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101.
Although there has been significant progress in the seismic imaging of mantle heterogeneity,the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models.To address this question,we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns.A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow,without imposing prescribed surface velocities(i.e.,plate-like boundary condition).As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip(rigid) boundary condition.A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved,and its geographical location is fixed during the evolution of mantle flow.Considering the impact of different assumed surface boundary conditions(rigid and plate-like) on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure.Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term,stable pattern of thermal heterogeneity in the lowermost mantle that resembles the presentday Large Low Shear Velocity Provinces(LLSVPs),especially below the Pacific.The evolution of subduction zones may be,however,influenced by the mantle-wide flow driven by deeply-rooted and longlived superplumes since Archean times.These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique slow feature distinct from the two principal LLSVPs.We find there is no need for dense chemical ’piles’ in the lower mantle to generate a stable distribution of temperature anomalies that are correlated to the LLSVPs and the Perm Anomaly.Our tomography-based convection simulations also demonstrate that intraplate volcanism in the south-east Pacific may be interpreted in terms of shallow small-scale convection triggered by a superplume beneath the East Pacific Rise. 相似文献
102.
基于ICESat/GLAS高度计数据的SRTM数据精度评估——以青藏高原地区为例 总被引:1,自引:0,他引:1
为全面了解航天飞机雷达测图计划(shuttle Radar topography mission,SRTM)高程数据的精度及误差特征,利用精度更高的ICESat/GLAS激光高度计数据(简称ICESat高度计数据)为参照数据,以具有多种地貌类型的中国青藏高原地区为实验区,采用双线性插值算法分析了SRTM在中国青藏高原地区的高程精度,以及SRTM高程数据与地形因子(坡度和坡向)间的关系。实验结果表明:在青藏高原地区,ICESat高度计数据与相对应的SRTM高程数据高度相关,相关系数高达0.999 8;SRTM的系统误差为2.36±16.48 m,中误差(RMSE)为16.65 m;当坡度低于25°时,SRTM高程数据精度随坡度增大而显著降低。此外,相对于ICESat高度计数据,SRTM在青藏高原地区N,NW和NE方向的测量值偏高,在S,SE和SW方向的测量值偏低。 相似文献
103.
Interplay between an axial channel belt,slope gullies and overbank deposition in the Puchkirchen Formation in the Molasse Basin,Austria 下载免费PDF全文
Larisa U. Masalimova Donald R. Lowe Timothy Mchargue Richard Derksen 《Sedimentology》2015,62(6):1717-1748
Deep‐water sediments in the Molasse Basin, Austria, were deposited in a narrow foreland basin dominated by a large channel belt located between the steep Alpine fold and thrust belt to the south and the gentler northern slope off the Bohemian Massif. Several gas fields occur outside the channel belt, along the outer bend of a large meander. Accumulation of these overbank sediments reflects a complicated interplay between slope accommodation and debris‐flow and turbidity‐flow interaction within the channel. The tectonically oversteepened northern slope of the basin (ca 2 to 3°) developed a regionally important erosional surface, the Northern Slope Unconformity, which can be traced seismically for >100 km in an east–west direction and >20 km from the channel to the north. The slope preserves numerous gullies sourced from the north that eroded into the channel belt. These gullies were ca 20 km long, <1 km wide and ca 200 m deep. As the channel aggraded, largely inactive and empty gullies served as entry points into the overbank area for turbidity currents within the axial channel. Subsequently, debris‐flow mounds, 7 km wide and >15 km long, plugged and forced the main channel to step abruptly ca 7 km to the south. This resulted in development of an abrupt turn in the channel pathway that propagated to the east and probably played a role in forming a sinuous channel later. As debris‐flow topography was healed, flows spread out onto narrow area between the main channel and northern slope forming a broad fine‐grained apron that serves as the main gas reservoir in this area. This model of the overbank splay formation and the resulting stratigraphic architecture within the confined basin could be applied in modern and ancient systems or for subsurface hydrocarbon reservoirs where three‐dimensional seismic‐reflection data is limited. This study elucidates the geomorphology of the oversteepened slope of the under‐riding plate and its effects on the sedimentation. 相似文献
104.
通过对济南2013年12月—2018年2月PM2.5质量浓度数据分析得出,PM2.5质量浓度平均和最大值均为冬季最高,春秋季次之,夏季最低;PM2.5质量浓度值1月和12月最高,8月最低;其质量浓度呈明显的逐年递减趋势。在不同风向上PM2.5质量浓度存在显著差异性,在N风向和ESE(盛行)风向上均出现了质量浓度较大值,一方面与污染物的异地输送有关,另一方面与济南的特殊地形有关。研究表明,无论污染源在山脉的背风侧还是迎风侧,都很容易导致高浓度污染;尤其在冬季,山脉地形还会加重逆温影响,使污染程度加重。通过相关性研究发现,冬季、春季和秋季,PM2.5质量浓度与相对湿度和平均总云量均呈正相关,与日照时数及其距平呈负相关;冬季,PM2.5质量浓度与平均气温及其距平以及最高、最低气温均呈正相关,与平均、最高、最低气压均呈负相关;春季和秋季,PM2.5质量浓度与气温距平值呈正相关;夏季和秋季,PM2.5质量浓度与日降水量呈负相关,而且随着雨强的增大,对PM2.5的洗消作用越显著。上述变量间相关性均通过了P≤0.01显著性检验。 相似文献
105.
In this paper,a hindcast study of the record-breaking rainfall event occurring in Beijing on 21July 2012,is conducted by using the Weather Research and Forecasting(WRF)model forced by National Centers for Environmental Prediction(NCEP)Global Forecasting System(GFS)outputs,paired with an investigation of the impact of topography in this region.The results indicate that WRF can reasonably predict the salient features of orographic precipitation;the 24-h rainfall amount and spatial distribution compare reasonably well with the observations.The hindcast simulation also indicates that rainfall events can be predicted approximately 36 h ahead.When the topography is removed,the spatial distribution of rainfall changes remarkably,suggesting the importance of the topography in determining rainfall structure.These results also indicate that prediction of such city-scale heavy rainfall events would benefit from a high-resolution prediction system. 相似文献
106.
对1950-2010年影响浙西南的热带气旋降水的移动路径、影响时间、强度、西风槽、西南季风以及地形等主要因子进行分析.结果表明:在玉环南-厦门一带登陆的热带气旋是影响浙西南的热带气旋中正面影响浙西南的类型,影响时间和最大平均过程降雨量、最大过程雨量存在着正相关关系,热带气旋的强度与其降水强度相关性较高.西风槽的存在不仅影响着热带气旋路径的变化,其槽前的西南气流也为热带气旋降水提供充足的水汽,同时槽后冷空气与热带气旋相结合,使丽水的西北部出现另一个强降水中心.西南季风为登陆后的热带气旋提供了水汽条件,使降水得到增幅.浙西南独特的地形,使在厦门以北到玉环以南登陆后西进、西北行或西北行后在120°E以西转向北上的热带气旋迎着山脉进入,降水强度明显加强. 相似文献
107.
108.
109.
月球Airy均衡状态与月壳厚度估计 总被引:2,自引:0,他引:2
月球水准面异常和表面地形变化是其内部密度不均匀和各个界面的起伏变化的体现,因此利用水准面和地形之比(geoid to topography ratio,GTR)可估计月球均衡和月壳厚度。本文基于月球重力场模型SGM100h和地形模型STM359_grid-02,经过去除表面玄武岩填充和深层异常质量影响,并结合理论Airy均衡模型中GTR与参考月壳厚度的关系,计算得到了新的月壳厚度模型。该模型的月壳平均厚度为36.9 km,背面比正面平均厚约13.5 km,Apollo12/14登陆点的月壳厚度分别是28.3 km和29.1 km。在各月海盆地存在着中央较薄、四周逐渐增厚的趋势。 相似文献
110.