基于VAP卫星的等离子体层顶电子密度波动统计分析          下载免费PDF全文

王玉尤婷  张效信  何飞  林瑞淋  吕景天 《地球物理学报》2020,63(6):2141-2148

基于范艾伦辐射带探测卫星的观测数据(2012年9月至2015年11月),收集了584个等离子体层顶密度波动事件,研究了这些事件分布随磁地方时、磁壳值以及地磁活动的变化关系,并使用快速傅里叶变换分析了全部事件平均功率谱.统计结果表明,等离子体层顶密度波动事件主要发生在磁地方时黄昏扇区,其分布与磁地方时和地磁活动具有明显的相关性.等离子体层顶密度波动在1～100mHz区间内具有接近-5/3的功率谱斜率,表明存在二维磁流体动力学湍流.本文统计结果将有助于进一步深入理解等离子体层顶密度波动在内磁层中能量传输的具体作用,并且将促进对等离子体层顶波动的激发、增强与传播过程的进一步研究.  相似文献   

Approximate traveltime inversion in downhole microseismic monitoring     

Sergey Yaskevich  Anton A. Duchkov  Yuriy Ivanov 《Geophysical Prospecting》2020,68(3):918-925

In downhole microseismic monitoring, accurate event location relies on the accuracy of the velocity model. The model can be estimated along with event locations. Anisotropic models are important to get accurate event locations. Taking anisotropy into account makes it possible to use additional data – two S-wave arrivals generated due to shear-wave splitting. However, anisotropic ray tracing requires iterative procedures for computing group velocities, which may become unstable around caustics. As a result, anisotropic kinematic inversion may become time consuming. In this paper, we explore the idea of using simplified ray tracing to locate events and estimate medium parameters. In the simplified ray-tracing algorithm, the group velocity is assumed to be equal to phase velocity in both magnitude and direction. This assumption makes the ray-tracing algorithm five times faster compared to ray tracing based on exact equations. We present a set of tests showing that given perforation-shot data, one can use inversion based on simplified ray-tracing even for moderate-to-strong anisotropic models. When there are no perforation shots, event-location errors may become too large for moderately anisotropic media.  相似文献   

Separation of magnetic anomalies into induced and remanent magnetization contributions     

Jamaledin Baniamerian  Shuang Liu  Xiangyun Hu  Maurizio Fedi  Mahak Singh Chauhan  Mahmoud Ahmed Abbas 《Geophysical Prospecting》2020,68(7):2320-2342

Inversion of magnetic data is complicated by the presence of remanent magnetization, and it provides limited information about the magnetic source because of the insufficiency of data and constraint information. We propose a Fourier domain transformation allowing the separation of magnetic anomalies into the components caused by induced and remanent magnetizations. The approach is based on the hypothesis that each isolated source is homogeneous with a uniform and specific Koenigsberger ratio. The distributions of susceptibility and remanent magnetization are subsequently recovered from the separated anomalies. Anomaly components, susceptibility distribution and distribution of the remanent and total magnetization vectors (direction and intensity) can be achieved through the processing of the anomaly components. The proposed method therefore provides a procedure to test the hypotheses about target source and magnetic field, by verifying these models based on available information or a priori information from geology. We test our methods using synthetic and real data acquired over the Zhangfushan iron-ore deposit and the Yeshan polymetallic deposit in eastern China. All the tests yield favourable results and the obtained models are helpful for the geological interpretation.  相似文献   

基于两步弥散算子的共反射面元射线束成像方法研究          下载免费PDF全文

陈宝书  杨锴  汪小将 《地球物理学报》2020,63(1):270-286

基于克希霍夫统一成像理论,对共反射面元射线束成像方法进行了深入分析.通过这种分析可以得到一种新的共反射面元射线束类成像实现方式:基于两步弥散算子的共反射面元射线束类成像方法.当仅实施第一步弥散时,即可获得信噪比大幅提高同时更为规则的叠前道集.二维、三维的理论和实际数据算例证实了上述观点.  相似文献   

Holocene climate forcings and lacustrine regime shifts in the Indian summer monsoon realm     

Sushma Prasad  Norbert Marwan  Deniz Eroglu  Bedartha Goswami  Praveen K. Mishra  Birgit Gaye  A. Anoop  N. Basavaiah  Martina Stebich  Arshid Jehangir 《地球表面变化过程与地形》2020,45(15):3842-3853

Extreme climate events have been identified both in meteorological and long-term proxy records from the Indian summer monsoon (ISM) realm. However, the potential of palaeoclimate data for understanding mechanisms triggering climate extremes over long time scales has not been fully exploited. A distinction between proxies indicating climate change, environment, and ecosystem shift is crucial for enabling a comparison with forcing mechanisms (e.g. El-Niño Southern Oscillation). In this study we decouple these factors using data analysis techniques [multiplex recurrence network (MRN) and principal component analyses (PCA)] on multiproxy data from two lakes located in different climate regions – Lonar Lake (ISM dominated) and the high-altitude Tso Moriri Lake (ISM and westerlies influenced). Our results indicate that (i) MRN analysis, an indicator of changing environmental conditions, is associated with droughts in regions with a single climate driver but provides ambiguous results in regions with multiple climate/environmental drivers; (ii) the lacustrine ecosystem was ‘less sensitive’ to forcings during the early Holocene wetter periods; (iii) archives in climate zones with a single climate driver were most sensitive to regime shifts; (iv) data analyses are successful in identifying the timing of onset of climate change, and distinguishing between extrinsic and intrinsic (lacustrine) regime shifts by comparison with forcing mechanisms. Our results enable development of conceptual models to explain links between forcings and regional climate change that can be tested in climate models to provide an improved understanding of the ISM dynamics and their impact on ecosystems. © 2020 John Wiley & Sons, Ltd.  相似文献   

Geodynamic Model of the Neoproterozoic Evolution of the Yenisei Paleosubduction Zone (Western Margin of the Siberian Craton), Russia     

Kozlov  P. S.  Filippov  Yu. F.  Likhanov  I. I.  Nozhkin  A. D. 《Geotectonics》2020,54(1):54-67

Geotectonics - The article proposes a model of collisional and accretionary events of the Neoproterozoic at the western margin of the Siberian Craton based on the results of geological,...  相似文献   

堆积阶地古老滑坡识别方法及其在线状工程地质勘察中的应用     

安玉科  樊江  马胜午  马建全  高娟  毛立军 《吉林大学学报(地球科学版)》2020,50(6):1787-1794

阶地型古老滑坡体形成后，长期受各种营力影响，导致古老滑坡地貌形态破坏严重甚至消失。目前遥感技术和普通工程地质调绘很难发现这些滑坡的存在，给工程建设和后期运营造成较大安全隐患。为准确识别形态特征不明显的古老滑坡体，从阶地物质结构特征演变入手，找到阶地受剪切破坏产生的典型物质结构特征，将地层结构错断、卵砾石异常定向排列、摩擦镜面和泥包粒的眼球构造等作为滑坡准确识别依据。首先采用沿沟谷进行工程地质测绘的纵横交错追踪法确定滑坡体纵向范围和滑面形状，再结合地貌特征推测各级、块滑坡平面范围和分布，最后用点状勘探工程验证和校正推测结论。可将其总结为由"地貌异常、沿沟追踪、面上推断、点状校验"组成的阶地型滑坡识别方法，即物质结构异常推断法。结合线状工程勘察设计各阶段工作特点，提出线状工程前期工作中阶地型滑坡识别步骤，并在临渭高速公路工程建设项目中取得成功应用。  相似文献   

Middle Permian organic carbon isotope stratigraphy and the origin of the Kamura Event     

《Gondwana Research》2020

Large carbon cycle perturbations associated with the Middle Permian (Capitanian) mass extinction have been widely reported, but their causes and timing are still in dispute. Low resolution carbon isotope records prior to this event also limit the construction of a Middle Permian chemostratigraphic framework and global or local stratigraphic correlation, and hence limit our understanding of carbon cycle and environmental changes. To investigate these issues, we analyzed the ¹³C_org values from the Middle Permian chert-mudstone sequence (Gufeng Formation) in the Lower Yangtze deep-water basin (South China) and compared them with published records to build a chemostratigraphic scheme and discuss the underlying environmental events. The records show increased δ¹³C_org values from late Kungurian to early Guadalupian, followed by a decrease to the late Wordian/early Capitanian. The early-mid Capitanian was characterized by elevated δ¹³C_org values suggesting the presence of the “Kamura Event”: an interval of heavy positive values seen in the δ¹³C_carb record. We propose that these heavy Capitanian δ¹³C values may be a response to a marked decline in chemical weathering rates on Pangea and associated reduction in carbonate burial, which we show using a biogeochemical model. The subsequent negative δ¹³C excursion seen in some carbonate records, especially in shallower-water sections (and in a muted expression in organic carbon) coincide with the Capitanian mass extinction may be caused by the input of isotopically-light carbon sourced from the terrestrial decomposition of organic matter.  相似文献   

Disassociated feathers in Burmese amber shed new light on mid-Cretaceous dinosaurs and avifauna     

《Gondwana Research》2020

Even in the absence of associated skeletal material, isolated feathers in amber remain of high scientific interest. The remarkable preservation of these delicate structures in amber implies a potential for significantly improving our knowledge of feather evolution and diversity. A large sample set of 150 Burmese amber specimens (Upper Cretaceous, ~99 Ma) containing feathers is herein described. Several structural types can be differentiated, including flight feathers, contour feathers, semiplumes, and filoplumes. In some cases, peculiar pigmentation patterns and structural features can be documented. Additionally, different developmental stages have been captured in this assemblage with some examples of erupting feathers or neoptile plumage. Comparisons with previous studies, including skeletal material described in amber, show that Enantiornithes and non avialan dinosaurs are most likely represented in the assemblage, as well as unknown taxa.  相似文献   

Comprehensive Geological–Geophysical and Botanic Study of the Tectonic Junction Zone between the Katun Ridge and Uimon Depression (Altai Mountains)     

Boyarskikh  I. G.  Agatova  A. R.  Kulikova  A. I.  Bakiyanov  A. I.  Skaptsov  M. V.  Mazeika  J. 《Izvestiya Atmospheric and Oceanic Physics》2018,54(8):805-825

Izvestiya, Atmospheric and Oceanic Physics - Areas with large gradients and anomalous variations in geomagnetic and radiation fields have been revealed and mapped at the northwestern foot of the...  相似文献