Geomorphic indices and relative tectonic uplift in the Guerrero sector of the Mexican forearc     

Krzysztof Gaidzik  María Teresa Ramírez-Herrera 《地学前缘(英文版)》2017,8(4):885-902

Tectonically active areas, such as forearc regions, commonly show contrasting relief, differential tectonic uplift, variations in erosion rates, in river incision, and in channel gradient produced by ongoing tectonic deformation. Thus, information on the tectonic activity of a defined area could be derived via landscape analysis. This study uses topography and geomorphic indices to extract signals of ongoing tectonic deformation along the Mexican subduction forearc within the Guerrero sector. For this purpose, we use field data, topographical data, knickpoints, the ratio of volume to area (R_VA), the stream-length gradient index (SL), and the normalized channel steepness index (k_sn).The results of the applied landscape analysis reveal considerable variations in relief, topography and geomorphic indices values along the Guerrero sector of the Mexican subduction zone. We argue that the reported differences are indicative of tectonic deformation and of variations in relative tectonic uplift along the studied forearc. A significant drop from central and eastern parts of the study area towards the west in values of R_VA (from ～500 to ～300), SL (from ～500 to ca. 400), maximum SL (from ～1500–2500 to ～1000) and k_sn (from ～150 to ～100) denotes a decrease in relative tectonic uplift in the same direction. We suggest that applied geomorphic indices values and forearc topography are independent of climate and lithology. Actual mechanisms responsible for the observed variations and inferred changes in relative forearc tectonic uplift call for further studies that explain the physical processes that control the forearc along strike uplift variations and that determine the rates of uplift. The proposed methodology and results obtained through this study could prove useful to scientists who study the geomorphology of forearc regions and active subduction zones.  相似文献   

CME和冕洞边缘结构的可能关系     

罗葆荣 《地球物理学进展》1999,14(Z1):142

本文分析了１９８０ 、１９８４ 和１９８９ 年ＳＭＭ 卫星观测到的１４０ 次日冕物质抛射（ＣＭＥ） 事件在时空分布上与“冕洞边缘结构”、耀斑爆发和爆发日珥等事件的相关关系结果表明, ＣＭＥ 事件与日冕边缘结构的关系最密切此外, ＣＭＥ与赤道冕洞具有同步的长期演化关系由此认为, 冕洞边缘结构对ＣＭＥ的可能贡献是不可忽视的  相似文献   

全新世以来山东半岛东北部海面变化的河流地貌响应   总被引：6，自引：1，他引：5  

王庆 《地理科学》1999,19(3):225-236

对全新世以来山东半岛东北部沿岸的相对海面（基准面）变化,不同河流有截然不同的地貌响应方式。大沽夹河型河流的下游河谷中有分别与相对海面升降对应的溯源堆积期和溯源侵蚀期,但不同规模的河流仍有差异。黄水河型河流河谷未因基准面升降而发生侵蚀或堆积,河谷仅起了输沙通道的作用。此外,大沽夹河型河流的中下游河型在相对海面上升或下降时,还可能发生相应地网状化或曲流化。  相似文献   

Palaeointensity results from Ethiopian basalts: implications for the Oligocene geomagnetic field strength     

Janna Riisager  Mireille Perrin  & Pierre Rochette 《Geophysical Journal International》1999,138(2):590-596

From a large collection of Ethiopian flood basalts (~30  Myr old) sampled for magnetostratigraphy, ⁴⁰Ar/³⁹Ar geochronology and geochemical investigations, 47 samples were selected in order to test their suitability for Thellier palaeointensity experiments. Only 17 samples from eight individual flows yielded reliable palaeointensity estimates, with flow-mean virtual dipole moments ranging from 3.0 to 10.5 × 10²²  A  m² .
  A critical review of the Oligocene palaeointensity data set, including these new Ethiopian data, indicates an Oligocene mean virtual dipole moment of 5.1 ± 2.5 × 10²²  A  m² for the complete data set. After applying mild selection criteria, the reduced data set yields a mean value of only 4.6 ± 1.9 × 10²²  A  m² . This value is significantly lower than the present-day field strength but is higher than the Mesozoic dipole low mean field. This low Oligocene field might be in agreement with the high palaeosecular variation and rather high non-dipole field invoked around 30  Ma. However, the Oligocene data set is largely dependent on the palaeointensity determinations from Armenia, obtained mainly from baked contacts, which show amazingly low dispersion at both flow and between-flow levels. More data are needed to reduce the weight of these determinations on the mean value and avoid a possible bias.  相似文献   

表征海相烃源岩有机质成熟度的若干重要指标的对比与研究   总被引：21，自引：1，他引：20  

涂建琪  金奎励 《地球科学进展》1999,14(1):18-23

对目前表征海相烃源岩有机质成熟度的几个重要指标（镜质体反射率,沥青反射率,镜状体反射率、动物有机碎屑反射率及牙形刺色变指数等）进行了探讨与对比,并在总结它们各自优缺点的基础上,提出了选择海相烃源岩有机质成熟度评价指标的原则,进而提出牙形刺相对荧光强度（Ｉ５４６）是表征海相烃源岩有机质成熟度的良好指标,其具有较广泛的适用性。  相似文献   

Experimental and numerical investigation for energy dissipation of supercritical flow in sudden contractions          下载免费PDF全文

Rasoul Daneshfaraz  Ehsan Aminvash  Reza Esmaeli  Sina Sadeghfam  John Abraham 《地下水科学与工程》2020,8(4):396-406

Dealing with kinetic energy is one of the most important problems in hydraulic structures, and this energy can damage downstream structures. This study aims to study energy dissipation of supercritical water flow passing through a sudden contraction. The experiments were conducted on a sudden contraction with 15 cm width. A 30 cm wide flume was installed. The relative contraction ranged from 8.9 to 9.7, where relative contraction refers to the ratio of contraction width to initial flow depth. The Froude value in the investigation varied from 2 to 7. The contraction width of numerical simulation was 5~15 cm, the relative contraction was 8.9~12.42, and the Froude value ranged from 8.9~12.42. In order to simulate turbulence, the k-ε RNG model was harnessed. The experimental and numerical results demonstrate that the energy dissipation increases with the increase of Froude value. Also, with the sudden contraction, the rate of relative depreciation of energy is increased due to the increase in backwater profile and downstream flow depth. The experimentation verifies the numerical results with a correlation coefficient of 0.99 and the root mean square error is 0.02.  相似文献   

主磁场谐波成分的空间相对强度分析     

吴迎燕  高国明  杨建元  张学民 《地震》2017,37(4):93-101

利用IGRF国际参考地磁场模型, 计算并分析了7~13阶球谐成分对主磁场的贡献。 结果表明, 地磁场要素F、 H和I的空间梯度具有显著的空间不均匀性, 有些区域梯度变化平缓, 有些地区梯度呈涡状结构, 进而由地磁场的空间梯度估算得到卫星高度的空间相对变化强度, 以及卫星上安装磁强计的伸杆震颤可能引起的观测误差。 此外, 主磁场梯度的长期变化非常缓慢, 在大约150年间其最大变化强度约为6 nT。 对于中国电磁卫星5年的设计寿命而言, 梯度变化幅度可能约为0.04 nT, 该梯度变化量对于主磁场的空间相对强度不会产生显著影响。  相似文献   

基于地磁场相对古强度变化的下蜀黄土年代序列及其古气候意义          下载免费PDF全文

任翌成  李徐生  韩志勇  陈英勇  汪雨辰  刘梦慧  潘柔娴  鹿化煜 《地球物理学报》2020,63(5):2024-2035

分布于宁镇地区的下蜀黄土年代标尺研究薄弱.我们以镇江大港钻孔岩芯的下蜀黄土为例,探讨了下蜀黄土记录地磁场相对古强度的可靠性.岩石磁学的实验显示,下蜀黄土大体上符合估计相对古强度对沉积物的要求.以低频磁化率()作为天然剩磁(NRM300)的归一化因子,我们获得了下蜀黄土记录的地磁场相对古强度变化.通过与邻区和全球的单个及合成曲线的对比,我们发现大港钻孔岩芯的相对古强度记录展现出主要的全球偶极场的变化特征,因而可用于建立下蜀黄土的年代标尺.新的年代标尺表明,大港钻孔的磁化率年代序列与北方黄土无法直接对比,证实了该地点的下蜀黄土磁化率变化机制与北方的不同.大港钻孔下蜀黄土的沉积速率与磁化率相关,低风尘沉积速率对应低磁化率,是降水增加所导致的结果.沉积速率与磁化率年代序列显示,下蜀黄土记录的本区季风变化过程可分为4个阶段.阶段Ⅳ(819～700ka)对应中更新世转型阶段,东亚季风降水较少.阶段Ⅲ(700～412ka)对应中更新世的大间冰期,东亚季风降水最多.阶段Ⅱ(412～197ka)时东亚季风降水减少,较阶段Ⅳ略少.阶段Ⅰ(197～34ka)东亚季风降水最少.因此,中更新世气候转型后,长时间尺度东亚季风降水持续减少,可能受全球温度阶段性降低驱动.  相似文献   

近2Ma来东菲律宾海地球磁场相对强度变化的沉积记录          下载免费PDF全文

孟庆勇  李安春  蒋富清  徐兆凯  朱友生  李德鹏 《海洋与湖沼》2010,41(4):606-613

为了解东菲律宾海沉积物记录的地球磁场相对强度变化,并为研究区的地层定年提供新的手段,对东菲律宾海帕里西维拉海盆西侧F090102孔柱样沉积物进行了系统的古地磁和岩石磁学分析。根据功率谱分析,选择非磁滞剩磁作为归一化的参数,得到约2Ma以来的地球磁场相对强度变化曲线。该曲线与SINT-2000曲线可详细对比,呈比较典型的锯齿状特征,布容期内的记录与800ka以来的SINT-800曲线相符。布容/松山极性转换期呈单强度降低的特征,在极性转换期和极性漂移期,相对强度曲线表现为显著低值。  相似文献   

降水与相对湿度协同算法研究          下载免费PDF全文

刘一玮  王彦  王庆元 《沙漠与绿洲气象(新疆气象)》2021,15(5):49-54

本文利用天津地区国家气象观测站2016-2017年常规观测数据和欧洲中心数值模式数据,建立降水和相对湿度协同统计订正算法并检验评估,结果表明：观测资料显示降水量级越小,其相对湿度的离散度越大,且日变化特征。雨量越大、降水持续时间越长,相对湿度稳定在90%以上。模式预报降水时的相对湿度分布离散度较大,需订正。基于降水与相对湿度的统计关系,建立的降水和相对湿度协同算法,算法对于小雨的相对湿度订正偏高,而对于中雨以上订正偏低；协同订正效果不理想的可能原因是模式数据的时间分辨率不高,协同统计算法还有待进一步优化。  相似文献