Study on the Anomaly of Small Earthquake Activity Before Moderate-strong Earthquake in the Northeast Margin of the Qinghai- Xizang （Tibet） Block

26 earthquakes with MS ≥5. 0 have been recorded in the northeast margin of the Qinghai- Xizang (Tibet) block since 1980,22 of which were relatively independent of other moderate- strong earthquakes. Research on the increase of small earthquake activity before the 22 moderate-strong earthquakes has indicated that small earthquake activity was enhanced before 17 of the moderate-strong earthquakes. Though the increased seismicity is a common phenomenon in the northeast margin of the Qinghai-Xizang ( Tibet ) block,we have difficulty in predicting the moderate-strong earthquakes by this phenomenon. In order to predict the moderate-strong earthquakes through the increased seismicity of small earthquakes,this paper attempts to propose a new method, which calculates small earthquake frequency through the change of distribution pattern of small earthquakes, based on the characteristics of small earthquake activity in the northeastern Qinghai-Xizang (Tibet) block,and then make primary applications. The result shows that we are able to obtain obvious anomalies in the frequency of small earthquakes before moderate strong earthquakes through the new method,with little spatial range effect on the amplitude of this small earthquake frequency anomaly. We can obtain mid to short-term anomaly indices for moderate-strong earthquakes in the northeast margin of the Qinghai-Xizang (Tibet) block.     

Discovery of the Surface Rupture Zone on the South of Helishan in Gaotai,Gansu Province

According to a new investigation in the northern Hexi corridor,the remains of two surface rupture zones were discovered on the southern margin fault of the Helishan. One rupture has a length of approximately 7km and the other 10km. The two surface rupture zones might have been produced by the latest earthquake event. On the surface rupture is continuous scarp and free face caused by the rupture. The scarp is about 1 ～ 1. 5m high and on some sites,nearly up to 2m. According to the OSL results,the latest T1 terrace and higher flood plain forming in 3000a B. P. are dislocated by the fault. The above reveals the rupture age to be later than the T1 terrace. However,in the historical data and earthquake catalogue,we didn't find related information about the fault and surface rupture in this area. The 180 A. D. Biaoshi M8. 0 earthquake and the 756 A. D. Zhangye-Jiuquan M7. 0 earthquake are documented in historical data. It is inferred by textual research that the two earthquakes are related to the northern marginal fault of Yumushan in the south of the basin. Due to a lack of reliable evidence,there are still many arguments on this inferred conclusion. Thus we hold that the two surface rupture zones were produced by one of the two large earthquakes or other unrecorded historical event. The research on the activity and surface rupture of this fault can offer valuable information for the tectonic study and strong earthquake risk estimates of this region in the future.     

High resolution transmission electron microscopy evaluation of silica glaze reveals new textures

We present the first nanoscale investigation of silica glaze. High resolution transmission electron microscopy of a rock coating from the Ashikule Basin, Tibetan Plateau, reveals the presence of spheroids composed predominantly of silicon and oxygen with diameters ranging from 20 nm to 70 nm. While silica glaze spheroids co‐exist with manganese‐rich rock varnish in the same sample, the different rock coatings are texturally and physically distinct at the nanoscale. These observations are consistent with a model of silica glaze formation starting with soluble aluminum‐silicon (Al‐Si) complexes [Al(OSi(OH)³)²⁺], mobilized with gentle wetting events such as dew or frost. The transition between complete and partial wetting on silica surfaces rests at about 20–70 nm for liquid droplets. Upon crossing this transition, a metastable wetting film would be ruptured, initiating formation of silica glaze through spheroid deposition. Copyright © 2010 John Wiley & Sons, Ltd.     

Seasonal variations and trophic ecology of microzooplankton in the southeastern Arabian Sea

The seasonal ecological response of microzooplankton in the southeastern Arabian Sea is presented. During the spring intermonsoon period, stratification and depletion of nitrate in the surface waters (nitracline was at 60 m depth) cause low integrated chlorophyll a (av. 19±11.3 mg m⁻²) and primary production (av. 164±91 mgC m⁻² d⁻¹). On the other hand, nutrient enrichment associated with coastal upwelling and river influx during the onset and peak summer monsoon resulted in high integrated chlorophyll a (av. 21±6 mg m⁻² and av. 29±21 mg m⁻², respectively) and primary production (av. 255±94 mgC m⁻² d⁻¹ and av. 335±278 mgC m⁻² d⁻¹, respectively). During all three periods, diazotropic cyanobacterium Trichodesmium erythraeum dominated in the nutrient depleted surface waters. A general increase in abundance of larger diatoms was evident in the surface waters of the inshore region during monsoon periods. The microzooplankton abundance was found to be significantly higher during the spring intermonsoon (av.241±113×10³ ind m⁻²) as compared to onset of summer monsoon (av. 105±89×10³ ind m⁻²) and peak summer monsoon (av.185±175×10³ ind m⁻²). Microzooplankton community during the spring intermonsoon was numerically dominated by ciliates while heterotrophic dinoflagellate was the dominant ones during the monsoon periods. The high abundance of ciliates during the spring intermonsoon could be attributed to the stratified environmental condition prevailed in the study area which favors high abundance of smaller phytoplankton and cyanobacteria, the most preferred food of ciliates. On the other hand, the dominance of heterotrophic dinoflagellates during the monsoon periods could be linked to their ability to graze larger diatoms which were abundant during the monsoon periods. The overall results show low abundance of microzooplankton in the eastern Arabian Sea during the monsoon periods mainly due to a decline in ciliates abundance. This decline during the monsoon periods could be the result of (a) low abundance of smaller phytoplankton and (b) high stock of mesozooplankton predators (av. 245 ml 100 m⁻³).     

利用中国地震科学台阵研究青藏高原东南缘地壳各向异性:第一期观测资料的剪切波分裂特征

中国地震科学台阵第一期(2011—2013年)布设在南北地震带南段,本研究利用中国地震科学台阵布设在云南及相邻地区的部分流动台站记录到的2011年6月至2013年3月的数字地震波形资料,开展地壳各向异性分析.本文使用剪切波分裂系统分析方法(SAM方法),获得了研究区内67个台站的剪切波分裂参数.研究结果表明,受到云南及周边地区复杂的构造、应力环境和纵横交错的断裂分布的影响,该地区快剪切波偏振方向(PAZ)整体上显示出NNE向和NE向的优势取向,但在空间分布上比较复杂,虽然大部分台站的PAZ与构造应力场方向一致,但部分断裂附近台站的PAZ受到断裂的影响.结果显示,本研究区内不同区域的PAZ有一定差异性.本研究划分了5个子区,西部3个不同区域的PAZ从北到南分别为NNW向、近N-S向和NE向,有顺时针旋转的趋势,而东部的2个区域PAZ分别为NEE向和NNW向.研究证实,青藏东南缘地区的地壳各向异性空间分布虽然非常复杂,但大体上与区域内的主压应力的方向和断裂分布相关.     

Petrogenesis of diabase from accretionary prism in the southern Qiangtang terrane,central Tibet: Evidence from U–Pb geochronology,petrochemistry and Sr–Nd–Hf–O isotope characteristics

The Bangong–Nujiang suture (BNS) between the Lhasa and Qiangtang terranes is an important boundary and its petrogenesis is controversial. Diabase from the accretionary prism in the southern Qiangtang terrane yields a zircon U–Pb age of 181.3 ± 1.4 Ma. All the diabases show tholeiitic basalt compositions, gentle enrichment patters of light rare earth elements (REE), variable enrichment in incompatible element concentrations (e.g. Th and Rb), and no anomaly in high field strength elements (e.g. Nb and Ta), similar to that of enriched mid‐ocean ridge basalt (E‐MORB). They have relatively homogeneous whole rock Nd (εNd(t) = 7.3–9.1) and zircon Hf–O isotopic compositions (εHf(t) = 14.8–16.1, and δ¹⁸O = 4.57–6.12‰), possibly indicating melting of the depleted mantle and no significant crustal contamination during the petrogenesis. The element variations suggest that the diabases were formed by plume–ridge interaction at a mid‐ocean ridge within the Bangong–Nujiang ocean.     

西藏NPP时空格局与气候因子的关系

根据2000-2012年1 km MOD17A3 NPP遥感数据和气温、降水等气象资料,在GIS支撑下,结合多种统计计算方法,对西藏NPP时空格局与气候因子的关系进行研究。结果表明:2000-2012年间西藏陆地植被的NPP为119.3～148.4 g·m^-2·a^-1,平均为135.2 g·m^-2·a^-1;近年来西藏NPP呈不显著上升趋势,NPP总体上由东南向西北逐渐变小。13年来西藏NPP在总体不变(面积占61.11%)的基础上略有增加(面积占10.7%);不同植被类型中阔叶林的NPP最大,为1 185.2～1 430.2 g·m^-2·a^-1,其次是混交林,为535.1～741.2 g·m^-2·a^-1,其后依次是稀树草原、针叶林、农用地、草地和灌丛;西藏NPP与气温、降水因子分别有较好的正、负相关性。所有植被类型都与年均气温呈正相关,其中草地的NPP与年均气温的相关系数达0.88,其次是针叶林为0.76,相关性最差为热带稀树草原0.13;与年降水量的相关性,除了热带稀树草原正相关(0.26),其余都负相关,草地、针叶林的相关系数分别为-0.79、-0.73。     

气候变化对藏东北牧业生产关键期的影响

利用藏东北10个气象站1961-2013年逐日平均气温资料,采用反距离权重插值法、线性回归、Mann-Kendall检验等方法,分析了牧草生长季(PGS)、牧草青草期(GGD)、牲畜抓膘期(FD)和牲畜掉膘期(FLD)等牧业生产关键期的时空变化,预估了未来50 a和100 a牧业生产关键期的变化.结果表明:近53 a PGS因结束日推迟而延长1.70 d·(10a)^-1,GGD平均每10 a延长1.53 d,牲畜抓膘开始期线性趋势不明显,结束期趋于推迟,FD平均每10 a延长1.84 d;牲畜掉膘开始日期显著推迟,结束日明显提前,FLD以-4.33 d·(10a)^-1的速度显著缩短.PGS的变化趋势与经度呈正相关,与海拔高度为负相关.PGS突变发生较早,出现在1998年;2005年是GGD明显变长的突变点,而FD和FLD的突变时间均发生在2003年.在10 a年际变化尺度上,近30 a PGS、GGD和FD呈逐年代增加趋势,而FLD趋于减少.如果气候按升温率0.044℃·a^-1变化,50 a后PGS、GGD和FD分别延长20.2、18.4和21.6 d,FLD缩短23.2 d;未来100 a PGS、GGD和FD可能分别延长40.3、36.9和43.2 d,FLD缩短46.5 d.这种变化趋势十分有利于藏东北牧草生产.     

西藏埃永错东地区区调成果与展望

根据1:5万区域地质调查有关规范和技术要求,在西藏埃永错东地区开展了1:5万区域地质调查。通过对岩石地层、年代地层、生物地层、层序地层和事件地层等多重地层的划分与对比,重新厘定了古生代、中生代地层形成的时代和地层序列,并将特殊岩性层以非正式填图单位进行了表达; 系统查明了区域地层、岩石、构造特征和成矿地质条件; 首次在晚三叠世日干配错群中新识别出晚侏罗世-早白垩世雪山组; 建立了测区二叠系多重地层划分方案; 重新厘定了日干配错群基本层序和物质组成,将日干配错群进一步划分为2个组; 新解体出31个侵入体、8个潜火山岩地质体和多条中酸性脉体; 查明了区内断裂、褶皱等构造性质、时代、序次及空间配置关系,建立了测区构造格架和构造样式; 新发现金属矿（化）点18处,找矿靶区2处。     

青藏高原东北缘若尔盖盆地黄土的成因

通过对盆地黄土的粒度组分、石英砂的表面结构以及其它地质现象的综合研究,对若尔盖盆地黄土成因进行了探讨.在黄土的概率累计曲线上,跃进组分和悬移组分反映明显,以悬移组分为主,并采用矩阵法计算了黄土的粒度参数.对黄土扫描电镜观察和石英颗粒表面特征的统计分析,反映出气流搬运的特点,以发育碟形坑为其主要标志,具有风成环境的表面特征组合.黄土中孢粉稀少,并在邻区黄土层中发现有冰楔构造.根据上述特征分析出,若尔盖盆地黄土应为冰缘风成黄土.以测年资料为依据,黄土形成年代主要为马兰期茶镇梁子黄土和离石期索克藏寺黄土.