综合石油地质、历史地震等资料评估吉林孤店隐伏断裂的地震危险性

在对松原地区开展的活断裂探测工作中发现了一条晚更新世活动断裂,称之为孤店断裂。本文通过三维地震资料获得了孤店隐伏活动断裂的地下细部结构,在对其地质构造、第四纪活动性、历史地震记录及地震活动性等进行综合研究的基础上,采用石油物探三维地震资料获得的基岩破裂长度进行经验关系拟合,对其潜在地震最大震级进行了评估,评估结果认为其约为M_W7。此外,采用地震矩方法获得复发周期、年发生率等定量参数,利用中国大陆古地震复发概率模型估算出孤店断裂未来50~200a的大地震发生概率。     

Expansion of the Cathaysian Oldland through the Ordovician-Silurian transition:Emerging evidence and possible dynamics

Located northwest of the Jiangshan-Shaoxing Fault Zone,western and northwestern Zhejiang and northeastern Jiangxi provinces experienced major changes in bio-and litho-facies and paleogeography through the Ordovician-Silurian transition (late Katian,Hirnantian,and early Rhuddanian),as manifested by stratigraphic,paleontologic and synecologic records.Three geographic units under consideration are South,Central,and North areas.The western margin of the South area was occupied by the Huaiyu Mountains,whereas th...     

Response of underground pipeline through fault fracture zone to random ground motion

It is assumed that a pipeline is laid through a vertical fault fracture zone, and is excited by seismic ground motion modelled as stationary stochastic process. For horizontal incidence of waves, the cross-PSD (Power Spectral Density) function is developed using wave propagation theory, while for vertical incidence of waves the cross-PSD function is composed by auto-PSD model, coherence model and site response model. As the seismic input, the cross-PSD function is used to calculate the the axial and lateral seismic responses of underground pipeline through the fracture zone. The results show that the incident directions of seismic waves, width and soil property of the fracture zone have great influence on underground pipeline. It is suggested that the flexible joints with appropriate stiffness should be added into the pipeline near the interfaces between the fracture zone and the surrounded media.     

Geochemical signature of porphyries in the Baogutu porphyry copper belt, western Junggar, NW China

The Baogutu porphyry copper belt lies in the Darbut transitional island arc of the western Junggar, in the western section of the Central Asian Orogenic Belt in NW China. Our new petrographic results for the ore-bearing porphyry stocks in the Baogutu porphyry copper belt recognize them as diorite porphyry stocks rather than the granodiorite porphyry stocks as previously identified. The copper mineralization is hosted in the diorite, diorite porphyries and related breccias of the diorite porphyry stocks.Geochemical data indicate that the ore-bearing porphyries have a predominantly intermediate composition with a transitional character from tholeiite to calc-alkaline, and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) with a clear negative Nb anomaly. REE patterns show distinct enrichments in LREE relative to HREE. The rocks also exhibit high initial εNd(t) (+ 2.7 to + 6.3) ratios and low initial ⁸⁷Sr/⁸⁶Sr values (0.70359–0.70397). Many samples are chemically similar to adakites (e. g. Yb < 1.9 ppm, Y < 18 ppm, Sr/Yb > 20, ⁸⁷Sr/⁸⁶Sr < 0.7045). These data are consistent with a transitional island arc from immature arc to mature arc and suggest that the ore-bearing porphyry system was derived from the partial melting of multiple sources including oceanic crust and a subduction-modified mantle wedge, with melts undergoing significant crystal fractionation during convergence between the paleo-Junggar ocean and the Darbut arc.     

东秦岭中生代钼铅锌银多金属矿床模型及其找矿评价

最近几年不仅在东秦岭地区又发现和探明一批大型—超大型斑岩型钼矿床,而且在南泥湖矿田（包括南泥湖-三道庄-上房沟矿床）和东沟超大型斑岩钼矿床外围探明了一批脉状铅锌银矿。这些脉状铅锌银矿与斑岩钼矿具有明显的时空关系,而且互为找矿指示。以南泥湖和东沟为代表的斑岩钼矿分别形成于晚侏罗世—早白垩世（156~137Ma）和白垩纪中期（125~114Ma）,其成矿有关岩体指示成矿物质分别来源于壳幔同熔和壳源。尽管有物质来源的差别,但是在2个不同时代斑岩钼矿的外围都有一系列脉状铅锌矿的发育,而且通常在断裂膨大或拐弯处和2组断裂的交会部位形成大矿和富矿,也见出现在地层不整合界面的部位。这种钼与铅锌矿的密切时空分布关系构成一个很好的成矿系统,斑岩－矽卡岩钼矿与铅锌银矿互为找矿的指示标志。矿床模型的建立有利于进一步推动在中国东部地区开展此类矿床组合的找矿勘查。     

近50年中国西北东部半湿润、半干旱过渡带气候变化及生态影响

以宝鸡、凤翔、千阳、陇县、西峰、环县、平凉、泾源、六盘山、固原市、西吉和海原等台站的气象数据为依据,对近50年来地处西北地区东部的半湿润、半干旱过渡带的气候要素进行了系统分析,发现区内各地气温有普遍升高的趋势。其中,冬季升温趋势更加明显。各地在20世纪90年代前后发生气温突变,以此为界,前后增加速度明显不同,此后的增温趋势明显加快。近50年以来,各地降水略有下降,主要是由夏季降水减少所引起,但是统计趋势不明显。受气温和降水变化综合影响,区域气候向变干和变暖的方向发展。根据Holdridge生命地带理论,初步分析了区域植被与气候之间的关系。计算表明,最近30年以来,西北东部半湿润、半干旱区过渡带的气候变化使区域植被也向干暖化类型变化。位于研究区中部的六盘山、泾源和西吉等地生命地带类型的变化都比较大。崆峒山(35°33′N,106°31′E)的圆柏(Sabina chinensis)树轮气候学分析表明,区域树木生长与前一年秋季降水呈显著正相关关系,与当年春季和夏季气温呈显著负相关趋势,说明生长季的缺水或高干燥度是树木生长的限制性因素。研究时段区域干旱频繁发生,使树木出现大量伪轮,为研究带来一定难度,但是也进一步验证了区域气候变化的干旱特征。干燥指数重建结果表明,研究区在20世纪20年代比较干旱,30年代是相对较为湿润的时期; 1940年和1960年左右较为干旱,但其间的干燥指数较低。60年代之后,区域干燥指数逐渐增加,表明干旱趋势日趋加重,与气象数据分析结果相一致。事实证明,研究区气候的干暖化变化对区域树木生长和生态系统具有非常不利的影响。     

黄土高原黄土物源区的同位素证据

系统采集了黄土高原马兰黄土、河西走廊和青藏高原东北部黄土、河床沙和湖泥样品。用酸淋洗去除方解石后,黄土高原马兰黄土εNd(0)值从-9.2到-11.3,87Sr/86Sr比值从0.71784到0.71944,都落在同位素B区内,与青藏高原东北部、巴丹吉林沙漠和腾格里沙漠的值一致。黄土高原马兰黄土白云石的δ13C值从1.2‰到1.5‰,与青藏高原东北部和河西走廊黄土,巴丹吉林沙漠的白云石的值类似。这些表明青藏高原东北部、巴丹吉林沙漠和腾格里沙漠可能是黄土高原黄土的源区,从而排除了其他沙漠(古尔班通古特沙漠、塔克拉玛干沙漠、毛乌素沙漠、库布齐沙漠、浑善达克沙地、科尔沁沙地和呼伦贝尔沙地)作为黄土物源区的可能性。同位素研究结果和野外调查进一步揭示,黄土高原黄土、巴丹吉林沙漠和腾格里沙漠物质可能最终都是来源于青藏高原东北部。     

THE FORMATION AND DEVELOPMENT OF A MESOSCALE CONVECTIVE SYSTEM WITH HEAVY RAINFALL ALONG SOUTH CHINA COASTAL AREA

Observational analysis shows that a Mesoscale Convective System (MCS) occurred on May 13- 14 2004 along the coastal area in South China. The MCS initiated among the southwesterly flows within a west-east orientation low-level shear line. Associated with the system, in its subsequent development stages, no distinct vortex circulation developed in low-level. Instead, a cyclonic flow disturbance was observed in the mid-troposphere. How the convection starts to develop and evolve into a MCS? With observational analysis and numerical simulation, the problem has been studied. The high-resolution MM5 simulation shows that topographic convergence along the coastal line and the nearby mountains in western South China plays an important role to initiate the MCS convection. Once the convection occurs, due to the condensation heating, a cooperative interaction between the preexisting mid-level disturbance and convection is created,which may greatly affect the MCS development during periods when the system continues moving eastward.Compared to some typical MCS that happen in Southern China, which are usually accompanied with upward development of cyclonic vorticity, the development and evolution of the investigated MCS shows distinguishing features. In this article, the physical mechanisms responsible for the intensification of mid- level disturbance are discussed, and a viewpoint to interpret the effects of mid-level disturbance on the MCS organizational development is proposed.     

Geometric structure and formation mechanism of Lintong-Chang’an fault zone

The results from investigation of large quantity of fault outcrops and artificial earthquakes suggest that the Lin-tong-Chang’an fault zone mainly consists of two faults. One is the Majie-Nianwan fault that separates a branch of Wangjiabian-Houjiawan fault on the right bank of the Bahe River; the other is the Hujiagou-Shoupazhang fault that separates a branch of Zhongdicun-Tangjiazhai fault in Tongrenyuan and Shaolingyuan. As tensional dip-slip normal faults, the faults distribute with approximately parallel equal intervals in local regions and the profiles drop in a step-like form to the northwest, presenting a Y-shape combination. The result from deep seismic reflection indicates that the fault is about 5~8 km in depth, which is not only a basement fault, but also a listric normal fault in the deep stratum. The Lintong-Chang’an fault is a typical outstretching rift system under the NS-trending ten-sion stress field. At the same time, affected by the sinistral strike slip of the Yuxia-Tieluzi fault, the fault extends like a broom from the northeast to the southwest.     

甘肃年度地震危险区划定的R值评分研究

年度地震危险区是一个比较特殊的评价对象.作者在前人研究的基础上对R值评分公式做了适当的改进,将原有方法的用地震个数求报准率,改为用地震危险区面积求取报准率,在不改变公式物理意义的前提下,使其更适合于对年度地震危险区这个特殊对象做出科学评价.改进后的公式排除了数学上不成立的情况,不鼓励虚测,不鼓励漏测.对甘肃1986～2007年的年度地震危险区和目前甘肃地震预测预报水平做出了科学客观的评价.依据评价结果提出了改进年度地震危险区划定方法的建议.