Spatiotemporal Pattern and Driving Force Analysis of Vegetation Variation in Altay Prefecture based on Google Earth Engine

Quantitative evaluation and driving mechanism analysis of vegetation dynamics are essential for promoting regional sustainable development. In the past 20 years, the ecological environment in Altay Prefecture has changed significantly due to global warming. Meanwhile, with increasing human activities, the spatiotemporal pattern and driving forces of vegetation variation in the area are uncertain and difficult to accurately assess. Hence, we quantified the vegetation growth by using the Normalized Difference Vegetation Index (NDVI) on the Google Earth Engine (GEE). Then, the spatiotemporal patterns of vegetation from 2000 to 2019 were analyzed at the pixel scale. Finally, significance threshold segmentation was performed using meteorological data based on the correlation analysis results, and the contributions of climate change and human activities to vegetation variation were quantified. The results demonstrated that the vegetation coverage in Altay Prefecture is mainly concentrated in the north. The vegetation areas representing significant restoration and degradation from 2000 to 2019 accounted for 24.08% and 1.24% of Altay Prefecture, respectively. Moreover, spatial correlation analysis showed that the areas with significant correlations between NDVI and temperature, precipitation and sunlight hours accounted for 3.3%, 6.9% and 20.3% of Altay Prefecture, respectively. In the significant restoration area, 18.94% was dominated by multiple factors, while 3.4% was dominated by human activities, and 1.74% was dominated by climate change. Within the significant degradation area, abnormal degradation and climate change controlled 1.07% and 0.17%, respectively. This study revealed the dynamic changes of vegetation and their driving mechanisms in Altay Prefecture, and can provide scientific support for further research on life community mechanism theory and key remediation technology of mountain-water-forest-farmland-lake-grass in Altay Prefecture.     

大角度P-P波反射系数近似方法研究

Zeoppritz方程的近似形式大多是符合小角度或中等角度入射条件的,大角度入射时的近似公式很少.因此,从精确的纵波反射系数计算公式出发,推导纵波在大角度入射时纵波反射系数近似计算公式,该公式以射线参数P及垂直慢度qa1,qa2,纵横波速度Vp,Vs为参数.由于在大于临界角时,反射系数变为复数,公式采用分段表示,一部分...     

川中合川地区上三叠统须家河组二段储层特征

合川地区须家河组二段显示出较好的含油气性,通过对该地区岩心及铸体薄片观察分析,对该区须家河组二段的沉积相、岩石学特征、孔喉结构、成岩作用、物性特征及其主控因素进行了深入研究.认识到合川地区须二段岩性主要为岩屑长石砂岩和长石岩屑砂岩,属于三角洲前缘亚相沉积,水下分流河道和河口砂坝是主要储集砂体,储集空间类型主要为粒间孔和粒内溶孔,并搞清了合川地区须二段储层的成岩作用、物性特征及其控制因素,对加快合川地区须二段的勘探开发步伐具有重要的理论价值和现实意义.     

Diagenesis of sandstones in the back-arc basins of the western Pacific Ocean

ABSTRACT Sandstones occur in back-arc basins of the western Pacific at DSDP sites 299 (Sea of Japan), 297 (northern Shikoku Basin), 445 and 446 (Daito-Ridge-and-Basin Province), 453 (Mariana Trough), 286 (New Hebrides Basin) and 285 (South Fiji Basin). These sandstones are dominantly volcaniclastic arenites derived from andesitic island arcs. The degree of sandstone diagenesis is dependent on original composition, burial rate, heat flow history of the basin, and timing of sandstone deposition with respect to rifting processes and associated high heat flow.
Sandstones containing a larger proportion of volcaniclastic components showed more diagenetic effects than sandstones containing a significant volume of other rock fragments and mineral components. Sandstones deposited during early stages of rifting (sites 445, 446) with a slow burial rate and high crustal heat flow showed the greatest degree of downhole diagenetic change. These diagenetic changes include early pore-space reduction and rim cementation by clay minerals followed later by calcite, and subsequent pore-fill cementation by clinoptilolite, heulandite, analcite and later calcite. Replacement of recognizable volcanic rock fragments by chert, calcite and zeolites was observed in the deepest part of the hole. Sandstones deposited after rifting under conditions of associated lower heat flow showed considerably less diagenetic changes, particularly if burial was rapid.
The high heat flow associated with earliest rifting, associated fluid circulation driven by thermal convection, and slow burial rate controlled the diagenetic history of these sandstones. Thus, timing of sandstone deposition with rifting stage and associated burial rates were key factors in controlling sandstone diagenesis in back-arc basins.     

国内外铜矿勘查的现状及进展

介绍了国内外铜矿勘查的最新进展,对国内外一些典型铜矿床的地质特征进行了概括性描述；对国内外铜矿勘查途径和方法的最新进展进行了总结。这对开拓铜矿找矿思路,具有一定的现实意义。     

基于等损伤的主余震序列型地震动PGA放大系数谱研究

大地震发生后往往会伴随强余震发生,强烈余震会加重结构的破坏程度,在抗震设计及结构损伤评估中考虑余震的影响是一重要课题。采用NGA-West2数据库建立主余震序列型地震动记录数据集,基于损伤等效思想定义主余震作用下PGA放大系数α,针对单自由度体系结构,通过动力时程分析建立不同相对强度、不同场地条件下平均PGA放大系数谱,进一步通过回归分析构建PGA放大系数谱的预测方程,分析统计结果的离散性。结果表明：PGA放大系数谱受场地条件影响较小,受主余震相对强度影响显著;放大系数谱值随周期增大而减小。谱预测方程能够提供目标损伤下结构的主震PGA放大需求,并可以作为设计谱调整系数使用,以实现在结构抗震设计及结构损伤评估中考虑余震的影响。     

辽宁省海城地震前震震源错动方式的一个特点

海城地震前震的错动方式都一致,这一特点表现为各台记到的P波S波垂直向最大振幅的比值均稳定.与中国境内发生的五个震群资料对比表明,上述特点有助于区分震群和前震.     

高分一号影像数据城市生态用地监测

针对我国城市化进程不断加快,城市生态用地发生翻天覆地变化的状况下,如何及时准确地获取城市生态用地覆盖信息的问题,该文以北京部分城区高分一号遥感影像数据作为实验数据,提出一种面向对象的城市生态用地信息提取方法。通过分析城市生态用地5种地物类型的光谱信息和几何信息,建立相应的规则集以提取小尺寸遥感影像中生态用地信息;针对建筑物和裸土难以区分的问题,引入纹理信息来提高提取精度,并将含有纹理信息的规则集应用于北京市遥感影像。实验结果表明,该方法提取精度可以满足大面积的城市生态用地信息提取的需求。     

青海都兰察汗乌苏地区银、铅等多金属矿找矿前景分析

都兰县察汗乌苏地区位于柴达木盆地东南缘,地处东昆仑多金属成矿带中东部.区内地质构造复杂,岩浆活动频繁,变质作用强烈,区域Pb、Ag化探异常分布集中,铁、铜、铅、锌矿产分布密集,特别是鄂拉山组陆相火山岩系是青海省唯一发现含独立银矿的地层,因此评价研究本区出现的高、大、全Ag、Pb异常特征及其成矿规律,对本区寻找接触交代型银多金属矿具有十分重要的意义.