Axisymmetric wave propagation in multilayered poroelastic grounds due to a transient acoustic point source     

《Soil Dynamics and Earthquake Engineering》2013

This paper deals with the study of axisymmetric wave propagation in various acoustic/porous stratified media coupling configurations. It presents the theoretical developments of a semi-analytical method, its validation for a limit test-case half-space ground, and an extension to a realistic multilayered seabed, when spherical waves are emitted from a transient point source in water.  相似文献   

Soldiers Cap Group iron‐formations,Mt Isa Inlier,Australia, as windows into the hydrothermal evolution of a base‐metal‐bearing Proterozoic rift basin     

O. J. Hatton  G. J. Davidson 《Australian Journal of Earth Sciences》2013,60(1):85-106

The Proterozoic Soldiers Cap Group, a product of two major magmatic rift phases separated by clastic sediment deposition, hosts mineralised (e.g. Pegmont Broken Hill‐type deposit) and barren iron oxide‐rich units at three main stratigraphic levels. Evaluation of detailed geological and geochemical features was carried out for one lens of an apatite‐garnet‐rich, laterally extensive (1.9 km) example, the Weatherly Creek iron‐formation, and it was placed in the context of reconnaissance studies of other similar units in the area. Chemical similarities with iron‐formations associated with Broken Hill‐type Pb–Zn deposit iron‐formations are demonstrated here. Concordant contact relationships, mineralogy, geochemical patterns and pre‐deformational alteration all indicate that the Soldiers Cap Group iron‐formations are mainly hydrothermal chemical sediments. Chondrite normalised REE patterns display positive Eu and negative Ce anomalisms, are consistent with components of both high‐temperature, reduced, hydrothermal fluid (≥250°C) and cool oxidised seawater. Major element data suggest a largely mafic provenance for montmorillonitic clays and other detritus during chemical sedimentation, consistent with westward erosion of Cover Sequence 2 volcanic rocks, rather than local mafic sources. Ni enrichment is most consistent with hydrogenous uptake by Mn‐oxides or carbonates. Temperatures inferred from REE data indicate that although they are not strongly enriched, base metals such as Pb and Zn are likely to have been transported and deposited prior to or following iron‐formation deposition. Most chemical sedimentation pre‐dated emplacement of the major mafic igneous sill complexes present in the upper part of the basin. Heating of deep basinal brines in a regional‐scale aquifer by deep‐seated mafic magma chambers is inferred to have driven development of hydrothermal fluids. Three major episodes of extension exhausted this aquifer, but were succeeded by a final climactic extensional phase, which produced widespread voluminous mafic volcanism. The lateral extent of the iron‐formations requires a depositional setting such as a sea‐floor metalliferous sediment blanket or series of brine pools, with iron‐formation deposition likely confined to much smaller fault‐fed areas surrounded by Fe–Mn–P–anomalous sediments. These relationships indicate that in such settings, major sulfide deposits and their associated chemical sediment marker horizons need not overlie major igneous sequences. Rather, the timing of expulsion of hydrothermal fluid reflects the interplay between deep‐seated heating, extension and magmatism.  相似文献   

Evidence for Long-term Retrograde Motions of Sunspot Patterns and Indications of Coupled g-mode Rotation Rates     

David A. Juckett  Charles L. Wolff 《Solar physics》2008,252(2):247-266

Solar g-modes are global oscillations that would exist primarily in the radiative zone (RZ) and would be excited by either convective overshoot or nuclear burning in the core. Wolff and O’Donovan (Astrophys. J. 661, 568, 2007) proposed a non-linear coupling of g-modes into groups that share the same harmonic degree ℓ. Each group (denoted set(ℓ)) exhibits a unique retrograde rotation rate with respect to the RZ that depends mainly on ℓ. The coupling yields a standing wave (nearly stationary in longitude) that has two angularly defined hot spots offset from the equator on opposite sides of the Sun that would deposit energy asymmetrically in the lower convective envelope (CE). It is anticipated that when two or more groups overlap in longitude, an increase in local heating would influence the distribution of sunspots. In this paper, we scanned a multitude of rotational reference frames for sunspot clustering to test for frames that are concordant with the rotation of these g-modes sets. To achieve this, spherical harmonic filtering of sunspot synoptic maps was used to extract patterns consistent with coalesced g-modes. The latitude band, with minimal differential rotation, was sampled from each filtered synoptic map and layered into a stackplot. This was progressively shifted, line-by-line, into different rotational reference frames. We have detected long-lived longitudinal alignments, spanning 90 years of solar cycles, which are consistent with the rotation rate of the deep solar interior as well as other rotational frames predicted by the coupled g-mode model. Their sidereal rotation rates of 370.0, 398.8, 412.7, 418.3, 421.0, 424.2 and 430.0 nHz correspond, respectively, to coupled g-modes for ℓ = 2 through 7 and G, where G is a set with high ℓ values or a group of such sets (unresolved) that rotate almost as fast as the RZ. While the clustering in these reference frames offers new approaches for studying the longitudinal behavior of solar activity, it tentatively leads to the more profound conclusion that a portion of the driving force for sunspot occurrence is linked to energy extracted from the solar core and deposited at the top of the RZ by solar g-modes.  相似文献   

数字化水位仪观测的苏门答腊大地震激发的地球球型自由振荡   总被引：2，自引：0，他引：2  

任佳  陈华静  蒋翠荣  王松  温超  杨耀文  王长江 《地震研究》2009,32(4)

利用LN-3型数字化水位仪的观测资料,采用功率谱密度估计方法,在没有对资料进行去固体潮处理的情况下,获得了2004年12月26日苏门答腊大地震激发的0S3～0S30基频球型自由振荡,并检测到2S1、1S2、1S3、2S5和2S6等5个谐频球型振荡,同时记录到一些明显的振型的谱线分裂现象。用水位观测资料提取了0S3、0S4和2S1等3个振型的谱线分裂周期,虽然3个振型均只得到2个单峰,但地球自由振荡谱线分裂现象的检测为研究地球的深内部结构提供了新的、不同类型的观测资料。研究表明,用数字化水位仪的观测资料可以提取到苏门答腊大地震激发的地球球型振荡,为地球自由振荡的研究提供了一种新的观测手段。  相似文献   

地震地磁监测试验区研究进展          下载免费PDF全文

张毅  顾左文  顾春雷  朱志春  王雷  徐如刚  陈斌 《地震工程学报》2009,31(4):393-396,402

主要从中国地震地磁监测试验区的现况、数据观测与处理、模型计算方法以及监测成果等方面介绍了研究进展.通过对地震地磁试验区的探索性研究,分析了开展监测试验区研究的重要意义,展望了其发展前景.  相似文献   

基于多尺度球面小波解算GPS应变场的方法及应用          下载免费PDF全文

苏小宁  孟国杰  王振 《地球物理学报》2016,59(5):1585-1595

提出了利用多尺度球面小波解算GPS应变场的方法,该方法通过建立不规则分布的小波基函数以凸显测站非均匀分布的特征,获取不同空间尺度的应变场.通过对模拟数据进行对比分析验证该方法的有效性,模拟结果显示,多尺度球面小波应变计算方法稳健性较好.在位移场中加入高斯随机误差(均值为0.0mm,标准差为0.5mm)对应变计算结果的影响可忽略不计.从原有位移场随机抽取的60%的数据解算应变场时,仍然能够获取比较可靠的结果,但如果出现大范围的数据空缺,则会对应变结果产生明显影响.基于华北地区GPS测站原始观测数据,通过高精度数据处理方法解算了该区域GPS速度场,根据多尺度球面小波方法,解算了该区域的应变率场及其误差,并分析了其空间分布特征.  相似文献   

基于微粒变化对崇测冰帽浅层冰芯的定年结果   总被引：6，自引：1，他引：5  

韩建康  中尾正义  东久美子  张万昌  和田熏  朱丰年 《冰川冻土》2005,27(6):846-852

冰芯年代学的建立, 对于稳定同位素定年方法失效的钻点尤为困难. 依据粒径在0.66～1.33μm之间的不可溶尘埃微粒的浓度垂向分布, 并结合阳离子Ca2 的浓度剖面变化, 实现了对崇测冰帽冰芯浅层的断代. 该冰芯钻自海拔6 532 m的冰穹顶部, 解析的18.7 m冰芯长度占到钻点冰层深度约2/5, 辅助的定年参数包括钻点表层5 a的实测净积累率和大气核试验的地层标志. 综合各种技巧定年, 崇测冰帽该冰芯覆盖的记录年代为1902-1992年, 最底部累积误差在±2 a(约为2%).  相似文献   

Simultaneous determination of global topography, tidal Love number and libration amplitude of Mercury by laser altimetry     

Christian Koch  Ulrich Christensen  Reinald Kallenbach 《Planetary and Space Science》2008,56(9):1226-1237

Solar tidal forces generate elevation changes of Mercury's surface of the order 1 m within one Hermean year, and solar torques on the non-symmetric permanent mass distribution of the planet cause an uneven rotation of Mercury's surface with a libration amplitude of the order of 40 arcsec. Knowledge of the precise reaction of the planet to tidal forcing, expressed by the Love numbers h₂ and k₂, as well as accurate knowledge of the amplitude of forced libration Φ_lib, puts constraints on the internal structure, for example the state and the size of the core. The MESSENGER and BepiColombo missions to Mercury carry laser altimeters, whose primary goal is to accurately map the topography. Here we investigate if the Love number h₂ and the amplitude of forced libration can be determined together with the static topography of the planet from a global altimetry record. We do this by creating synthetic altimeter data for the nominal orbit of BepiColombo over the nominal mission duration of approximately four Mercury years and inverting them for the static and time-dependent parts of the topography. We assume purely Gaussian noise. We find that it is possible to extract both parameters h₂ and Φ_lib with an accuracy of approximately 10%, while the static topography coefficients of a spherical harmonic expansion can be determined simultaneously with an accuracy at the centimetre level. Extraction of the static topography to higher harmonic degrees improves the precision of the measurement of h₂ and Φ_lib. The simulation results demonstrate that it seems feasible to test current models on Mercury's interior with sufficient precision using BepiColombo Laser Altimeter data.  相似文献   

Histological assessment of variations in sexual maturity of cod (Gadus morhua L.) at the Flemish Cap (north-west Atlantic)     

Saborido-Rey  Fran; Junquera  Susana 《ICES Journal of Marine Science》1998,55(3):515-521

  相似文献   

局部重力场球冠谐分析中的导数计算及应用     

吴招才  刘天佑  高金耀 《海洋与湖沼》2006,37(6):488-492

在建立局部地区的地球重力场模型中,球冠谐分析是一种有效的方法。在球冠坐标系下建立重力场模型时,仅涉及到重力位的垂向分量,不必进行关于极角的微分运算,所以仅用单个正交基来建模,但若要在球冠坐标系下对重力场作进一步分析,如类似于平面处理的导数运算,来突出地质体的边界,要计算极角的微分,利用单个正交基表示则不易收敛,且误差较大。本文中作者采用两个正交基函数在球冠坐标系下对重力场建模,推导计算了径向导数和曲面导数模,并利用棱柱体正演模型进行检验,结果表明双基函数建模更适合曲面上的位场表示。最后计算了冲绳海槽地区卫星测高重力异常数据的曲面导数,径向导数清晰划分了东海陆架上大构造单元,曲面导数梯度带显示了东海陆架外缘隆起带,也指示了陆架盆地内的一些局部构造。这表明双基函数的球冠谐分析是一种有效的曲面位场建模方法。  相似文献