北阿尔金地区古元古代岩体LA-ICP-MS锆石U-Pb年龄及其地质意义

北阿尔金是塔里木克拉通变质基底的主要出露区之一。对该区具有侵入接触关系的正长花岗岩和花岗片麻岩进行了LA-ICP-MS锆石U-Pb定年研究。正长花岗岩中的锆石多呈椭圆状,具有振荡环带结构,部分颗粒中可见老锆石残核,Th/U值较高,亏损轻稀土元素,富集重稀土元素,具有负Eu异常和正Ce异常的特点,表明该组锆石为岩浆成因。定年结果获得1903±13Ma和2506±55Ma两组年龄加权平均值,前者代表岩体的结晶年龄,后者为捕获锆石年龄,结合区域年代学资料,认为正长花岗岩岩浆侵入过程中可能捕获了太古宇米兰群的古老基底锆石。花岗片麻岩中16个测点的锆石~(207)Pb/~(206)Pb年龄集中于1802±28Ma,代表了岩体侵位时代,其余5个测点的锆石~(207)Pb/~(206)Pb年龄为1911~1951Ma,说明岩浆侵位过程中捕获了部分正长花岗岩的物质。区域地质与同位素年代学研究表明,北阿尔金地区广泛存在2.0~1.8Ga的构造-热事件。获得的花岗质岩石的1.9~1.8Ga的年龄结果,直接证实了北阿尔金存在约1.9Ga的岩浆作用,可能为古元古代Columbia超大陆汇聚事件在该地区的响应,为探讨塔里木板块前寒武纪构造-热事件演化历史提供了新资料。古元古代末期约1.8Ga的花岗片麻岩,代表了后造山伸展阶段的岩浆活动。     

西沙海域南部多边形断层的发现及其分布特征与控制因素

根据新采集的三维地震资料,在西沙海域南部发现了多边形断层,其发育分布具有层控特征明显、在富泥地层中发育、多方位走向、纵向断距小、平面延伸长度小且形态为不规则多边形等特征。由于研究区东西两侧应力条件的差异,导致多边形断层发育特征的差异明显。通过对多边形断层发育控制因素的分析,认为地层岩性(特别是西沙海域上构造层的远源细粒沉积物)是其发育的主控因素之一,同时水道砂岩、成岩作用及构造作用等也是影响其发育分布的因素。多边形断层可以作为流体运移的通道,它与下部构造断层连接可将深部烃源岩中的油气运移到上部储层中聚集,或继续向上运移到浅部地层中形成天然气水合物。     

A numerical simulation of impact of groundwater seepage on temperature distribution in karst collapse pillar

This paper presents an investigation of the impacts of groundwater seepage on temperature distribution in the karst collapse pillar (KCP). A thermal mathematic model with groundwater seepage was proposed, and a numerical model was established to describe the impacts of groundwater seepage on the temperature distribution in the KCP. The results show that the groundwater seepage velocity improved with the increasing permeability of porous medium in the KCP. The increasing seepage velocity improves thermal convection and then improves thermal conduction in the porous medium. As a result, the heat in the deep Ordovician limestone groundwater gradually diffuses. The seepage velocity occurred differently in different locations of KCP, and the heat exchange was also different, resulting in temperature differences for different locations. This temperature divergence in the surrounding rocks can reach 5~9°C at distances less than 50 m to the KCP. These findings can be used to protect the mine from water inrush by monitoring temperature changes in the surrounding rocks of KCP.     

Seismic vulnerability assessment in the new urban area of Diriyah Governorate,Riyadh, Saudi Arabia

Nine seismic refraction profiles were conducted and processed to study the near-surface sediments in the new urban area of Diriyah. The 2D geoseismic models illustrate two layers: a surface layer of soft sediments and weathered to hard limestone bedrock. Moreover, microtremor measurements were performed at 38 sites for 40 min using three-component seismographs and processed to assess the peak spectral amplitude and the corresponding fundamental resonance frequency. The seismic vulnerability index at each measurement site was estimated. These results correlate well with the geotechnical borehole data. The north-western zone is highly vulnerable due to the great thickness of the soft sediments.     

维嘉海山沉积过程及其对西太平洋海山演化的意义

海山沉积过程与全球气候变化和古海洋演化有着紧密联系,维嘉海山保留了西太平洋晚中生代以来的完整沉积记录,是探索西太平洋海山构造演化的理想场所.基于浅地层剖面、大洋钻探和最新相关研究成果,通过研究海山的沉积特征、火山活动和沉降速率等,探索西太平洋维嘉海山晚中生代以来的沉积过程.结果显示维嘉海山顶部发育3个沉积单元,并发现了...     

利用Landsat时序NDVI数据进行新疆石河子垦区灌溉作物分类

精确的农作物分类信息对于农业环境评估、水资源利用规划非常重要,尤其是在干旱、半干旱地区。本文利用30 m分辨率的Landsat NDVI时间序列数据进行了新疆石河子垦区混合农作物精确区分的潜力研究。首先利用S-G滤波重构了Landsat NDVI时间序列,然后基于SVM模型对研究区域农业类型进行了精确分类。在SVM分类模型作用下,S-G重构后的时间序列有效地将该地区棉花、玉米、小麦等主要作物区分开来,精度高于0.86,Kappa系数大于0.82。结果表明,S-G滤波能够有效提高NDVI时间序列数据质量;TM影像时间序列在监测干旱、半干旱地区的作物类型和种植方式随时间的变化方面存在巨大潜力。     

Effective ellipsoidal models for wavefield extrapolation in tilted orthorhombic media

Wavefield computations using the ellipsoidally anisotropic extrapolation operator offer significant cost reduction compared to that for the orthorhombic case, especially when the symmetry planes are tilted and/or rotated. However, ellipsoidal anisotropy does not provide accurate wavefield representation or imaging for media of orthorhombic symmetry. Therefore, we propose the use of ‘effective ellipsoidally anisotropic’ models that correctly capture the kinematic behaviour of wavefields for tilted orthorhombic (TOR) media. We compute effective velocities for the ellipsoidally anisotropic medium using kinematic high-frequency representation of the TOR wavefield, obtained by solving the TOR eikonal equation. The effective model allows us to use the cheaper ellipsoidally anisotropic wave extrapolation operators. Although the effective models are obtained by kinematic matching using high-frequency asymptotic, the resulting wavefield contains most of the critical wavefield components, including frequency dependency and caustics, if present, with reasonable accuracy. The proposed methodology offers a much better cost versus accuracy trade-off for wavefield computations in TOR media, particularly for media of low to moderate anisotropic strength. Furthermore, the computed wavefield solution is free from shear-wave artefacts as opposed to the conventional finite-difference based TOR wave extrapolation scheme. We demonstrate applicability and usefulness of our formulation through numerical tests on synthetic TOR models.     

用连续GPS与远震体波联合反演2015年尼泊尔中部M_S8.1地震破裂过程

由于印度-欧亚板块碰撞,位于板块边界带的喜马拉雅地区大震频繁,但对其活动性的认识仍十分有限.2015年4月25日尼泊尔中东部地区时隔80年再次发生8级地震,为研究板缘地震提供了一次难得机遇.本文用西藏和尼泊尔的GPS连续观测数据和全球分布的远震地震波记录联合反演此次特大地震的破裂过程,结果显示此次地震发生在印度板块与青藏高原接触边界面——喜马拉雅主滑脱断层上.北倾11°、近东西(295°)走向的断层面破裂约100km长(博卡拉到加德满都),130km宽(从加德满都深入我国西藏吉隆县),破裂以逆冲滑动为主,平均幅度达到2.4m,释放的地震矩高达9.4×1020 N·m.反演结果还显示,震源体主要破裂分布深度范围为5~25km,应无地表破裂,属于一次盲地震.基于GPS资料推测的地壳现今运动速率及1833年地震的震源位置,我们推测地震在此次地震破裂区域复发的周期可能为150~200a,而极震区以南的深部滑脱断层仍保持闭锁,未来仍有导致灾害性大震的可能性.     

塔里木河流域TRMM降水数据精度评估

利用塔里木河流域24个气象站降水数据,分析了2000-2013年TRMM多卫星降水数据(TRMM 3B43 v7)在塔里木河流域的适用性。检验结果表明:全年来看,TRMM数据对研究区所有站点的年均降水量拟合较好(R²=0.8846),流域内24个站点平均年降水量相对偏差为19.02%,其中60%的站点表现为TRMM年降水量高于地面实测年降水量;月降水方面,除个别站点(于田、且末、乌恰)较差外,大部分站点的拟合度都较好;就季节而言:春季拟合效果最好,夏、秋季的TRMM数据存在低估问题,而冬季则偏高估;流域降水量由东南向西北递增,并在西北部边缘地区增加较显著,形成一个相对丰水带;而向沙漠腹地方向延伸的降水量则呈减少趋势。同时流域最大降水区域在一年中变化存在一定的规律。     

基于地理探测器的北京市居民宜居满意度影响机理

城市宜居性是与居民生活质量密切相关的科学议题,深入探讨宜居满意度影响机理对把握转型期北京市居民居住环境需求、促进宜居城市建设等具有重要的现实意义。以北京市为案例,基于2013年宜居城市大规模问卷调查数据,运用因子分析方法提取了北京市居民宜居满意度主要感知因素,并分别从居民宜居感知因素、个体与家庭属性因素两个视角,借助地理探测器方法揭示了北京市居民宜居满意度特征与影响机理。研究发现：①北京市居民宜居满意度主要由污染噪声因子、生活设施因子、人文环境因子、出行便捷因子、自然环境因子、安全环境因子和休闲活动因子等7个维度构成。②宜居满意度受到宜居感知因素和个体与家庭属性共同影响,但宜居感知因素的解释力明显要强,其中污染噪声因子、自然环境因子和出行便捷因子等因素是关键因子。③宜居满意度与宜居感知因素具有相对一致性,且存在个体与家庭属性差异。通常宜居感知因素得分低居民,其宜居满意度也相对较低;另外,远郊区、租赁房、有迁居经历、男性、30~39岁、高中学历、家庭月收入5000元以下和外地户口等社会群体的宜居满意度明显要低。