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991.
Mustafa Aktar Hayrullah Karabulut Serdar Özalaybey Dean Childs 《Geophysical Journal International》2007,171(3):1363-1375
Three main shocks M-1, M-2 and M-3 (17 October 2005 at 05:45 UTC, M w 5.4; 17 October at 09:46 UTC, M w 5.8 and 20 October at 21:40 UTC, M w 5.9) and their associated aftershocks within the Gulf of S i ğac i k, 50 km southwest of Izmir, Turkey were studied in detail. A temporary seismic network deployed during the activity allowed the hypocentre of M-3 and subsequent aftershocks to be determined with high accuracy. A relative relocation technique was used to improve the epicentres of M-1 and M-2. All three main shocks have strike-slip mechanisms which agree with the linear trends of the aftershock locations. Two distinct zones were illuminated by the aftershock locations. The zones contain clear echelon patterns with slightly different orientations from the trend of the aftershock distribution. M-2 and M-3 ruptured along of the eastern rupture zone which aligns N45°E. However the strike direction of M-1 is not clearly identified. The alignment of the two rupture zones intersect at their southern terminus at an angle of 90°. The fault zones form conjugate pair system and static triggering is considered as a probable mechanism for the sequential west to east occurrence of M-1, M-2 and M-3. This earthquake sequence provides seismological evidence for conjugate strike-slip faulting co-existing within a region dominated by north–south extension and well-developed east–west trending normal faults. 相似文献
992.
The Otranto–Leuca coastal tract is marked by the presence of numerous sea caves placed close to present sea level. They are located generally at the back of a shore platform covered by a sequence of breccia deposits, marine sediments and speleothems. At Grotta di Masseria dell'Orte, marine cemented sands rest on a narrow shore platform at about 6.2 m above mean sea level and are covered by speleothems older than 185 ka. At Grotta del Diavolo, which is mostly filled by breccia deposits, three beach levels have been detected at about 3.0, 3.5 and 5.9 m above msl. They are either covered by or overlie speleothems that yield an U/Th age of 340, 78 ka and between 170.3 and 146.5, respectively. Geomorphological evidence and radiometric ages indicate that the area after a period of uplift has been tectonically stable since the last part of the Middle Pleistocene so that marine landforms close to the present shoreline underwent a polycyclic evolution. The sedimentary fills of sea caves formed during Middle-Late Pleistocene glacial stages, when arid or semiarid conditions promoted the removal of regolith and the development of thick breccia deposits. During Marine Isotope Stages (MIS) 9.3, 5.5 and 5.1, cave sediments were partially eroded whereas beach layers and related speleothems developed. These are, in fact, the only marine isotope stages marked by a sea level position which in this Mediterranean region was either close to, or slightly higher than, the present one. 相似文献
993.
994.
地球科学涉及的研究对象和问题通常以长时间、大尺度、大规模为特征。这些研究不仅需要在实验室中进行,而且更需要大范围、长时间系列的实地观测资料。用于观测、实验、分析与计算的设施和仪器对地球科学领域的研究十分重要。GEO地球科学设施计划(1999—2003)是GEO历史上首次提出的“设施计划”,它从地球环境观测系统、计算系统、实验室系统及样本与资料存贮系统4个方面对NSF已拥有和拟发展的设施作了阐述。通过对GEO在1999年前已拥有、计划1999—2003年使用及目前的实行情况3方面对NSF用于地球环境观测系统的设施作较为全面的介绍。 相似文献
995.
中更新世气候转型期是第四纪古气候研究的一个特殊时期。利用大洋钻探ODP 184航次在南海北部钻取的1144站时间分辨率高达约290年的沉积物样品,开展中更新世气候转型期古气候变化的研究。在中更新世距今80~100万年前,浮游和底栖有孔虫壳体的稳定氧碳同位素变化揭示出,中更新世气候转型中心,即中更新世革命0.9 Ma左右,南海北部表层海水温度的降低和降水量的增加指示东亚冬、夏季风增强。以中更新世革命为界,水体垂向结构上温跃层和营养跃层的深度从之前的间冰期较浅转变为之后的间冰期较深,底层水与表层水的垂直温度梯度从冰期时较大转变为冰期时较小。轨道尺度上,冰消期时南海北部的表层水、次表层水和底层水的变化几乎是同时发生的,不存在超前或滞后的相位差。千年尺度上,有孔虫的氧碳同位素变化都呈现出非常明显的约0.8 ka和约1.4 ka的气候波动周期。氧同位素0.8 ka滤波显示出:在中更新世气候转型期,较强的信号主要出现在间冰期,有时也出现在冰期,与晚第四纪千年尺度气候波动主要出现在冰期不同,说明中更新世的气候转型不仅表现在轨道尺度的气候周期变化上,同时也体现在千年尺度气候波动的特征变化中。
相似文献
996.
陆源碎屑与碳酸盐混合沉积研究中的几点思考 总被引:11,自引:0,他引:11
在前人研究的基础上,结合一些具体研究实例,对混合沉积的定义进行了修正和补充;对混积岩和混积层系重新进行分类和命名;根据混合沉积的定义、成因、成分、结构、沉积构造及接触关系等因素,按照“沉积事件+剖面结构”的原则,提出了渐变式、突变式和复合式3种成因类型,对前人的研究成果进行了概括和归纳;对混合沉积的控制因素进行了深入讨论;在以碳酸盐沉积为主和以陆源碎屑沉积为主的2类沉积背景下详细论述了层序格架中混合沉积的发育情况;结合混合沉积本身的特点讨论了混合沉积与油气的关系。最后针对混合沉积研究现状,指出了该领域研究中存在的问题,并对未来的研究方向进行了展望。 相似文献
997.
阿尔金断裂花海段新生代变形特征及时间 总被引:6,自引:0,他引:6
在地表地质调查并结合钻井资料分析的基础上,主要通过地震剖面的精细地质解释,对阿尔金断裂东段的构造变形特征进行了系统分析。认为阿尔金断裂经阿克塞至肃北向北东东方向延伸,既没有止于玉门市西北的宽台山,也没有延伸至金塔盆地,而是止于其间的花海盆地花探7井东侧。阿尔金断裂花海段的变形时间主要为渐新世晚期、上新世末期和晚更新世末,以后者最为强烈。与红柳峡段的对比说明变形强度自西向东逐渐减弱,变形方式主要为走滑兼逆冲,主要构造样式为半花状构造,并派生有一系列向南西西方向收敛的弧形断裂。 相似文献
998.
Spatial pattern of Karst rock desertification in the Middle of Guizhou Province,Southwestern China 总被引:13,自引:0,他引:13
Karst rocky desertification is a typical type of land degradation in the Southwestern China. It has great ecological and economical
implications for the local people. Landsat images from the middle of Guizhou Province collected in 1974, 1993 and 2001 were
used for change detection of the pattern of Karst rocky desertification. The results show the following findings: (1) Desertification
area expanded drastically in 27 years, at an increasing rate about 116.2 km2/year. (2) High areas (900–1,500 m) are the most affected. (3) Areas with the slope <5° or >25° are also easily tend to be
Karst rocky deserted. (4) The process of Karst rocky desertification is nearly irreversible. Few areas of Karst rocky desertification
could be meliorated to non-desertification land. (5) Most of the degraded lands are located in the south and the central of
the study region, and the meliorated land areas are sparsely located in the east and the west part of the region. All these
findings would provide bases for the decision-making of the local government to improve the Karst rocky desertification 相似文献
999.
1000.
Coastal processes and environmental hazards: the Buenos Aires (Argentina) and Venetian (Italy) littorals 总被引:1,自引:0,他引:1
Jorge Pousa Luigi Tosi Eduardo Kruse Dardo Guaraglia Maurizio Bonardi Andrea Mazzoldi Federica Rizzetto Enrique Schnack 《Environmental Geology》2007,51(8):1307-1316
The Buenos Aires (Argentina) and Venice (Italy) coastlands have experienced significant saltwater contamination of the phreatic
aquifer, coastal erosion, hydrodynamic changes and relative sea level rise processes due to natural and man-induced factors.
These factors expose coastal areas to morpho-hydro-geological hazards, such as soil desertification, frequency and degree
of flooding, littoral erosion, and the silting of river mouths and channels. Man-made interventions and actions, such as beach
mining, construction of coastal structures and exploitation of aquifers without an adequate knowledge of the hydrology setting
and an adequate management program, worsen these natural hazards. Uncontrolled human activity induces environmental damage
to the overall coastal plains. The coastal plains play an important role in the social/economic development of the two regions
based on land use, such as agriculture, horticulture, breeding, and tourism, as well as industry. Results of investigations
on saltwater contamination, sea level rise and morphological changes recently performed in these two coastal areas are presented
here. 相似文献