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排序方式： 共有195条查询结果，搜索用时 31 毫秒
91.
A. İdil Çakıroğlu Ü. Nihan Tavşanoğlu Eti E. Levi Thomas A. Davidson Tuba Bucak Arda Özen Gürçay K. Akyıldız Erik Jeppesen Meryem Beklioğlu 《Journal of Paleolimnology》2014,52(4):367-383
Cladocerans are valuable indicators of environmental change in lakes. Their fossils provide information on past changes in lake environments. However, few studies have quantitatively examined the relationships between contemporary and sub-fossil cladoceran assemblages and no investigations are available from Mediterranean lakes where salinity, eutrophication and top-down control of large-bodied cladocerans are known to be important. Here we compared contemporary Cladocera assemblages, sampled in summer, from both littoral and pelagic zones, with their sub-fossil remains from surface sediment samples from 40 Turkish, mainly shallow, lakes. A total of 20 and 27 taxa were recorded in the contemporary and surface sediment samples, respectively. Procrustes rotation was applied to both the principal components analysis (PCA) and redundancy analysis (RDA) ordinations in order to explore the relationship between the cladoceran community and the environmental variables. Procrustes rotation analysis based on PCA showed a significant accord between both littoral and combined pelagic–littoral contemporary and sedimentary assemblages. RDA ordinations indicated that a similar proportion of variance was explained by environmental variation for the contemporary and fossil Cladocera data. Total phosphorus and salinity were significant explanatory variables for the contemporary assemblage, whereas salinity emerged as the only significant variable for the sedimentary assemblage. The residuals from the Procrustes rotation identified a number of lakes with a high degree of dissimilarity between modern and sub-fossil assemblages. Analysis showed that high salinity, deep water and high macrophyte abundance were linked to a lower accord between contemporary and sedimentary assemblages. This low accord was, generally the result of poor representation of some salinity tolerant, pelagic and macrophyte-associated taxa in the contemporary samples. This study provides further confirmation that there is a robust relationship between samples of modern cladoceran assemblages and their sedimentary remains. Thus, sub-fossil cladoceran assemblages from sediment cores can be used with confidence to track long-term changes in this environmentally sensitive group and in Mediterranean lakes, subjected to large inter-annual variation in water level, salinity and nutrients. 相似文献
92.
The recently compiled Turkish strong motion database: preliminary investigation for seismological parameters 总被引：5，自引：0，他引：5
Sinan Akkar Zehra Çağnan Emrah Yenier Özgür Erdoğan M. Abdullah Sandıkkaya Polat Gülkan 《Journal of Seismology》2010,14(3):457-479
Strong motion data recorded by the Turkish national strong motion network has been compiled and processed systematically for
the first time, together with detailed geophysical and geotechnical site measurements for all of its stations. The catalog
information of 18 seismological agencies and other sources were examined to obtain reliable source, geometry, and distance
parameters for each event. The high quality digital and analog strong motion data was processed by a uniform methodology to
remove the high- and low-frequency noise. Currently, the seismological and spectral information of 4,607 strong motion records
are available for use by earth scientists and earthquake engineers. In this article, we present the fundamental features of
this database and explain our methodology in their calculation. We present several comparisons of our database with other
related studies to verify our approach during the computational stage of the seismological parameters. The results confirm
the reliability of our calculations. The database has also enabled us to derive empirical magnitude conversion relationships
to estimate moment magnitude in terms of different magnitude scales. The article ends with a discussion of the likely improvements
in the European accelerometric data through contributions from this strong motion database applicable for seismically active
shallow-crust regions. The findings of this article emphasize the necessity of global strong motion databases in Europe for
better estimation of seismic hazard in regions of similar seismotectonic environment. 相似文献
93.
94.
叶面积指数（LAI）是生态环境研究中一个关键的生物物理变量,是陆地植被能量交换的重要途径。基于多角度高光谱植被辐射传输理论,根据DART模型,将天顶角和方位角离散成61个方向组合,建立适于多角度高光谱遥感数据的叶面积指数反演查找表;选取长白山地区高光谱多角度PROBA/CHRIS遥感数据,在进行HRIS数据预处理的基础上,利用最小二乘原理进行CHRIS数据与LAI查找表匹配,反演研究区的LAI;并对490 nm和700 nm波长在不同LAI和61个离散方向的BRDF敏感性因子进行评价分析：随着LAI值的增大,490 nm波长的BRDF值先增大后减小, 700 nm波长的BRDF值减小;BRDF值沿天顶角增大的方向下降,在天顶附近时值为最小。 相似文献
95.
M. Keskin A. V. Chugaev V. A. Lebedev E. V. Sharkov V. Oyan O. Kavak 《Journal of Volcanology and Seismology》2012,6(6):361-382
A geochemical and isotope-geochemical (Sr-Nd-Pb) study has been carried out for the Karacada? neovolcanic area, which is situated within the frontal part of the Arabian plate. The obtained data and the results of petrological modeling show that the petrogenesis of parental magmas in the Karacada? neovolcanic area involved two compositionally different mantle sources; one consisted of garnet-bearing peridotites of the asthenosphere mantle and the other was spinel-bearing peridotites of the enriched subcontinental lithosphere mantle. During early stages in the evolution of the magmatic system, deep-seated asthenospheric magmas were ascending to the surface while intensively interacting with the melts that had been generated at upper mantle depths. The interaction gradually diminished, so that the later effusive rocks mostly have compositions that are similar to those of the primitive asthenospheric magmas. It is shown that a significant (up to 17–18 wt % of the mantle melt) assimilation of crustal material could take place only during the initial phases of the magmatism. Periodic replenishment of the magma chambers by primitive magmas, which resulted in an observable high degree of homogeneity in the composition of young effusive rocks, was also of importance in the petrogenesis of lavas during the evolution of volcanic activity. 相似文献
96.
通过岩心的详细观察,结合测井、录井资料综合分析,在环县地区上三叠统延长组长63砂层组中,识别出了三角洲前缘、前三角洲和深湖3种亚相,和水下分流河道、支流间湾、河口砂坝、远砂坝、前三角洲泥、砂质碎屑流沉积、浊流沉积、液化流沉积、滑塌沉积和深湖泥10种微相。编绘了一系列沉积微相连井剖面图和长63砂层组的沉积微相平面展布图,表明研究区西部、北部及东北部发育三角洲前缘亚相,研究区中部和东南部发育深湖亚相。在深湖亚相中除了深湖泥外,发育大量的砂质碎屑流和浊流等重力流沉积。作者首次提出了源于浅水区的砂级沉积物是通过前三角洲上的一系列水道搬运至深湖区形成重力流沉积的。综合以上研究成果,建立起了该区的沉积模式。论文最后分析了研究区的油气潜力,指出水下分流河道和砂质碎屑流沉积两种微相的储集性能最好。由于本区砂体横向尖灭现象普遍,可形成一些规模较大的岩性圈闭,是岩性油气藏勘探的有利目标区。 相似文献
97.
98.
İrem Elitez Cenk Yaltırak Akın Kürçer Ersin Özdemir Çağıl Uygun Güldoğan 《Geodinamica Acta》2017,29(1):91-102
The Kibyra Fault is considered as the most significant evidence about the existence of the NE–SW-striking left-lateral Burdur-Fethiye Fault Zone in the south-western Anatolia in previous studies. However, recent studies show that there is a shear regime, named the Burdur-Fethiye Shear Zone, dominated by normal and left-lateral oblique normal faults in this region. A large number of ancient cities lie on this zone and many of them have been damaged by ancient earthquakes. One of these ancient cities is the ancient city of Kibyra. Most of previous studies suggest the Kibyra Fault depending on the damage in the city. However, the closest fault is located on the western side of the city and the earthquake damage was most likely caused by ground shaking. In this study, the existence of the supposed Kibyra Fault is discussed by integrating field studies, geological maps, trench data, digital elevation model and geomorphological analysis. In conclusion, it is understood that there is no evidence directly indicating a 35-km-long left-lateral fault in this region. The aim of this study is to examine the existence of the Kibyra Fault, take a different approach to the active fault studies and emphasise the importance of active faults for socio-economic conditions. 相似文献
99.
巢湖平顶山北坡剖面早三叠世碳、氧同位素地层学研究 总被引：8，自引：1，他引：7
取自安徽巢湖平顶山北坡下三叠统剖面中 12 4个碳、氧同位素样品的分析结果表明 ,由 Induan阶→Olenekian阶下部→ Olenekian阶中部 ,δ1 3C平均值由 - 1.8‰减小到 - 3.9‰后又快速增大到 3.7‰ ,δ1 8O的平均值由 - 6 .9‰降低到 - 8.6‰后又回升到 - 6 .5‰。 Induan阶的中、上部δ1 3C呈缓慢上升趋势 ,Olenekian阶下部δ1 3C呈明显的“U”型谷 ,Olenekian阶中部 δ1 3C表现为显著正漂。碳、氧同位素演化特征表明 ,早三叠世 Induan期环境恶劣、生物复苏缓慢 ,Olenekian早期的地质事件导致生物再次绝灭 ,延缓了生物复苏的进程。 相似文献
100.