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1.
Derived gravity field of the seismogenic upper crust of SE Germany and West Bohemia and its comparison with seismicity 总被引：2，自引：2，他引：0
The gravity field of the seismogenic upper crust was derived from the Bouguer gravity map by applying the Butterworth high-pass
filter in the wave-number domain. The cutoff wavelength of the filter was 110 km, to pass the gravity signals of structures
within the 18 km thick seismogenic layer. The derived residual gravity map reveals potential stress concentrating structures,
which may cause seismicity provided they lie within the existing zones of weakness. Furthermore we derived a shaded relief
map of the horizontal gravity gradient, which highlighted the tectonic lines accompanied by density contrast. The directional
analysis of this map shows three dominant strike directions. The most prominent one is “the Hercynian” NW-SE strike direction
represented by the Franconian Line, the Gera-Jáchymov Fault Zone and the Elbe Zone. The second dominant strike is the Rhenisch
NNE-SSW trending represented by the Upper Rhine Graben Zone, Rheinsberg-Heldburg Line and several Proterozoic volcanic belts
in the Teplá-Barrandien Unit. The third pronounced trending of the ENE-WSW direction is represented by the Erzgebirge and
Eger Graben gravity low. The N-S trending Rostock-Leipzig-Regensburg Zone (Pritzwalk-Naab Lineament) is not distinctly reflected
in the derived gravity maps, although many fault segments have a meridian direction.
The relative reactivation potential of some pre-existing fault systems identified in the gravity map was studied with respect
to the wide range of the recent stress configuration determined in the West Bohemia/Vogtland region. The resulting diagrams
show that the steep NNW-SSE to N-S faults (represented by some segments of the Mariánské Lázně Fault Zone) are oriented favourably
for reactivation. On the contrary, the orientation of the ENE-WSW faults limiting the Eger Graben (Litoměřice Fault, etc.)
is unfavourable for reactivation for all dip values. 相似文献
2.
Study on coupling between deep and shallow structures of Xingtai area and some significant questions
IntroductionIn order to gain a clear idea of the deep tectonic environment of Xingtai earthquake area,three wide-angle deep seismic renectionlrefraction profiles have been conducted through the are4they are Yuanshi--Ji'nan profile, Renxian--Wuqing profile and Tat' an--LongyaM inzhou profi I e.The Yuanshi--Ji'nan profile passes through the epicenter of the Ms=7.2 main shock andTat' ~ongyaO--X inzhou profi ie passes through the ep icenter of the Ms=6. 8 earthquake. Duringthe "Eighth Five-… 相似文献
3.
The Chirripó hydrological research site (CHRS) is located within the Chirripó National Park, Costa Rica (between 3100 and 3820 m asl) whereby ~100 km2 are covered by Páramo, a high-elevation tropical grassland ecosystem. A lake district with approximately 30 lakes of glacial origin is also protected in this area. The CHRS has been monitored since April 2015 with the aim of establishing the first water isotope baseline for the Central American Páramo. At a regional scale, the water isotope ratios (δ2H and δ18O) in precipitation and surface water at CHRS are useful for describing the governing moisture transport from the Caribbean Sea and Pacific Ocean and the complex rainfall producing systems across the N–S mountain range of Central America. These data are also providing unique information about the evaporation and water balance conditions of tropical glacial lakes and the formation of orographic and convective precipitation in high-elevation tropical ecosystems. Current data sets from CHRS include continuous lake water temperature and meteorological conditions (i.e., precipitation amount, air temperature and relative humidity), as well as water stable isotopes in precipitation, stream water, and lake water (daily to biweekly sampling frequency). Stream water is collected at several locations across the topographic gradient whereas lake water is sampled in the three main lake systems of CHRS. CHRS serves as a reference site for conducting pilot isotopic research in high-elevation ecosystems to advance the atmospheric, hydrogeological and ecohydrological studies in these understudied biomes. All data from April 2015 to November 2020 are publicly available. 相似文献
4.
The Yuguang basin is a half-graben basin in the basin-range tectonic zone in northwest Beijing, located at the northern end of the Shanxi graben system, and the Yuguang basin southern marginal fault (YBSMF) controls the formation of this basin. A linear fault escarpment has formed in the proluvial fan on the piedmont fault zone of the Tangshankou segment of YBSMF. A trench across this escarpment reveals three paleo-earthquake events on two active faults. One fault ruptured at about 9ka for the first time, and then faulted again at about 7.3ka, causing the formation and synchronous activity of another fault. Finally, they faulted for the third time, but we cannot determine the faulting time due to the lack of relevant surface deposition. The accumulative vertical displacement of these three events is about 8.1m. We estimate that the average recurrence period of the piedmont fault is about 1.7ka, and the average slip rate of the piedmont fault is about 1.6mm/a. We also estimate the reference magnitude of each event according to the empirical formula. 相似文献
5.
以沂沭断裂带南段(沂水县—郯城县)及周边地区为研究对象,收集该地区的遥感影像、数字高程模型和布格重力数据,研究区域构造地貌和地壳深部构造特征,进一步对沂沭断裂带南段与周边断裂的交切关系予以分析.研究结果显示:在遥感影像中,蒙山山前断裂和苍尼断裂的构造地貌特征明显,断裂沿线发育水系转弯、河流错断、断层陡坎、断层崖、断层三角面等地貌现象,反映了两断裂正断兼左旋走滑的活动性质,其中蒙山山前断裂向东延伸至莒南县附近,苍尼断裂向东延至郯城一带,两条断裂在地貌上均截切了沂沭断裂带;在重力细节场中,两断裂形成了不同尺度上的重力梯度带,切割至下地壳深度,在地壳浅层至深层均交切于沂沭断裂带,且交切处出现扭曲、断折、串珠状等重力异常现象,证实其在地壳深部切穿沂沭断裂带.因此,两条断裂的遥感和重力场解译结果具有明显的一致性,在地貌及深部均截切沂沭断裂带南段,使其出现分段性特征.此外,在临沭县附近发现了一条新断裂,即相庄—沙岭断裂,该断裂在地貌上呈北高南低,沿线水系发生左旋同步转弯,且在1—3阶重力细节场中形成线性梯度条带,故推测该断裂下切至中地壳深度,在临沭县附近截切沂沭断裂带交切于东地堑,并未延伸至西地堑. 相似文献
6.
Evidence of fluid interaction with normal faults comes from their varied role as flow barriers or conduits in hydrocarbon basins and as hosting structures for hydrothermal mineralisation, and from fault-rock assemblages in exhumed footwalls of steep active normal faults and metamorphic core complexes. These last suggest involvement of predominantly aqueous fluids over a broad depth range, with implications for fault shear resistance and the mechanics of normal fault reactivation. A general downwards progression in fault rock assemblages (high-level breccia-gouge (often clay-rich) → cataclasites → phyllonites → mylonite → mylonitic gneiss with the onset of greenschist phyllonites occurring near the base of the seismogenic crust) is inferred for normal fault zones developed in quartzo-feldspathic continental crust. Fluid inclusion studies in hydrothermal veining from some footwall assemblages suggest a transition from hydrostatic to suprahydrostatic fluid pressures over the depth range 3–5 km, with some evidence for near-lithostatic to hydrostatic pressure cycling towards the base of the seismogenic zone in the phyllonitic assemblages. Development of fault-fracture meshes through mixed-mode brittle failure in rock-masses with strong competence layering is promoted by low effective stress in the absence of thoroughgoing cohesionless faults that are favourably oriented for reactivation. Meshes may develop around normal faults in the near-surface under hydrostatic fluid pressures to depths determined by rock tensile strength, and at greater depths in overpressured portions of normal fault zones and at stress heterogeneities, especially dilational jogs. Overpressures localised within developing normal fault zones also determine the extent to which they may reutilise existing discontinuities (for example, low-angle thrust faults). Brittle failure mode plots demonstrate that reactivation of existing low-angle faults under vertical σ1 trajectories is only likely if fluid overpressures are localised within the fault zone and the surrounding rock retains significant tensile strength. Migrating pore fluids interact both statically and dynamically with normal faults. Static effects include consideration of the relative permeability of the faults with respect to the country rock, and juxtaposition effects which determine whether a fault is transmissive to flow or acts as an impermeable barrier. Strong directional permeability is expected in the subhorizontal σ2 direction parallel to intersections between minor faults, extension fractures, and stylolites. Three dynamic mechanisms tied to the seismic stress cycle may contribute to fluid redistribution: (i) cycling of mean stress coupled to shear stress, sometimes leading to postfailure expulsion of fluid from vertical fractures; (ii) suction pump action at dilational fault jogs; and, (iii) fault-valve action when a normal fault transects a seal capping either uniformly overpressured crust or overpressures localised to the immediate vicinity of the fault zone at depth. The combination of σ2 directional permeability with fluid redistribution from mean stress cycling may lead to hydraulic communication along strike, contributing to the protracted earthquake sequences that characterise normal fault systems. 相似文献
7.
In order to explain the presence of voluminous volcanic debris avalanche deposits around a stratovolcano, reactivation of vertical faults beneath a volcanic cone has been tested using analogue models. Reactivation of a single vertical fault beneath a cone generates a normal fault and an upturning of the layers creating a bulge on the flank. The upturning induces a flank collapse characterized by a typical horseshoe-shaped scar called an avalanche caldera. Reactivation of two vertical faults beneath a cone also generates a normal fault and a summit bulge. This bulge may result from the movement along a reverse fault. A large collapse is generated within the angle created by the two vertical faults. The angle of the collapse can be up to 140° whereas this angle is typically 120° for a dome intrusion. Collapse is instantaneous and is favoured by the presence of ductile layers (ash-and-pumice formations in the example considered) in a stratovolcano complex. The model may be applicable to volcanoes in a state of dormancy (or extinction) in regions with active regional tectonism. We suggest this mechanism of collapse in the case of the Cantal stratovolcano (Massif Central, France) to explain the presence of voluminous volcanic debris avalanche deposits around this volcano. 相似文献
8.
通过跨银川断陷盆地,完成了一条长68.9 km的高分辨深地震反射探测剖面,首次获得了银川盆地地壳精细结构、地堑型断陷盆地深部断裂系（黄河断裂、银川断裂、贺兰山东麓断裂）特征及深浅构造关系.结果表明：银川断陷盆地上地壳为双程走时8 s（深度约20 km）反射面以上的区域,上地壳上部地层层位丰富,地层分段连续性较好,上地壳下部地层分层特征不明显,地质构造简单;下地壳(8～13 s)反射能量较弱,反射同相轴不明显;下地壳下部壳幔过渡带（13 s附近）由一组能量较强、持续时间较长（1.5 s）的反射波组组成,厚度约4.5 km.芦花台断裂、银川断裂分别于12～12.5 km、18～19 km深处交汇于贺兰山东麓断裂,贺兰山东麓断裂于28～29 km深处交汇于黄河断裂,黄河断裂为错断Moho面的深大断裂,银川地堑为以黄河断裂为主,其他断裂为辅组合而成的负花状构造.根据贺兰山东麓断裂和银川断裂的相互关系,认为贺兰山东麓断裂对1739年平罗—银川8级地震起主要控制作用. 相似文献
9.
拉分盆地是走滑断层系中受拉伸作用形成的断陷盆地.一般在两条平行断层控制下发育.盆地形似菱形,几何形态主要受两条主控走滑断层错距和叠接长度影响.本文以青藏高原东北缘海原断裂带老龙湾拉分盆地第四纪所处的构造环境为基础,参考盆地周围断层几何分布,建立了三维有限元数值模型,模拟该拉分盆地的演化过程;进一步分析了断层力学性质、地壳分层结构等各因素对盆地形成和演化的影响.模拟结果显示,盆地地表沉降伴随有下地壳物质的上涌,此上涌对盆地地表沉降存在阻碍作用.各因素的影响具体表现为:(1)断层力学性质(弹性模量和黏滞系数)越弱,其对构造应力较低的传递效率导致盆地两端差异性运动越明显,从而形成较大的盆地地表沉降和明显的上地壳减薄.(2)平行主控断层的叠接长度反映盆地形成的拉伸作用范围,叠接长度越大,相同的差异性运动在单位面积形成的拉伸应力越小,盆地地表沉降较小.(3)下地壳流变性影响其物质的上涌量,下地壳黏滞系数越小,其对上部拉伸作用的响应越明显,上涌量越大,此上涌对上地壳沉降形成的阻碍作用也越明显.根据老龙湾拉分盆地所处的构造格局,将平行断层的叠接长度取20km,当断层黏滞系数取值为周围基岩的1/10,参考该盆地第四纪构造演化历史,模拟得到的盆地第四纪下沉量与盆地内第四系沉积层厚度在规模上近似,下地壳黏滞系数取值在(2.5~5.0)×1021 Pa·s范围内时,盆地下沉量模拟结果与老龙湾拉分盆地第四系地层厚度吻合较好. 相似文献
10.
以华北地块作为实施“国际地壳与上地幔模型计划（IGCP-474）”示范区,我们综合京津唐及邻区的8条宽角反射地震剖面地壳速度结构, 计算了该区域不同构造域上、中及下地壳平均速度和厚度.利用格里金插值技术构建上、中、下地壳平均速度、厚度和底界深度在空间上变化图像.这些图像指示出,京津唐及邻区发育沿近东西和北东两个方向展布的隆起与拗陷,发育受北东向断裂控制的断隆和断坳.这些地质构造的形成与该区域发生在中生代以来的构造运动密切相关,推断京津唐及邻区在中新生代至少发生三期较强烈的构造运动.结合区域构造研究成果得出,近东西向展布的隆起和拗陷形成于三叠纪,北东向展布的隆起和拗陷形成于侏罗纪,受北东向断裂控制的断隆和断坳则形成于白垩纪以来.由于中地壳为壳内低速层,与上、下地壳的变形规律截然不同,以塑性变形为主,造成中地壳在隆起部位厚度大、速度低,拗陷部位厚度小、速度高,其厚度较大的部位地壳强度整体降低,在后期构造运动中易发生断裂变形,进而控制京津唐及邻区现今地震活动. 相似文献
11.
Control of paths of quaternary volcanic products in western Bohemian Massif by rejuvenated Variscan triple junction of ancient microplates 总被引：1，自引：1，他引：0
Our objective is to look for deep paths of Cenozoic volcanism and migration routes of active mantle volatiles through the
lithosphere of the western Bohemian Massif. We show that the rejuvenated junction of three mantle domains, delimited by different
orientation of seismic anisotropy and belonging to originally separated microplates — the Saxothuringian (ST), Moldanubian
(MD) and Teplá-Barrandian (TB) — can provide the easiest upward routes of fluids through the deep lithosphere. Geographic
distribution of mantle-fluid escapes at the surface suggests fluid migration through the ductile lower crust and through partly
open faults in the rigid upper crust, which is locally detached and shifted from its lower part and from the mantle lithosphere.
Present-day escapes of mantle-derived helium and CO2 concentrate mainly in two tectonically different crust edifices — in the Cheb Basin (CHB) and in an allochtonous block called
the Mariánské Lázně Complex (MLC). Crystalline basement of the CHB developed above the Variscan ‘triple junction’ of the mantle
lithosphere domains. The basement was extended during the Cenozoic and dissected by systems of faults into small partly sunken
blocks. Thanks to buoyancy the mantle fluids migrate upwards along the lithosphere junction into the faulted basement of the
CHB. The highest CO2 flow and the highest 3He/4He ratios are observed at intersections of major normal faults and along the southern boundary of the Smrčiny (Fichtelgebirge)
granite Pluton. The fluid escapes are separated from the earthquake swarm epicentres. Routes of the fluids to the MLC are
longer and more complicated. Surface escapes tap the mantle fluids mainly from the Mariánské Lázně Fault (MLF) and from the
tectonic boundaries along which the MLC block of the TB lower crust was thrust over the ST complexes. Hypocentres of earthquake
swarms of the two major focal areas at Novy Kostel and Lazy, located mainly at depths of 6–13 km, reside either in granite
or in underlying gneiss, while the escapes of mantle fluids follow major faults or boundaries of crystalline units outside
the Smrčiny and Karlovy Vary granite Plutons. We suggest that primarily those parts of faults in the upper crust, which is
strengthened by granite magmatism and rigid enough to selectively accumulate stresses, are seismoactive. On the other hand,
other parts of the faults tapping ascending mantle volatiles are ‘lubricated’ by the fluids and secondary mineralogical changes,
and thus they cannot accumulate sufficient stresses to be released by earthquakes. A comparison of the most probable paths
of the mantle fluids with the space-time distribution of the Novy Kostel hypocentres does not seem to support the model of
the earthquake swarms triggered by pressurized fluids of mantle origin. 相似文献
12.
The use of mass balances in the investigation of the biogeochemical cycle of sulfur is reviewed for three systems: 1) upland catchments, 2) wetlands, and 3) lakes. In upland catchments, the major inputs of sulfur are via wet and dry atmospheric deposition, whereas outputs or losses occur primarily through volatilization and/or runoff. In addition, sulfur may be stored in vegetation and in the forest floor. In wetlands (particularly peatlands), a large proportion of the sulfur inputs are derived from surface and groundwater originating in the upland system. Because of the fluctuating water table in wetlands, they can act as a source or sink for sulfate, depending on the redox conditions. Wetlands, therefore, can significantly affect input-output budgets for lakes. In most lakes, only a small portion of the sulfate input is retained, (i.e. not lost from the lake via outflow), indicating that there is an excess of sulfate relative to biological needs. Seepage lakes are exceptions to this generalization. Although the reactivity of the sulfate input to many lakes is low, sulfate levels, especially in regions receiving substantial atmospheric sulfur deposition, are high enough that the portion reduced results in substantial in-lake alkalinity production; in fact, in many cases, alkalinity production from sulfate reduction is greater than that resulting from not only other in-lake processes but from external sources (the catchment) as well. The importance of mass balance investigations in elucidating the biogeochemical cycling of sulfur is stressed and the need for additional studies on a whole-system basis stressed. © 1997 John Wiley & Sons, Ltd. 相似文献
13.
The three-dimensional arrangement of volcanic deposits in strike-slip basins is not only the product of volcanic processes,
but also of tectonic processes. We use a strike-slip basin within the Jurassic arc of southern Arizona (Santa Rita Glance
Conglomerate) to construct a facies model for a strike-slip basin dominated by volcanism. This model is applicable to releasing-bend
strike-slip basins, bounded on one side by a curved and dipping strike-slip fault, and on the other by curved normal faults.
Numerous, very deep unconformities are formed during localized uplift in the basin as it passes through smaller restraining
bends along the strike-slip fault. In our facies model, the basin fill thins and volcanism decreases markedly away from the
master strike-slip fault (“deep” end), where subsidence is greatest, toward the basin-bounding normal faults (“shallow” end).
Talus cone-alluvial fan deposits are largely restricted to the master fault-proximal (deep) end of the basin. Volcanic centers
are sited along the master fault and along splays of it within the master fault-proximal (deep) end of the basin. To a lesser
degree, volcanic centers also form along the curved faults that form structural highs between sub-basins and those that bound
the distal ends of the basin. Abundant volcanism along the master fault and its splays kept the deep (master fault-proximal)
end of the basin overfilled, so that it could not provide accommodation for reworked tuffs and extrabasinally-sourced ignimbrites
that dominate the shallow (underfilled) end of the basin. This pattern of basin fill contrasts markedly with that of nonvolcanic
strike-slip basins on transform margins, where clastic sedimentation commonly cannot keep pace with subsidence in the master
fault-proximal end. Volcanic and subvolcanic rocks in the strike-slip basin largely record polygenetic (explosive and effusive)
small-volume eruptions from many vents in the complexly faulted basin, referred to here as multi-vent complexes. Multi-vent
complexes like these reflect proximity to a continuously active fault zone, where numerous strands of the fault frequently
plumb small batches of magma to the surface. Releasing-bend extension promotes small, multivent styles of volcanism in preference
to caldera collapse, which is more likely to form at releasing step-overs along a strike-slip fault.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
14.
M. J. Branney 《Bulletin of Volcanology》1995,57(5):303-318
Structures at calderas may form as a result of precursory tumescence, subsidence due withdrawal of magmatic support, resurgence, and regional tectonism. Structural reactivation and overprinting are common. To explore which types of structures may derive directly from subsidence without other factors, evidence is reviewed from pits caused by the melting of buried ice blocks, mining subsidence, scaled subsidence models, and from over 50 calderas. This review suggests that complex patterns of peripheral deformation, with multiple ring and arcuate fractures both inside and outside caldera rims, topographic embayments, arcuate graben, and concentric zones of extension and compression may form as a direct result of subsidence and do not require a complex subsidence and inflation history. Downsag is a feature of many calderas and it does not indicate subsidence on an inward-dipping ring fault, as has been inferred previously. Where magmatic inflation is absent or slight, initial arcuate faults formed during collapse are likely to be multiple, and dip outwards to vertical. Associated downsag causes the peripheries of calderas undergo radial (centripetal) extension, and this accounts for some of the complex peripheral fractures, arcuate crevasses, graben, and some topographic moats. The structural boundary of a caldera, defined here as the outermost limits of subsidence and related deformation including downsag, commonly lies outside ring faults and outside the embayed topographic wall. It is likely to be funnel-shaped, i.e. inward-dipping, even though ring and arcuate fractures within it may dip outward. Inward-dipping arcuate normal faults at shallow levels and steep inward-dipping contacts between a caldera's fill and walls may both occur at a caldera that has initially subsided on outward-dipping ring faults. They arise due to peripheral surficial extension, gravitational spreading and scarp collapse. Topographic enlargement at some calderas and the formation of embayments may reflect general progressive downsag and localized downsag, respectively. These processes may occur in addition to surficial degradation of oversteep ring-fault scarps. 相似文献
15.
Eoghan P. Holohan Benjamin van Wyk de Vries Valentin R. Troll 《Bulletin of Volcanology》2008,70(7):773-796
Regional-scale faulting, particularly in strike-slip tectonic regimes, is a relatively poorly constrained factor in the formation
of caldera volcanoes. To examine interactions between structures associated with regional-tectonic strike-slip deformation
and volcano-tectonic caldera subsidence, we made scaled analogue models. Tabular (sill-like) inclusions of creamed honey in
a sand/gypsum mix replicated shallow-level granitic magma chambers in the brittle upper crust. Lateral motion of a base plate
sited below half the sand/gypsum pack allowed simulation of regional strike-slip deformation. Our experiments modelled: (1)
strike-slip deformation of a homogeneous brittle medium; (2) strike-slip deformation of a brittle medium containing a passive
magma reservoir; (3) caldera collapse into sill-like magma reservoirs without regional strike-slip deformation; and (4) caldera
collapse into sill-like magma reservoirs after regional strike-slip deformation. Our results show that whilst the magma chamber
shape principally influences the development and geometry of volcano-tectonic collapse structures, regional-tectonic strike-slip
faults (Riedel shears and Y-shears) may affect a caldera’s structural evolution in two main ways. Firstly, regional strike-slip
faults above the magma chamber may form a pre-collapse structural grain that is exploited and reactivated during subsidence.
Our experiments show that such faults may preferentially reactivate where tangential to the collapse area and coincident with
the chamber margins. In this case, volcano-tectonic extension in the caldera periphery tends to localise on regional-tectonic
faults that lie just outside the chamber margins. In addition, volcano-tectonic reverse faults may link with and reactivate
pre-collapse regional-tectonic faults that lie just inside the chamber margins. Secondly, where regional-tectonic strike-slip
faults define corners in the magma chamber margin, they may halt the propagation of volcano-tectonic reverse faults. The experiments
also highlight the potential difficulties in assessing the relative contributions of volcano-tectonic and regional-tectonic
subsidence processes to the final caldera structure seen in the field. Disruption of the pre-collapse surface by regional-tectonic
faulting was preserved during coherent volcano-tectonic subsidence to produce a caldera floor of differentially-subsided fault
blocks. Without definitive evidence for syn-eruptive growth faulting, thickness changes in caldera fill across such regional-tectonic
fault blocks in nature could be mistaken as evidence for piecemeal volcano-tectonic collapse. 相似文献
16.
地震事件中,断层破裂面的倾角大小直接影响到地表强地震动的分布状态,尤其在断陷盆地中,强地面运动特征还可能受到盆地结构及盆地内多条围限断层的影响.本文模拟了银川断陷盆地内的活动断层--银川隐伏断层南段发生Mw6.5特征地震时,断层破裂面倾角在30°~85°范围内变化时引起的强地面运动,探讨了断层破裂面倾角变化对盆地内强地面运动分布特征和强度的影响.结果表明:破裂面倾角较缓时,银川盆地内的强地面运动分布区域不仅仅决定于发震断层的产状,同时还受到断层上盘距离最近的芦花台断层的影响,致使强地面运动集中于两条断层所围限的区域;随着发震断层破裂面的倾角逐渐增大,强地面运动以发震断层产状的影响为主,强震集中区向发震断层靠近并分布于发震断层上盘,且沿断层走向方向出现了强度不同的地震动反射区;尤其是发震断层破裂面倾角接近垂直时,受银川盆地"西陡东缓"结构和盆地西边界贺兰山东麓断裂反射作用的影响,竖向地震动反射区强度在远离发震断层的西北方向明显增大,致使芦花台断层附近区域与银川断层南段上盘区域成为地震发生时可能遭受震害最严重的地区.本文探讨结果提醒我们在类似区域的活动断层附近进行建(构)筑规划和地震工程设计时,有必要考虑发震断层破裂面倾角大小和盆地内其它断层构造的共同影响,综合评价潜在地震对盆地内近断层地表及各类建(构)筑物的危害性. 相似文献
17.
The thickness of the mechanical layer that hosts a group of faults can be estimated from the spacing of saturated faults (i.e. the constant spacing between faults when the fault system is fully developed and has attained its final fault density). We measured fault spacing for a group of saturated active normal faults on Miyako‐jima Island (southern Ryukyu Arc, Japan) and estimated the thickness of the faulted mechanical layer. The measured fault spacing is 1.30 ±0.14 km, and the thickness of the mechanical layer is < 3 km, which is the upper limit of the seismogenic zone. This faulted mechanical layer corresponds to a sedimentary layer in which earthquakes cannot occur. Results indicate that the shallow (< 3 km depth) normal faults on Miyako‐jima Island do not have the potential to cause medium‐size earthquakes as individual faults. The origin of the shallow normal faults might be related to the presence of a larger‐scale, deeper fault. The results indicate that fault spacing provides important information on the potential magnitude of earthquakes associated with active faults. 相似文献
18.
We test the applicability of quartz optically stimulated luminescence (OSL) dating on clastic lake sediments to investigate whether this dating method can be applied to study the timing and rate of deposition in Holocene fluvio-deltaic lakes. Our study concerns the filling of a lake by the Angstel-Vecht system, part of the Rhine delta in the western Netherlands. Age constraints are provided by radiocarbon dates on the development and abandonment of the fluvial channels debouching into the lake. Results indicate that light exposure prior to deposition and burial was sufficient to reset the OSL signal of the vast majority of the quartz grains. Special attention was given to accurate estimation of the dose rate in the laminated and bedded deposits. The OSL ages obtained are in good agreement with the age constraints, especially for the relatively coarse sediments. OSL results indicate that the filling of the lake took about 700 years, with a sedimentation rate of ～3 mm per year. This study is a demonstration of the use of OSL dating of sand-sized quartz to determine the timing and rate of sedimentation in a Holocene fluvio-deltaic environment. 相似文献
19.
河西走廊花海古湖泊全新世白云石的发现及其环境意义 总被引：4，自引：3，他引：1
通过对河西走廊花海古湖泊沉积物的X衍射分析发现,全新世期间有明显的白云石沉积.岩性、沉积过程、石膏以及Fe3+含量的变化表明,花海湖全新世白云石沉积环境以还原环境为主,即还原环境利于白云石的形成,为白云石的成因研究提供了新的证据.白云石作为碳酸盐矿物,可以反映湖水盐度,但并非直接指示了湖水的咸化.随着湖水盐度的进一步增加,在硫酸盐型湖泊中,白云石含量随盐度的增加而相应减少,表明利用白云石分析湖水盐度时需要结合其他矿物进行分析.结合石膏含量的变化,花海湖全新世时期白云石含量的变化可以揭示该区域湖水盐度的变化.在10.478.87 cal ka B.P.早全新世时期,湖水的盐度较高,气候由干向湿转变;8.87 cal ka B.P.时期,有大量石膏沉积,显示了湖水盐度的进一步升高,气候干旱;随后湖水相对淡化,气候湿润;5.50 cal ka B.P.至今,沉积出现间断,气候逐渐干旱. 相似文献
20.
《Limnologica》2017
Temperate and tropical shallow lakes differ in several fundamental aspects with respect to management of eutrophication. High altitude tropical shallow lakes are a special case, showing similarities with temperate and tropical lakes. We studied the ecology of the eutrophic high-altitude tropical lake Yahuarcocha in the Ecuadorian Andes and evaluated the potential of biomanipulation to control eutrophication. With a toxin-producing Cylindrospermopsis bloom, low Secchi depth and low submerged macrophyte cover, Yahuarcocha is clearly in a turbid ecosystem state. Relatively low nutrient concentrations should theoretically allow for a shift to a clear water state through biomanipulation. Top-down control of phytoplankton by zooplankton, however, is complicated by the (1) absence of predatory fish, (2) fish community dominated by small poecelid species, (3) lack of a refuge for zooplankton from fish predation within the macrophytes, and (4) persistent, grazing resistant bloom of the cyanobacterium Cylindrospermopsis. In these aspects, lake Yahuarcocha is more similar to tropical shallow lakes, probably because water temperature is high relative to the mean air temperature and because of the absence of a cold season. The fish and macrophyte communities consisted almost entirely of exotic species. The exotic fish species probably stabilized the turbid state in the lake. 相似文献