华北活动地块区南缘阜南-霍邱地区地壳活动习性初探     

姚大全  刘加灿 《中国地震》2005,21(2):216-223

阜南-霍邱地区地处华北和华南活动地块区边缘构造带，通过对其进行地震地质调查和综合分析研究，发现晚更新世以来该区存在强度较弱的构造变形现象，即：小震沿着主要断裂呈线性条带状分布；研究区南部及断裂近侧的上更新统中发育共轭剪节理；1970年代，研究区固始、霍邱和阜南等地陆续发生过长度不一、宽窄不等、方向不同的地裂缝，展布与肥中断裂或王老人集断裂近乎一致。本文认为，研究区局部小震丛集、上更新统中赋存共轭剪节理、裂面充填物显微揉皱变形和现代地裂缝的生成等现象，反映出地壳能量被缓慢释放和相应断裂发生微弱活动；研究区曾发生过一次破坏性地震(江口集Ms43/4地震)。综上所述，研究区地壳晚第四纪以来具有微弱活动性，且主要表现为蠕滑活动方式。  相似文献   

A geomatics data integration technique for coastal change monitoring     

J. P. Mills  S. J. Buckley  H. L. Mitchell  P. J. Clarke  S. J. Edwards 《地球表面变化过程与地形》2005,30(6):651-664

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Saprolite Remnants as Indicators of Pre-Glacial Landform Genesis in Southeast Sweden   总被引：3，自引：0，他引：3  

Mats Olvmo  Karna Lidmar-Bergström  Kerstin Ericson  Johan M. Bonow 《Geografiska Annaler: Series A, Physical Geography》2005,87(3):447-460

Twenty‐six sites with remnants of gravelly saprolites (grus) have been located in southeast Sweden. Joint block hills (castle kopjes) and steep rock walls with weathered joints as well as rounded boulders are documented to have an origin in deep weathering and subsequent stripping of saprolites. The saprolite remnants and landforms result from the fragmentation of the re‐exposed sub‐Cambrian peneplain along fracture systems. Only shallow saprolites occur on the elevated intact parts of the sub‐Cambrian peneplain, while saprolites up to 20 m thick are encountered in areas where the sub‐Cambrian peneplain is fractured and dissected. Neogene uplift with reactivation of the weathering system is thought to be the main cause of saprolite formation. Deep weathering is thus judged to have been the major agent of landform formation in the study area, while glacial and glaciofluvial erosion has contributed mainly by stripping saprolites, detaching corestones, and plucking joint blocks along weathered joints.  相似文献   

Analysis of earth dams affected by the 2001 Bhuj Earthquake   总被引：3，自引：0，他引：3  

Raghvendra Singh  Debasis Roy  Sudhir K. Jain   《Engineering Geology》2005,80(3-4):282-291

An earthquake of magnitude of 7.6 (M_w 7.6) occurred in Bhuj, India on January 26, 2001. This event inflicted damages of varying extents to a large number of small to moderate size multi-zone earth dams in the vicinity of the epicenter. Some of the distress was due to the liquefaction of saturated alluvium in foundation. Liquefaction was relatively localized for the majority of these dams because the earthquake struck in the middle of a prolonged dry season when the reservoirs behind these dams were nearly empty and shallow alluvium soils underneath the downstream portions of the dams were partly dry. Otherwise, liquefaction of foundation soils would have been more extensive and damage to these dams more significant. Six such dams have been examined in this paper. Four of these facilities, Chang, Shivlakha, Suvi, and Tapar were within the 50 km of epicenter region. These dams underwent free-field ground motion with peak ground accelerations between 0.28g to 0.52g. Of these Chang Dam underwent severe slumping, whereas Shivlakha, Suvi, and Tapar Dams were affected severely especially over the upstream sections. Fatehgadh Dam and Kaswati Dam were affected relatively less severely. Foundation conditions underneath these dams were first examined for assessing liquefaction potential. A limited amount of subsurface information available from investigations undertaken prior to the earthquake indicates that, although the foundation soils within the top 2.0 to 2.5 m underneath these dams were susceptible to liquefaction, Bhuj Earthquake did not trigger liquefaction because of lack of saturation of these layers underneath the downstream portions of these dams. These dams were then analyzed using a simple sliding block procedure using appropriate estimates of undrained soil strength parameters. The results of this analysis for these structures were found to be in general agreement with the observed deformation patterns.  相似文献   

Geochemistry and Crustal Evolution of Volcano-sedimentary Successions and Orthogneisses in the São Gabriel Block, Southernmost Brazil — Relics of Neoproterozoic Magmatic Arcs     

K. Saalmann  M.V.D. Remus  L.A. Hartmann 《Gondwana Research》2005,8(2):143-161

Precambrian metaplutonic rocks of the São Gabriel block in southernmost Brazil comprise juvenile Neoproterozoic calc-alkaline gneisses (Cambaí Complex). The connection with associated (ultra-)mafic metavolcanic and metasedimentary rocks (Palma Group) is not well established. The whole complex was deformed during the Brasiliano orogenic cycle. Both metasedimentary and metavolcanic rocks as well as metaplutonic rocks of the Cambaí Complex have been sampled for geochemical analyses in order to get constraints on the tectonic setting of these rocks and to establish a tectonic model for the São Gabriel block and its role during the assembly of West-Gondwana. The major element compositions of the igneous rocks (Palma Group and Cambaí Complex) indicate a subalkaline character; most orthogneisses have a calc-alkaline chemistry; many metavolcanic rocks of the Palma Group show signatures of low-K tholeiitic volcanic arc basalts. Trace element data, especially Ti, Zr, Y, Nb, of most igneous samples from both the lower Palma Group and the Cambaí Complex indicate origin at plate margins, i.e., in a subduction zone environment. This is corroborated by relative enrichment in LREE, low contents of Nb and other high field strength elements and enrichment in LILE like Rb, Ba, and Th. The data indicate the possible existence of two suites, an oceanic island arc and a continental arc or active continental margin. However, some ultramafic samples of the lower Palma Group in the western São Gabriel block indicate the existence of another volcanic suite with intra-plate character which possibly represents relics of oceanic island basalts (OIB). Trace element data indicate contributions from andesitic to mixed felsic and basic arc sources for the metasedimentary rocks. The patterns of chondrite- and N-MORB-normalized spider diagrams resemble the patterns of the igneous rocks, i.e., LILE and LREE enrichment and HFS depletion. The geochemical signatures of most igneous and metasedimentary samples and their low (⁸⁷Sr/⁸⁶Sr)_t ratios suggest only minor contribution of old continental crust.A geotectonic model for the São Gabriel block comprises east-ward subduction and following accretion of an intra-oceanic island arc to the eastern border of the Rio de la Plata Craton at ca. 880 Ma, and westward subduction beneath the newly formed active continental margin between ca. 750 and 700 Ma. The São Gabriel block represents relics of an early Brasiliano oceanic basin between the Rio de la Plata and Kalahari Cratons. This ocean to the east of the Rio de la Plata Craton might be traced to the north and could possibly be linked with Neoproterozoic juvenile oceanic crust in the western Brasília belt (Goiás magmatic arc).  相似文献   

Variations in elastic thickness and flexure of the Maracaibo block     

《Journal of South American Earth Sciences》2014

We estimate the lateral variations of the elastic thickness of the Maracaibo block with a 3D numerical approach by using centered finite differences. The calculation is based on solving the fourth-order partial differential equation that governs the bending of a thin plate fixed on its boundaries (zero displacement) with variable thickness (or elastic thickness for this particular case). An initial plate-load model is built and is iteratively modified to fit the general basement configuration and gravity data. The final result is an elastic thickness map that covers the Maracaibo block and the surrounding sections of the South American plate. It shows that the elastic thickness ranges from 30 km to 18 km with a mean value of 23.6 km and a mode of 26 km. The largest elastic thickness values are associated with the location of the Santa Marta Mountains and the Barinas Apure Basin, while the smallest ones with the Mérida Andes-Maracaibo Basin flexural system. The current basement configuration within the Maracaibo basin, formed as a result of its geodynamic evolution, has affected the mechanical properties of the Maracaibo block near the current Mérida Andes position. The load of the Perijá Range is compensated by a complex stress tensor, and that of the Santa Marta Mountains does not have an isostatic root as it is held by a relatively strong lithosphere.  相似文献   

Calibration of paired watersheds: Utility of moving sums in presence of externalities          下载免费PDF全文

Herbert Ssegane  Devendra M. Amatya  Augustine Muwamba  George M. Chescheir  Tim Appelboom  E.W. Tollner  Jami E. Nettles  Mohamed A. Youssef  François Birgand  R.W. Skaggs 《水文研究》2017,31(20):3458-3471

Historically, paired watershed studies have been used to quantify the hydrological effects of land use and management practices by concurrently monitoring 2 similar watersheds during calibration (pretreatment) and post‐treatment periods. This study characterizes seasonal water table and flow response to rainfall during the calibration period and tests a change detection technique of moving sums of recursive residuals (MOSUM) to select calibration periods for each control–treatment watershed pair when the regression coefficients for daily water table elevation were most stable to minimize regression model uncertainty. The control and treatment watersheds were 1 watershed of 3–4‐year‐old intensely managed loblolly pine (Pinus taeda L.) with natural understory, 1 watershed of 3–4‐year‐old loblolly pine intercropped with switchgrass (Panicum virgatum), 1 watershed of 14–15‐year‐old thinned loblolly pine with natural understory (control), and 1 watershed of switchgrass only. The study period spanned from 2009 to 2012. Silvicultural operational practices during this period acted as external factors, potentially shifting hydrologic calibration relationships between control and treatment watersheds. MOSUM results indicated significant changes in regression parameters due to silvicultural operations and were used to identify stable relationships for water table elevation. None of the calibration relationships developed using this method were significantly different from the classical calibration relationship based on published historical data. We attribute that to the similarity of historical and 2010–2012 leaf area index on control and treatment watersheds as moderated by the emergent vegetation. Although the MOSUM approach does not eliminate the need for true calibration data or replace the classic paired watershed approach, our results show that it may be an effective alternative approach when true data are unavailable, as it minimizes the impacts of external disturbances other than the treatment of interest.  相似文献   

New P–T constraints on the Tamayen glaucophane‐bearing rocks,eastern Taiwan: Perple_X modelling results and geodynamic implications          下载免费PDF全文

I. Baziotis  C.‐H. Tsai  W. G. Ernst  B.‐M. Jahn  Y. Iizuka 《Journal of Metamorphic Geology》2017,35(1):35-54

New pseudosection modelling was applied to better constrain the P–T conditions and evolution of glaucophane‐bearing rocks in the Tamayen block of the Yuli belt, recognized as the world's youngest known blueschist complex. Based on the predominant clinoamphibole, textural relationships, and mineral compositions, these glaucophane‐bearing high‐P rocks can be divided into four types. We focused on the three containing garnet. The chief phase assemblages are (in decreasing mode): amphibole + quartz + epidote + garnet + chlorite + rutile/titanite (Type‐I), phengite + amphibole + quartz + garnet + chlorite + epidote + titanite + biotite + magnetite (Type‐II), and amphibole + quartz + albite + epidote + garnet + rutile + hematite + titanite (Type‐III). Amphibole exhibits compositional zoning from core to rim as follows: glaucophane → pargasitic amphibole → actinolite (Type‐I), barroisite → Mg‐katophorite/taramite → Fe‐glaucophane (Type‐II), glaucophane → winchite (Type‐III). Using petrographic data, mineral compositions and Perple_X modelling (pseudosections and superimposed isopleths), peak P–T conditions were determined as 13 ± 1 kbar and 550 ± 40 °C for Type‐I, 10.5 ± 0.5 kbar and 560 ± 30 °C for Type‐II (thermal peak) and 11 ± 1 kbar and 530 ± 30 °C for Type‐III. The calculations yield higher pressures and temperatures than previously thought; the difference is ~1–6 kbar and 50–200 °C. The three rock types record similar P–T retrograde paths with clockwise trajectories; all rocks followed trajectories with substantial pressure decrease under near‐isothermal conditions (Type‐I and Type‐III), with the probable exception of Type‐II where decompression followed colder geotherms. The P–T paths suggest a tectonic environment in which the rocks were exhumed from maximum depths of ~45 km within a subduction channel along a relative cold geothermal gradient of ~11–14 °C km^?1.  相似文献   

基于光谱角匹配算法的水体信息提取研究     

齐庆超  张小磊  金江峰  金玉玲 《测绘与空间地理信息》2016,(2):93-96

针对水体信息提取时,传统算法不能较好地解决山体阴影被误提为水体的问题,引入多用于高光谱数据处理的光谱角匹配算法,以Land-sat8 OLI(band1-band7)为数据源,以黄河小浪底水库周边区域为实验区,开展水体信息提取研究,结果显示:水体指数法和波段关系提取的结果中有大量的山体阴影信息,提取精度不超过30%,而光谱角匹配法提取结果受阴影的影响较小,提取精度在99%以上。  相似文献   

基于线要素动态化简的匹配算法比较与评价     

陈竞男  钱海忠  王骁  何海威  胡慧明 《测绘科学技术学报》2016,(1)

矢量线要素数据来源多样,细节层次不一,限制了已有匹配算法正确率的提高,同时也给算法评价带来困难。化简可以减少线要素细节层次,提取其主要形态,据此提出一种基于线要素动态化简的匹配算法评价新方法。对不同匹配算法采用相同数据,在相同化简算法支撑下进行匹配,从而实现对不同匹配算法的评价。首先,阐述动态化简方法提取线要素主要形态的过程;其次,利用动态化简分别辅助4种已有匹配算法,获取每个匹配算法的最优匹配正确率;最后,将4种匹配算法的原始匹配结果与加入动态化简后的匹配结果进行对比,分析化简对匹配结果的影响,并把该影响运用到匹配算法的比较和评价中来。其中,1通过匹配正确率变化、误匹配等分析了匹配算法的数据适用性;2通过化简比例系数K变化时新增匹配数量的统计,评价了匹配算法对线要素局部细节的敏感程度并提出该指标的量化方法;3结合匹配算法采用的匹配相似度指标对其作出评价。  相似文献