daily variation at Alibag

Summary. The contributions from the oceanic and ionospheric dynamos, L_o and L_I respectively, to the geomagnetic lunar daily variation, L , at Alibag, a coastal station in the Indian equatorial region, are calculated from the L harmonics derived from a 41–yr long series of observations. The analysis in the calendar months shows a steady and significant ocean dynamo contribution in the vertical component, Z, in all the months except April. Examination, by an analysis of the data year by year, of the association of L_o and L_I with varying solar and magnetic activities reveals, surprisingly, a stable correlation between the magnetic activity index A _P and the oceanic part in the horizontal and vertical components but not in declination, which probably indicates the influence of induced currents, along the latitudes, on L _o.     

Evidence for warmer event from quartz grains in the soil of Grove Mountains,East Antarctica

<正> The cold desert soil has been discovered at first time in southern ridge ofMount Harding,Grove Mountains of interior East Antarctica Ice Sheet.Based on themicro structural observation,dominant characteristics of quartz grains include:dis-tinct surface stria and fractures,and clean features of frost action at both of crystalmargins and micro crannies of quartz grains.These features show a pedogenesis envi-ronment of few water,short transportation and frost action,revealing a warmer climat-ic event existed in this region.     

1992–2015全球耕地时空变化（英文）

人口和人均食物需求的增加对全球耕地产生了显著的影响。利用欧空局提供的精度为300m的最新土地覆被产品,文章分析了1992-2015年全球耕地的时空变化趋势和耕地转化特征。结果显示:1)在1992-2004年间全球耕地面积增长迅速,而在2004-2012年间耕地增长缓慢,2012年后耕地有缓慢减少的趋势。2)在洲尺度上,非洲耕地有一直增长的态势,而其他洲耕地都经历了耕地转型,有先增长后下降的趋势;在收入较高的国家,耕地多有下降的趋势。3)全球耕地增长的热点区域主要分布在亚马逊林地、欧亚大草原和撒哈拉沙漠边缘。全球耕地减少的中心从欧洲转移到亚洲。由于迅速的城市化,亚洲耕地扩张侵占了大量农田。     

Spatial and Temporal Variation of Cropland at the Global Level from 1992 to 2015

Correlated increases in population and demand for food over recent decades have caused remarkable changes in cropland area globally. Utilizing the latest data product provided by the European Space Agency (ESA), this paper analyzes annual trends and spatiotemporal variations in cropland area and discusses cropland conversion, losses, and increases globally between 1992 and 2015 at a 300 m resolution. The results show that the global area of cropland increased rapidly between 1992 and 2004, more slowly between 2004 and 2012, and began to decrease gradually since 2012. First, an increasing trend in cropland area has been maintained solely in Africa; all other regions are characterized by decreasing trends in later periods despite different transition points and change rates. A reduction in cropland area frequently emerged earlier in high-income countries. Second, increase rates in cropland area have largely decreased in recent years while the overall rate of loss has remained almost the same. Hotspot areas of global cropland increases are mainly concentrated around the edge of the Amazon forest, Eurasian Steppe, and Sahara Desert. These hotspot areas of global cropland loss shifted from Europe to Asia while built-up areas have expanded at the expense of cropland.