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The source process of the 2014 Jinggu earthquake in Yunnan, China 2014年云南景谷地震的震源过程
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-06-15 DOI: 10.1016/j.pepi.2025.107410
Junlei Chen , Yan Li , Jinlai Hao , Tao Xu
The 2014 Jinggu Mw 6.0 earthquake occurred in the complex conjugate fault system of the Southwest Yunnan Block, comprised of NNW-trending and NNE-trending faults. We relocated the mainshock's hypocenter and inverted the focal mechanisms of earthquakes greater than M 3.5 and the mainshock's rupture process to study the earthquake sequence's source process. The relocation of the mainshock's hypocenter was determined to be at 100.47°E, 23.40°N, and 9.3 km. The focal mechanism of the mainshock is 150°/76°/179°(strike/dip/rake). There are 21 strike-slip earthquakes, 2 normal aftershocks, and 2 thrust aftershocks. The average dip angle of the Jinggu earthquake sequence is 78.75°. The Jinggu earthquake was a single-fault bilateral rupture event. The peak slip, average rake, and slip rate of the mainshock are 0.56 m, 182°, and 2.12 km/s, respectively. The main slip patch of the mainshock slip model was at 4 km in the 150° direction from the epicenter with a depth ranging from 4 km to 9 km. Ninety percent of the energy was released within the first 5.8 s. The Jinggu earthquake sequence may consist of ruptures on two fault planes dominated by the mainshock and two Mw 5.5 aftershocks occurring within the conjugate fault system.
2014年景谷6.0级地震发生在滇西南地块nnw向和nne向复杂共轭断裂体系中。我们重新定位了主震震源,反演了3.5级以上地震的震源机制和主震破裂过程,研究了地震序列的震源过程。主震震源定位于100.47°E, 23.40°N, 9.3 km。主震震源机制为150°/76°/179°(走向/倾斜/前倾)。共发生走滑地震21次,正常余震2次,逆冲余震2次。景谷地震序列的平均倾角为78.75°。景谷地震是一次单断层双侧破裂事件。主震的最大滑移量为0.56 m,平均前倾为182°,滑移率为2.12 km/s。主震滑动模型的主滑动块位于距震中150°方向4 km处,深度为4 ~ 9 km。百分之九十的能量是在最初的5.8秒内释放的。景谷地震序列可能由主震主导的两个断层面上的破裂和共轭断层系统内发生的两次5.5 Mw余震组成。
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引用次数: 0
Surface wave attenuation beneath the Himalaya-Tibet region constrained by fundamental mode of Rayleigh wave from the Hi-CLIMB dataset 基于Hi-CLIMB数据集的瑞利波基模态约束下的喜马拉雅-西藏地区地表波衰减
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-06-13 DOI: 10.1016/j.pepi.2025.107404
Davin David , Utpal Saikia , Ritima Das , Sarmistha Bhagawati
This study investigates Rayleigh wave group velocity and surface wave attenuation coefficients in the Himalaya-Tibet region using seismograms from 16 earthquakes recorded along the Hi-CLIMB network. The observed amplitude variations reveal a decreasing trend with distance, attributed to geometrical spreading, source radiation, wavefield scattering, and intrinsic attenuation. Attenuation coefficients range from 0.00167 km−1 to 0.00039 km−1 across the study area, while Rayleigh wave group velocities vary from 2.5 to 3.2 km/s for periods between 5 and 40 s. A strong frequency dependency in attenuation is observed, with attenuation coefficients peaking at shorter periods, consistent with similar trends reported in other tectonically active regions. Comparisons with global tectonic regions reveal higher attenuation beneath the study area, indicating low Q (41–82) values associated with mechanically weak, partially melted crust. The attenuation model suggests intrinsic attenuation as the dominant mechanism, though scattering effects cannot be ignored due to the region's structural complexity. Understanding these attenuation characteristics helps in interpreting seismic data and developing accurate ground motion prediction models, which are crucial for infrastructure resilience and early warning systems in this seismically active region. This, in turn, enhances seismic monitoring capabilities.
利用Hi-CLIMB台网记录的16次地震记录,研究了喜马拉雅-西藏地区的瑞利波群速度和面波衰减系数。由于几何扩散、源辐射、波场散射和本征衰减,观测到的振幅变化随距离的增加呈减小趋势。整个研究区域的衰减系数范围为0.00167 km−1至0.00039 km−1,而瑞利波群速度变化范围为2.5至3.2 km/s,周期为5至40 s。观测到衰减具有很强的频率依赖性,衰减系数在较短的周期内达到峰值,这与在其他构造活跃区域报道的类似趋势一致。与全球构造区相比,研究区下方的衰减更大,表明低Q值(41-82)与机械弱的部分熔融地壳有关。衰减模型表明本征衰减是主要机制,但由于区域结构的复杂性,散射效应也不能忽略。了解这些衰减特征有助于解释地震数据和开发准确的地面运动预测模型,这对地震活跃地区的基础设施恢复能力和早期预警系统至关重要。这反过来又增强了地震监测能力。
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引用次数: 0
Mechanisms of two P-phase observations in earthquakes within the upper mantle beneath Northeast Taiwan: Insights from 2D waveform simulations 台湾东北部上地幔地震的两次p相观测机制:来自二维波形模拟的见解
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-06-13 DOI: 10.1016/j.pepi.2025.107409
Hung-Yu Yen , Po-Fei Chen , Mei Chien
Understanding the upper mantle structures beneath northeast Taiwan is crucial for interpreting the region's geodynamics. The deployment of the Formosa Array since 2017 has facilitated this investigation. In this study, we thoroughly examine the observations of two P phases from a representative deep earthquake, starting with a compilation of arrival time patterns and waveform characteristics, followed by two-dimensional waveform simulations. After successfully reproducing the key observations using models that include a high Vp anomaly in the mantle wedge above the Ryukyu subduction zone and a slightly faster Eurasian lithosphere to the west, we conclude that the second P phase originates from a head wave along the sub-vertical boundary of the Eurasian lithosphere. These two-dimensional model structures also replicate the observed arrival time patterns of nearby events with two P phases. The results of this study provide alternative constraint on the boundary between the Philippine Sea Plate and the Eurasian Plate at the surface. The findings support the active role of the Eurasian Plate in accommodating the northwesterly-indented Philippine Sea Plate slab beneath northeast Taiwan, rather than a passively torn model.
了解台湾东北部的上地幔结构对于解释该地区的地球动力学至关重要。自2017年以来,福尔摩沙阵列的部署为这项调查提供了便利。在这项研究中,我们从一个具有代表性的深地震的两个P相观测开始,从到达时间模式和波形特征的汇编开始,然后是二维波形模拟。在使用包括琉球俯冲带上方地幔楔的高Vp异常和西面稍快的欧亚岩石圈在内的模型成功再现了关键观测结果后,我们得出结论,第二次P相起源于沿欧亚岩石圈亚垂直边界的头波。这些二维模型结构也复制了观测到的具有两个P相的附近事件的到达时间模式。这一研究结果为菲律宾海板块与欧亚板块之间的表面边界提供了替代约束。研究结果支持欧亚板块对台湾东北下方菲律宾海板块的主动容纳作用,而非被动撕裂模式。
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引用次数: 0
Frequency characteristics of electrical conductivity anomalies and the coastal effect 电导率异常的频率特性与海岸效应
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-06-12 DOI: 10.1016/j.pepi.2025.107400
Igor I. Rokityansky, Artem V. Tereshyn
<div><div>In geophysical studies of the electrical conductivity of the Earth's crust and upper mantle, quantitative integral parameters describing the scale/intensity of electrical conductivity anomalies are almost not used yet. A simple and informative parameter is the total lengthwise conductance G = Q∙ϭ<sub>i</sub>, where Q is the cross-section area of the anomalous body and ϭ<sub>i</sub> is its conductivity. In the Earth's lithosphere, anomalous fields are excited/aroused mainly by the conductive mechanism, for which a theory was developed (<span><span>Rokityansky, 1972</span></span>; <span><span>Rokityansky, 1975a</span></span>, <span><span>Rokityansky, 1975b</span></span>; <span><span>Rokityansky, 1982</span></span>). This theory links G to the frequency characteristic of the anomalous field or more specifically with the period T<sub>0</sub> at which the real part of the anomalous field reaches a maximum and the imaginary part is equal to 0, changing sign. The anomalous field is mainly represented by the induction arrow. One of the main objectives of this work is to specify the relationship between the observed value T<sub>0</sub> and the desired G under real Earth conditions, that is, to determine the function G (T<sub>0</sub>). Estimating G is important for several factors: 1. Any additional parameter enhances a study's possibilities. 2. A highly reliable quantity G determined by magnetic variation profiling allows using it as <em>a priori</em> information for subsequent computer interpretation of 5-component records. 3. The availability of a quantitative characteristic allows ordering anomalies according to their scale/intensity. The method was first described in 1975 in PEPI, but it was based on simplified Earth models, and the dependence G(T<sub>0</sub>) was obtained with an error exceeding half an order of magnitude. This paper presents results of new 2D models calculations which were as close as possible to typical Earth structures and the error was reduced by approximately three times. The main models were deep conductors with a compact cross-section and surface conductors represented by rectangular seawater layer of varying depths, forming a coastal effect. In a complicated model of the deep (4000 m) sea with the shelf (100 km wide, 200 m deep), a previously unknown phenomenon was discovered - a very local increase in the anomalous field in the coastal zone of land, which we termed the resonance-synergistic effect. The paper further presents results of 137 observatories of the INTERMAGNET network processing, covering for the first time all latitudes from the Arctic Ocean to Antarctica. At all observatories, induction arrows were calculated for periods of 225, 450, 900, 1800 and 3000 s. Five coastal observatories with induction arrows exceeding 0.8 are shown on maps along with the bathymetry of the adjacent seas. The analysis demonstrated that the regularities calculated on 2D models explain the main patterns of behavior observed ne
在地壳和上地幔电导率的地球物理研究中,描述电导率异常尺度/强度的定量积分参数几乎尚未被使用。一个简单且信息丰富的参数是总纵向电导G = Q∙ϭi,其中Q为异常体的横截面积,ϭi为异常体的电导。在地球岩石圈中,异常场主要是由导电机制激发的,对此已经发展了一种理论(Rokityansky, 1972;罗基提扬斯基,1975a,罗基提扬斯基,1975b;Rokityansky, 1982)。该理论将G与异常场的频率特性联系起来,或者更具体地说,与周期T0联系起来,在T0处异常场的实部达到最大值,虚部等于0,改变符号。异常场主要由感应箭头表示。本工作的主要目标之一是确定实际地球条件下观测值T0与期望G之间的关系,即确定函数G (T0)。估计G对于以下几个因素很重要:任何额外的参数都增强了研究的可能性。2. 由磁变剖面确定的高度可靠的量G允许将其用作随后计算机解释五分量记录的先验信息。3. 定量特征的可用性允许根据其规模/强度对异常进行排序。该方法于1975年在PEPI中首次描述,但它是基于简化的地球模型,并且获得的相关性G(T0)误差超过半个数量级。本文介绍了新的二维模型的计算结果,该模型尽可能接近典型的地球结构,误差减少了大约三分之一。主要模型为截面紧凑的深层导体和以不同深度的矩形海水层为代表的表层导体,形成海岸效应。在深海(4000米)与大陆架(100公里宽,200米深)的复杂模型中,发现了一个以前未知的现象-陆地沿海地区异常场的非常局部的增加,我们称之为共振协同效应。本文进一步介绍了INTERMAGNET网络处理的137个观测站的结果,首次覆盖了从北冰洋到南极洲的所有纬度。在所有天文台中,分别计算了225、450、900、1800和3000 s周期的诱导箭头。地图上显示了五个感应箭头超过0.8的沿海天文台,以及邻近海域的水深测量图。分析表明,在二维模型上计算的规律解释了用明确的三维测深法在近海观测到的主要行为模式。在两个沿海观测站的数据中发现了共振-协同效应。使用G(T0)方法获得的最基本的结果是,T0大于5000 s的异常(因此G >;2∙109 S∙m)。显然,在地球的岩石圈中不存在这样和更大的导电性。
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引用次数: 0
Evaluation of archeo- and paleomagnetic field models and their common features 古、古磁场模型的评价及其共同特征
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-06-09 DOI: 10.1016/j.pepi.2025.107399
Ingo Wardinski , Filipe Terra-Nova , Erwan Thébault
Archeo- and paleomagnetic field models show a wide range of temporal variability and of spatial content. While the temporal variability may reflect true geomagnetic field variation, the different spatial content of individual models could be explained by different modeling strategies and data sources, but mostly by data uncertainties. To overcome these data uncertainties, we derive averaged models over the last 100 kyrs from a large suite of different archeo- and paleomagnetic field models using different average techniques. The averaged models allow us to evaluate the robustness and the significance of spatial features of these models throughout time. It is utilized to compute structural criteria that quantify the axial dipole dominance, the equator-symmetry of magnetic field, its zonality and other important measures of weak field regions and control of the geodynamo by heterogeneous heat flux at the lowermost mantle. These criteria are used to quantify the Earth-likeness of numerical dynamo simulations. Over 100 kyrs the criteria show larger fluctuations than previously assumed, which implies a wider range of numerical dynamo simulations to be considered Earth-like.
太古和古磁场模式显示出广泛的时间变异性和空间内容。虽然时间变率可以反映真实的地磁场变化,但不同的建模策略和数据源可以解释各个模型的不同空间内容,但主要是数据的不确定性。为了克服这些数据的不确定性,我们使用不同的平均技术,从一套不同的古代和古磁场模型中得出了过去100年的平均模型。平均模型使我们能够评估这些模型在整个时间内的稳健性和空间特征的重要性。利用它计算了量化轴向偶极子优势、磁场赤道对称、地带性等弱场区和最下层地幔非均质热通量对地球动力控制的重要指标的结构准则。这些准则用于量化数值发电机模拟的地球相似度。在100多年的时间里,标准显示出比先前假设的更大的波动,这意味着更大范围的数值发电机模拟被认为是类地的。
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引用次数: 0
Crystallographic preferred orientation of (Mg,Fe)O up to 125 GPa inferred from torsional deformation experiments using a rotational diamond anvil cell (Mg,Fe)O在高达125 GPa时的晶体优选取向,由旋转金刚石砧细胞的扭转变形实验推断
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-06-06 DOI: 10.1016/j.pepi.2025.107392
Bunrin Natsui , Shintaro Azuma , Keishi Okazaki , Kentaro Uesugi , Masahiro Yasutake , Saori Kawaguchi-Imada , Ryuichi Nomura , Kenji Ohta
To investigate the texture development of (Mg,Fe)O, we conducted torsional deformation experiments on (Mg,Fe)O with varying Fe contents under pressures up to 125 GPa and temperatures up to 900 K using a rotational diamond anvil cell combined with synchrotron X-rays. The results indicate that the texture development follows the same trend as that observed in MgO, even when the Fe content varies or undergoes a spin transition. However, we found that the crystal plane perpendicular to the compression direction of (Mg,Fe)O could transition from {110} to {100} at lower pressure and temperature conditions than in MgO, attributable to the effect of Fe incorporation. Additionally, the texture of (Mg,Fe)O may vary with the combination of Fe content and strain. In regions with high Fe content and large strains, such as the D″ layer, it may be necessary to evaluate the seismic anisotropy of (Mg,Fe)O based on the texture considering the effects of Fe content and strain.
为了研究(Mg,Fe)O的织构发展,我们利用旋转金刚石砧细胞结合同步加速器x射线,在高达125 GPa的压力和高达900 K的温度下,对不同铁含量的(Mg,Fe)O进行了扭转变形实验。结果表明,当Fe含量发生变化或发生自旋转变时,织构的发展趋势与MgO相同。然而,我们发现垂直于(Mg,Fe)O压缩方向的晶面在较低的压力和温度条件下可以从{110}转变为{100},这是由于Fe掺入的影响。此外,(Mg,Fe)O的织构随铁含量和应变的变化而变化。在高铁含量和大应变的区域,如D″层,考虑铁含量和应变的影响,可能有必要基于织构评价(Mg,Fe)O的地震各向异性。
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引用次数: 0
Porosity and hydrous alteration of the Martian crust from InSight seismic data 洞察号地震数据显示的火星地壳孔隙度和含水蚀变
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-05-29 DOI: 10.1016/j.pepi.2025.107383
Brigitte Knapmeyer-Endrun , Ludmila Adam , Sebastian Carrasco , Matthew P. Golombek , Doyeon Kim , Martin Knapmeyer , Katarina Miljković , Ana-Catalina Plesa , Nicholas H. Warner , Mark Wieczorek
The composition and layering of the Martian crust provide important constraints on planetary crustal evolution as well as on present-day conditions, e.g., with regard to the presence of liquid water or ice. The seismic data of the InSight mission yielded new and critical information on crustal structure at several locations on Mars. Here, we use rock physical models to investigate the range of lithologies, porosities and alteration scenarios compatible with seismic P- and S-wave velocities as well as vP/vS ratios from InSight. We find that present-day crustal porosity extends to 20–25 km depth at all sampled locations, with large Noachian impacts as main drivers for the creation of porosity, and viscous pore closure as likely agent of removal of porosity at depth, resulting in a discontinuous increase in seismic velocities. Spatially heterogeneous seismic velocities can be related to differences in porosity that could be caused by subsequent localized magmatic activity. At the InSight landing site, where seismic data indicate a four-layered crust, hydrated minerals as traces of aqueous alteration are present throughout the crust, though the water within these minerals could be fairly limited at 0.3 wt% or less. The most likely types of hydrated minerals are also consistent with a post-depositional environment that was limited in water. The velocity increase at about 10 km depth beneath InSight can either be attributed to a change in composition from felsic to basaltic, or to a change in porosity by the deposition of Utopia ejecta. A felsic component to the crust, e.g. due to impact-generated buoyant partial melts, can accordingly not be excluded, but would not be present globally. Seismic and geological constraints for the layer at approximately 200 m to 2000 m depth beneath the lander strongly favor basaltic Noachian sediments saturated with a mixture of up to 10 % ice and brine. However, the lateral extent of this present day aquifer is not constrained by the available data.
火星地壳的组成和分层对行星地壳的演化以及目前的条件,例如液态水或冰的存在,提供了重要的限制。洞察号任务的地震数据为火星上几个地点的地壳结构提供了新的关键信息。在这里,我们使用岩石物理模型来研究与InSight地震P波和s波速度以及vP/vS比兼容的岩性、孔隙度和蚀变情景范围。我们发现,在所有采样点,现今地壳孔隙度延伸至20-25 km深度,大的诺亚亚影响是孔隙度产生的主要驱动因素,而粘性孔隙封闭可能是深度孔隙度去除的因素,导致地震速度不连续增加。空间非均质地震速度可能与孔隙度差异有关,孔隙度差异可能由随后的局部岩浆活动引起。在洞察号的着陆点,地震数据显示有四层地壳,水合矿物作为水蚀变的痕迹存在于整个地壳中,尽管这些矿物中的水含量可能相当有限,只有0.3 wt%或更少。最可能的水合矿物类型也与沉积后的水有限环境相一致。在“洞察号”地下约10公里深处,速度的增加可以归因于组成从长英质到玄武岩的变化,也可以归因于乌托邦喷出物沉积导致孔隙度的变化。因此,不能排除地壳中的英质成分,例如由于撞击产生的浮力部分熔体,但不会在全球范围内存在。在着陆器下约200米至2000米深度的地层中,地震和地质条件的限制强烈支持玄武质诺阿奇亚沉积物,其中饱和了高达10%的冰和盐水混合物。然而,目前这一含水层的横向范围不受现有数据的限制。
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引用次数: 0
The effect of source-side subduction on PKP differential times and implications for inner core anisotropy 源侧俯冲对PKP微分时间的影响及其对内核各向异性的启示
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-05-29 DOI: 10.1016/j.pepi.2025.107382
Stuart Russell , John Keith Magali , Kimberly Vallenton , Christine Thomas
Directional variation in PKP differential times provides compelling evidence that Earth's inner core is anisotropic. These phases, however, are also sensitive to Earth's heterogeneous mantle. Disentangling the causal structures of PKP differential time anomalies is difficult but nonetheless important if we are to fully understand the structure and evolution of Earth's inner core. A large proportion of earthquakes used to study the inner core originate from subduction zones, which are associated with strongly positive upper mantle seismic velocity anomalies, but the effect of these on the measurements has not yet been investigated.
In this study, we use AxiSEM3D to simulate the effect of source-side subduction on PKP differential time measurements. We find that some combinations of slab parameters result in artefacts up to several seconds in magnitude, while for others the effect is negligible. We subsequently examine existing data sets of measurements to assess if source-side subduction has a detectable influence on the data, and also to assess if the Scotia slab is the cause of observed anomalous measurements originating from the South Sandwich Islands. We find that the signal of source-side subduction in the data is possibly present but weak, and that the magnitude of anisotropy required by the data is not affected by source-side subduction. Furthermore, the Scotia slab is unlikely to be the cause of the anomalous measurements from the South Sandwich Islands. Nevertheless, we advise caution for future studies as the artefacts caused by source-side subduction may, in some cases, be significant.
PKP差异时间的方向变化提供了令人信服的证据,证明地球内核是各向异性的。然而,这些阶段对地球的非均质地幔也很敏感。解开PKP微分时间异常的因果结构是困难的,但如果我们要充分了解地球内核的结构和演化,这一点仍然很重要。用于研究内核的大部分地震来自于俯冲带,这与强烈的正上地幔地震速度异常有关,但这些对测量的影响尚未得到研究。在本研究中,我们使用AxiSEM3D模拟了源侧俯冲对PKP差分时间测量的影响。我们发现,一些组合的板参数导致人工高达几秒钟的大小,而对其他的影响是可以忽略不计的。随后,我们检查了现有的测量数据集,以评估源侧俯冲是否对数据有可探测的影响,并评估Scotia板块是否是观测到的源自南桑威奇群岛的异常测量的原因。我们发现资料中可能存在震源侧俯冲的信号,但信号较弱,资料所要求的各向异性大小不受震源侧俯冲的影响。此外,斯科舍板块不太可能是南桑威奇群岛测量异常的原因。然而,我们建议对未来的研究保持谨慎,因为在某些情况下,由源侧俯冲引起的伪影可能很重要。
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引用次数: 0
Kinetic energy transfer during polarity reversals in a numerical dynamo simulation 数值发电机模拟极性反转过程中的动能传递
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-05-23 DOI: 10.1016/j.pepi.2025.107384
Takumi Kera , Hiroaki Matsui , Masaki Matsushima , Yuto Katoh
The Earth has a magnetic field with a dominant dipole moment nearly parallel to the axis of Earth's rotation. It is widely accepted that the geomagnetic field is sustained by fluid motion in the Earth's outer core, the so-called dynamo action. Paleomagnetic measurements have shown that the geomagnetic field has reversed its polarity many times. Some geodynamo simulations have been carried out to investigate the physical process of polarity reversals, and the equatorially antisymmetric flow during polarity reversals is found to be stronger than that during stable periods. On the other hand, convective motions in a rotating spherical shell have characteristics that the equatorially symmetric flow is dominant due to the effect of the Earth's rotation. To investigate energy transfers between the equatorially symmetric and antisymmetric flows in the dipole reversals, we have performed geodynamo simulations with polarity reversals. The energy transfer to the equatorially antisymmetric flow is generally small comparing with the buoyancy flux to the equatorially symmetric flow. Toward a polarity reversal, however, it increases in the following manner; (i) the rate of energy transfer from the equatorially symmetric flow to the magnetic field decreases, (ii) the rate of energy transfer from the equatorially symmetric flow to the antisymmetric flow by the advection increases, and (iii) the energy injection by the buoyancy force into the equatorially antisymmetric flow increases. The present results suggest that the intense zonal flow caused by the intense upward flow inside the tangent cylinder in the either hemisphere can trigger a polarity reversal of the magnetic field.
地球磁场的主导偶极矩几乎平行于地球自转轴。人们普遍认为,地磁场是由地球外核的流体运动维持的,即所谓的发电机作用。古地磁测量表明,地磁场的极性多次逆转。通过地球动力学模拟研究了极性逆转的物理过程,发现极性逆转期间的赤道不对称流比稳定期强。另一方面,由于地球自转的影响,旋转球壳中的对流运动具有等对称流占主导地位的特点。为了研究偶极反转中等对称和反对称流之间的能量传递,我们进行了具有极性反转的地球动力学模拟。相对于平等不对称流的浮力通量,能量传递到平等不对称流的能量传递通常较小。然而,对于极性反转,它以以下方式增加;(1)赤道对称流向磁场传递能量的速率减小;(2)平流向反对称流传递能量的速率增大;(3)浮力向赤道反对称流注入能量的速率增大。目前的结果表明,由切线圆柱内强烈的向上流动引起的强烈的纬向流动可以触发磁场的极性反转。
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引用次数: 0
Edges of thermochemical structures in the lower mantle 下地幔热化学结构的边缘
IF 2.4 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2025-05-21 DOI: 10.1016/j.pepi.2025.107381
Mo Hu, Michael Gurnis
Global seismic tomography consistently identifies two large low shear velocity provinces (LLSVPs) beneath Africa and the Pacific in the lower mantle. These structures are generally hypothesized to have a thermochemical origin with a higher bulk modulus (K) than ambient mantle. Regional high-resolution seismic studies have revealed that LLSVPs exhibit diverse edge morphologies, though the factors controlling these variations remain unclear. Here we quantitatively investigate the evolution of LLSVP boundary topographies through high-K thermochemical convection models. The calculations show that the boundary morphology of a thermochemical pile is primarily controlled by its density and viscosity. Comparison with observed boundary shapes suggests that the African LLSVP may be less dense and thus less stable than the Pacific LLSVP, potentially reflecting differences in their compositions and evolutions. Additionally, the observed boundary complexity indicates that the viscosity of LLSVPs is likely no more than an order of magnitude higher than that of the surrounding mantle.
全球地震层析成像一致地确定了非洲和太平洋下地幔下两个大的低剪切速度省(llsvp)。这些结构通常被假设为具有比周围地幔更高的体积模量(K)的热化学起源。区域高分辨率地震研究表明,llsvp具有不同的边缘形态,但控制这些变化的因素尚不清楚。本文通过高k热化学对流模型定量研究了LLSVP边界地形的演化。计算表明,热化学桩的边界形态主要受其密度和粘度的控制。与观测到的边界形状比较表明,非洲LLSVP可能密度较低,因此比太平洋LLSVP更不稳定,这可能反映了它们在组成和演化方面的差异。此外,观察到的边界复杂性表明,llsvp的粘度可能不超过周围地幔的一个数量级。
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Physics of the Earth and Planetary Interiors
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