Seismic and field evidence for selective inversion of Cretaceous normal faults, Salta rift, northwest Argentina   总被引：1，自引：0，他引：1  

Jonas Kley  Eduardo A. Rossello  Csar R. Monaldi  Bjrn Habighorst 《Tectonophysics》2005,399(1-4):155

Northwestern Argentina was the site of the continental Salta rift in Cretaceous to Paleogene time. The Salta rift had a complex geometry with several subbasins of different trends and subsidence patterns surrounding a central high. Fault trends in the rift were extremely variable. There is evidence of normal and/or transfer faults trending N, NE, E and SE. It is not clear if all these faults were active at the same time, indicating a poorly defined extension direction, or if they formed in different, non-coaxial extension phases. In either case, their trends were very likely influenced by preexisting fault systems. Beginning in early Eocene time, the rift basins were superseded by Andean foreland basins and later became caught in the Andean thrust deformation propagating eastward, resulting in the inversion of rift faults. Due to their different orientations, not all faults were equally prone to reactivation as thrusts. N to NNE trending faults were apparently most strongly inverted, probably often to a degree where the traces of their normal fault origin have become obliterated. We present seismic evidence of moderately inverted N trending faults in the Tres Cruces basin and field examples of preserved E trending normal faults. However, reactivation sometimes also affects faults trending approximately parallel to the main Neogene shortening direction, indicating short-term deviations from the general pattern of Neogene thrust deformation. These pulses of orogen-parallel contraction may be linked to the intermittent activity of oblique transfer zones.  相似文献   

Review of paleoseismological and active fault studies in Taiwan in the light of the Chichi earthquake of September 21, 1999   总被引：1，自引：0，他引：1  

Yoko Ota  Yue-Gau Chen  Wen-Shan Chen 《Tectonophysics》2005,408(1-4):63

This paper reviews the research on active and earthquake faults in Taiwan conducted prior and after the 1999 Chichi earthquake. The Chichi earthquake plays as a turning point of the relevant studies, since the 1999 coseismic surface rupture exactly follows preexisting fault scarps, created in turn by previous seismic events along the Chelungpu Fault. This fact indicates that the precise mapping on the other active faults is fundamental to predict the location of surface rupture caused by large future earthquakes. Since 1999, many trenching studies have been carried out along the Chichi earthquake fault. A few of them demonstrates that the penultimate event is as young as probably only 200–430 years old; however, some others show a rather old age of several hundreds years or even older for the last faulting event before 1999. More trenching studies are necessary for such a long fault in order to understand the possible segmentation features and the correlation of the paleoseismic events identified along the entire fault length. In addition, we further discuss the offshore faulting associated with seismic event along the eastern coast of Taiwan, where the multiple Holocene terraces are well known.  相似文献   

广东省沿海经济带区域差异探析     

刘志霞  张加恭 《云南地理环境研究》2006,18(6):57-62

广东省沿海经济带的发展对整个广东省的经济有极大的影响。目前，其整体水平高于国内其他省份的沿海经济带，但是其内部区域差异较大。主要表现在经济总量、经济发展水平、产业结构等单要素方面。采用聚类分析法划分了广东省沿海经济带的结构层次，并分析不同层次的特点。进而揭示了广东省沿海经济带巨大的区域差异给整个区域发展所带来的问题。最后，在分析区域差异及其负面影响的基础上，提出广东沿海经济带协调发展的几点对策。  相似文献   

Transboundary biodiversity conservation of the Pha Taem Protected Forest Complex: A bioregional approach     

Yongyut Trisurat   《Applied geography (Sevenoaks, England)》2006,26(3-4):260-275

With the financial assistance from the International Tropical Timber Organization (ITTO), the Thailand's Royal Forest Department (RFD) has initiated a strategy for cooperation in transboundary biodiversity conservation with Cambodia and Laos. The Pha Taem Protected Forest Complex (PPFC) in northeastern region was chosen as a pilot project because of the increasing pressure on biodiversity from illegal trade in plants and wildlife across the tri-national borders. The PPFC covers five protected areas in Thailand and adjoins the Phouxeingthong National Biodiversity Conservation Area (NCBA) in Laos and the Cambodia's Protected Forest for Conservation of Genetic Resources of Plants and Wildlife. Two important outputs derived from the project phase I (2001–2004) were a long-term management plan in a framework of transboundary biodiversity conservation and initiative cooperation between the three countries. Cooperation is achieved at certain level and Laos is reluctant to nominate the Phouxeingthong NBCA for inclusion in the project's second phase. In addition, forest cover in buffer zone has been encroached for agricultural practices. The ecological management zones using bioregional approach was developed to provide a framework for transboundary biodiversity conservation in the adjoining protected forests and reducing the conflict of resource uses by local residents in the buffer zone.  相似文献   

Decentralization of the Nation's Main Street: New Coastal‐Proximity‐Based Portrayals of Population Distribution in the United States, 1950–2000     

Christopher J. Henrie  David A. Plane 《The Professional geographer》2006,58(4):448-459

Almost half a century has passed since Jean Gottmann coined the term “Megalopolis” in reference to the almost continuously urbanized stretch of land spanning the East Coast of the United States from southern New Hampshire to northern Virginia. Because a disproportionate concentration of population resided in this Megalopolis, the northeastern core enjoyed an economic and cultural supremacy, and he termed the Megalopolis “The Main Street of the Nation.” By the later 1960s and 1970s, however, population migration patterns began to reflect the influence exerted by the emergence of a second national core centered on the large metropolitan areas along the Pacific Coast, especially those of the Los Angeles and Bay Area conurbations in California. Although of different character, this burgeoning concentration of population, economic activity, and cultural influence may reflect the development of a West Coast Megalopolis that could soon rival the original Megalopolis of the Northeastern Corridor. Today, the U.S. population distribution is largely a bicoastal one. This article documents the emergence of this bicoastal population distribution. Using historical census data and GIS technology, we present a number of novel ways to graphically portray and examine this population redistribution phenomenon. The United States is not unique in witnessing an increasing share of its inhabitants clustering in coastal zones. Current critical policy concerns about the worldwide vulnerability of coastal populations have focused the need for better coastal population estimates and better mapping methods for portraying population redistribution trends.  相似文献   

高边坡岩体卸荷带划分的量化研究   总被引：7，自引：0，他引：7  

郑达  黄润秋 《水文地质工程地质》2006,33(5):9-12

边坡卸荷及其卸荷带是西南地区高边坡一种常见的现象，对岩石边坡稳定性及其它岩石工程问题有重要的影响。在分析目前卸荷带划分方法的基础上，根据卸荷带的形成机理及地质表现，提出了用裂隙率、张开裂隙率和“隙宽和”3个量化指标进行卸荷带的划分。结合实际工程，进行了大量的现场裂隙测量，分析结果表明，3个量化指标对卸荷带的强弱有较好的响应关系，作为卸荷带划分的量化指标具有较好的可操作性。进一步，结合卸荷带的地质特点，提出了所研究的具体工程其卸荷带划分的建议方案。  相似文献   

Analyzing the dynamics of Dafeng coastal wetland based on remote sensing image     

Yuezhen SHI Dongjun XIN 《中国地球化学学报》2006,25(B08):213-213

Dafeng wetland is the largest coastal wetland in Asia, located on the shore of the Yellow Sea. Recently, inning, irrationality utilizing, and water contaminating all threaten it, so the area of the wetland is decreasing and its quality is declining increasingly. Therefore, it is significative to analyze the dynamics of wetland with RS image of Dafeng coastal wetland. To enhance the clustering, fuzzy c-mean algorithm is improved and used to cluster Dafeng coastal wetland. Through the improvement, the problem is solved that assortment is not very good bringing by the difference of sample number. Furthermore, changing information about Dafeng coastal wetland is analyzed by dynamic degree model and the check module of software erdas is used to analyze the dynamics of wetland. Integrating local data with improved fuzzy c-mean algorithm and dynamic degree model mentioned above, dynamics degree of Dafeng coastal wetland＇s area is calculated. The calculating result shows that the area of tour and residence increases greatly while that of bulrush and grassplot decreases largely, that of woodland changes little. The conclusion accords with the fact the main factors include natural and man-made ones, which lead to Dafeng coastal wetland resource change. From nature, coast expansion caused by bedload sediment makes wetland away from sea, disappearing finally. On the other hand, many tour projects are constructed, including training center, reception center, education center, etc; Part of the wetland is utilized as residence, pound, farm, salt field, etc. All of those account for about half of the wetland. Further, fertilizer, pesticide and machine noise contaminate the wetland environment. Finally, problem of management is one of the main restriction factors. Managing manner of traditional agriculture, growth of tourism and expansion of coast are the main driving factors for wetland changes.  相似文献   

Characteristics of natural low pH groundwater in the coastal aquifers near Beihai, China     

Xun ZHOU Rui LI Hua ZHANG Li ZHANG 《中国地球化学学报》2006,25(B08):228-228

Groundwater with low total dissolved solids （less than 200 mg/L） occurs in the unconfined and confined aquifers near Beihai in southern Guangxi, China. Under natural conditions the groundwater ranges in pH from 3,33 to 7,0 with an average value of 5.12. The pH in the unconfined aquifer varies from 3.67 to 7.0 with an average value of 5.17 and the pH in the confined aquifer is in the range 3.33-6.97 with an average value of 5.07. The pH in the groundwater does not show significantly increasing or decreasing trends with time. Fluctuations in pH exist at some of the monitoring wells and the pH in groundwater is a bit higher in the rainy season than in the dry season, Monitoring data show that the pH in rainwater is higher than in groundwater in the unconfined aquifer, whereas the pH in the latter is a bit higher than in the confined aquifer. A slightly decreasing trend in the pH was also found from the inland area to the coastal zone. The occurrence of weakly acidic groundwater in this area is attributed to the recharge from low pH precipitation and the multi-aquifer and leaky groundwater system.  相似文献   

Morphology and stratigraphy of the late Quaternary lower Brazos valley: Implications for paleo-climate, discharge and sediment delivery     

Dennis A. Sylvia  William E. Galloway   《Sedimentary Geology》2006,190(1-4):159-175

A shallow coring and geophysical logging program has recorded the sedimentary fill of the Brazos River valley in the Texas Gulf Coastal Plain. Thermoluminescence dates together with new and recalibrated published radiocarbon dates show the valley fill to include extensive, sandy, buried falling stage and lowstand Oxygen Isotope Stage (OIS) 3 and 2 deposits. These alluvial deposits are punctuated by numerous paleosoil horizons that record alternating periods of cutting, bypass and accumulation. Maximum valley incision and two periods of terrace formation preceded marine lowstand conditions, suggesting significant discordance between preserved fluvial and classical marine system tracts. The latest Pleistocene incision and fill history appears related to cycles of increased discharge and incision, followed by system equilibration and terrace formation. Analysis of the Brazos River incised valley and its contained paleochannels indicates that latest Pleistocene mean annual discharge was as much as four times greater than that of today. This magnitude of discharge in the Brazos would require a two-fold increase in precipitation across the drainage basin. Such an increase is comparable to the present day measured positive El Niño winter precipitation anomaly across the region. Paleochannel geometries and the stratigraphic and sedimentologic data from this investigation support the hypothesis that periods of high-amplitude, El Niño-like climatic perturbations characterized the late Quaternary climate of the south-central and southwestern U.S. This period of high discharge coincides, at least in part, with late OIS 3 progradation of the Brazos delta to the shelf margin, OIS 3 and 2 valley incision across the Texas shelf, and concomitant sand bypass to intraslope basins beyond the shelf edge.  相似文献   

Structure, geometry and formation of brittle discontinuities in anisotropic crystalline rocks of the Central Gotthard Massif, Switzerland     

Christian Zangerl  Simon Loew  Erik Eberhardt 《Eclogae Geologicae Helvetiae》2006,99(2):271-290

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