2017年四川九寨沟M_S7.0强震的余震重定位及主震震源机制反演          下载免费PDF全文

梁姗姗  雷建设  徐志国  徐锡伟  邹立晔  刘敬光  陈宏峰 《地球物理学报》2018,61(5):2163-2175

本文采用双差定位法对2017年8月8日至10月31日期间四川九寨沟M_S7.0主震及5200个余震序列进行相对定位，得到4036个重定位地震事件.采用中国区域地震台网观测到的宽频带垂直分向波形数据和W震相反演方法，得到了主震震源机制解.重定位结果显示，余震序列分别沿NNW和SSE两个方向扩展，展布长度约58 km，且这些余震主要集中在22 km深度之上.余震分布的另一个重要特点是具有分区特性，即在主震NNW方向约5 km处存在明显的西北和东南两区余震活动分界线；西北区的余震由深至浅具有较好连续性，而东南区却在约10 km深度处存在不连续性.余震分布的这种分区特征，说明九寨沟地震震源区的地壳结构存在强烈的不均匀性.余震分布与主震破裂特征的一致性，证实了我们定位结果的可靠性.主震的震源机制解展示出节面Ⅰ的走向/倾角/滑动角分别为246°/83.7°/-177°，而节面Ⅱ的走向/倾角/滑动角为155.7°/87.1°/-6.3°，最佳质心深度为15.5 km，矩震级M_W为6.5.根据余震分布较为垂直和主震震源机制解两节面的倾角均在80°以上，并结合野外地质调查结果，推测此次九寨沟地震为与节面Ⅱ参数相近的一次高角度的左旋走滑型事件.  相似文献   

Analytical and empirical models for predicting the drift capacity of modern unreinforced masonry walls     

Bastian Valentin Wilding  Katrin Beyer 《地震工程与结构动力学》2018,47(10):2012-2031

Displacement‐based seismic assessment of buildings containing unreinforced masonry (URM) walls requires as input, among others, estimates of the in‐plane drift capacity at the considered limit states. Current codes assess the drift capacity of URM walls by means of empirical models with most codes relating the drift capacity to the failure mode and wall slenderness. Comparisons with experimental results show that such relationships result in large scatter and usually do not provide satisfactory predictions. The objective of this paper is to determine trends in drift capacities of modern URM walls from 61 experimental tests and to investigate whether analytical models could lead to more reliable estimates of the displacement capacity than the currently used empirical models. A recently developed analytical model for the prediction of the ultimate drift capacity for both shear and flexure controlled URM walls is introduced and simplified into an equation that is suitable for code implementation. The approach follows the idea of plastic hinge models for reinforced concrete or steel structures. It explicitly considers the influence of crushing due to flexural or shear failure in URM walls and takes into account the effect of kinematic and static boundary conditions on the drift capacity. Finally, the performance of the analytical model is benchmarked against the test data and other empirical formulations. It shows that it yields significantly better estimates than empirical models in current codes. The paper concludes with an investigation of the sensitivity of the ultimate drift capacity to the wall geometry, static, and kinematic boundary conditions.  相似文献   

C-RESPONSE OF GEOMAGNETIC DEPTH SOUNDING ON A 1D THIN SHELL MODEL     

LI Shi-wen  WENG Ai-hua  TANG Yu  ZHANG Yan-hui  LI Jian-ping  YANG Yue 《地震地质》2018,40(2):337-348

This paper tries to formulate the C-response of geomagnetic depth sounding(GDS)on an Earth model with finite electrical conductivity. The computation is performed in a spherical coordinate system. The Earth is divided into a series of thin spherical shells. The source is approximated by a single spherical harmonic P₁⁰ due to the spatial structure of electrical currents in the magnetosphere. The whole solution space is separated into inner and external parts by the Earth surface. Omitting displacement current, the magnetic field in the external space obeys Laplacian equation, while in the inner part, due to the finite conductivity, the electromagnetic fields obey Helmholtz equation. To connect the magnetic fields in the inner and external space, the continuity condition of magnetic fields is used on the Earth surface. The external magnetic fields are expressed by the inner and external source coefficients, from which a new parameter called C-response is computed from the inner coefficient divided by the external coefficient, thus normalizing the actual source strength. The inner magnetic fields in each layer can be recursively derived by the continuity boundary condition of both normal and tangential components of the magnetic field from the initial boundary condition at core-mantle-boundary. The consistency of our C-responses with that from a typical 1-D global model validates the accuracy of the proposed algorithm. Numerical results also show that the C-response estimated from the geomagnetic transfer function method will deviate exceeding 5%from the actual response at longer periods than about 10⁶s, which means that ignoring the curvature of the Earth at extreme long periods will make inversion result unreliable. Therefore, an accurate C-response should be computed in order to lay a solid foundation for reliable inversion.  相似文献   

Time–space fractional governing equations of transient groundwater flow in confined aquifers: Numerical investigation          下载免费PDF全文

Tongbi Tu  Ali Ercan  M. Levent Kavvas 《水文研究》2018,32(10):1406-1419

In order to model non‐Fickian transport behaviour in groundwater aquifers, various forms of the time–space fractional advection–dispersion equation have been developed and used by several researchers in the last decade. The solute transport in groundwater aquifers in fractional time–space takes place by means of an underlying groundwater flow field. However, the governing equations for such groundwater flow in fractional time–space are yet to be developed in a comprehensive framework. In this study, a finite difference numerical scheme based on Caputo fractional derivative is proposed to investigate the properties of a newly developed time–space fractional governing equations of transient groundwater flow in confined aquifers in terms of the time–space fractional mass conservation equation and the time–space fractional water flux equation. Here, we apply these time–space fractional governing equations numerically to transient groundwater flow in a confined aquifer for different boundary conditions to explore their behaviour in modelling groundwater flow in fractional time–space. The numerical results demonstrate that the proposed time–space fractional governing equation for groundwater flow in confined aquifers may provide a new perspective on modelling groundwater flow and on interpreting the dynamics of groundwater level fluctuations. Additionally, the numerical results may imply that the newly derived fractional groundwater governing equation may help explain the observed heavy‐tailed solute transport behaviour in groundwater flow by incorporating nonlocal or long‐range dependence of the underlying groundwater flow field.  相似文献   

填充墙刚度影响的实测高层建筑增量动力分析          下载免费PDF全文

周云  裴熠麟  周祎  方亮  易伟建 《地震工程学报》2018,40(5):883-890

高层结构中的填充墙在地震作用下与周围结构构件之间的相互作用十分复杂,对建筑结构的整体抗震性能具有较大影响。然而我国规范在设计阶段通常不考虑填充墙对结构抗震性能的影响,统一采用周期折减系数来考虑其刚度变化引起的内力变化,因此准确评估填充墙对结构抗震性能的影响具有重要意义。本文在对一栋框-剪结构和一栋剪力墙高层建筑进行随机振动测试的基础上,利用Perform-3D对每栋高层分别建立了3种分析模型。其中对未考虑填充墙作用的结构模型,分别采取规范建议值和实测结果值两种方式进行周期折减。对通过添加斜撑单元来考虑填充墙作用的结构模型,利用环境激励测试识别获得的结构模态信息进行模型修正。对该3种模型进行了增量动力分析,探讨潜在危险性水平地震作用下填充墙对高层建筑抗震性能的影响。结果表明,填充墙增加了结构在弹性阶段的整体初始刚度,但随着地震动强度的增加逐渐丧失对结构刚度的贡献作用。相比考虑了填充墙作用的模型计算结果,规范建议的周期折减系数较为保守。同时研究发现,填充墙对高层框-剪结构的影响程度要比剪力墙结构大。  相似文献   

Analytic wave series solution of out-of-plane(SH) waves diffraction by an almost semi-circular shallow cylindrical hill          下载免费PDF全文

Chunyang Ji  Vincent Lee 《地震科学（英文版）》2018,31(3):154-165

A closed-form wave equation analytic solution of two-dimensional scattering and diffraction of outof-plane(SH) waves by an almost semi-circular shallow cylindrical hill on a flat, elastic and homogeneous half space is proposed by applying the discrete Fourier series expansions of sine and cosine functions. The semi-circular hill problem is discussed as a special case for the new formulated equation.Compared with the previous semi-circular cases solutions, the present method can give surface displacement amplitudes which agrees well with previous results. Although the proposed equation can only solve the problem of SH-waves diffracted by almost semi-circular shallow hills, the stress and displacement residual amplitudes are numerical insignificantly everywhere. Moreover, the influences of the depth-towidth ratio(a parameter defined in this paper to evaluate the shallowness of the topography of hills) on ground motions are presented and summarized. The limitations and errors of truncation from Graf's addition theorem and Fourier series equations in the present paper are also discussed.  相似文献   

华南陆缘高热流区的壳幔温度结构与动力学背景          下载免费PDF全文

张健  王蓓羽  唐显春  董淼  艾依飞 《地球物理学报》2018,61(10):3917-3932

华南陆缘是我国重要的矿产、地热资源区.晚中生代以来，在太平洋板块西向俯冲，地幔热对流活动共同作用下，该区出现多期岩浆-热事件和大规模爆发式成矿作用.在前人研究基础上，本文利用地表热流观测资料、地震剪切波资料、重力位球谐系数，计算了壳-幔温度结构，分析了动力学背景.计算结果表明：华南陆缘东南沿海地带，地壳10 km以浅温度达200℃以上，居里点温度475℃，莫霍面平均温度550℃.地壳浅层较热，花岗岩中放射性元素衰变放热是地壳浅层地下水热活动的重要热源，但地壳总体温度不高，为"冷壳热幔"型热结构.地幔中，90 km深度，温度950~1250℃；120 km深度，温度1050~1400℃；150 km深度，温度1200~1450℃；220 km深度，温度1500~1700℃."热"岩石圈底界深度在110~150 km之间，西深东浅.岩石圈内，地幔应力场为挤压-伸展相间格局；岩石圈之下，地幔应力场为一个以南昌为中心、长轴NE-SW向的椭圆.分析认为，晚中生代以来，太平洋板块的西向俯冲，导致华南陆缘在区域性SE向地幔对流背景上叠加局域性不稳定热扰动，在175~85Ma期间，上地幔物质向上流动，形成不同的岩浆活动高峰期.同时，岩石圈地幔受俯冲洋壳流体的影响，含水量高，黏度小，在地幔流切向应力场作用下，岩石圈底界由西向东"波浪"状减薄.现今岩石圈之下仍具备地幔小尺度热对流温度条件，但除地表浅层外，地壳整体温度不高，岩石圈构造稳定.  相似文献   

历史大地震断层滑动模型的建立及其对同震数值计算的影响——以1920年宁夏海原M_S8.5大地震为例          下载免费PDF全文

邓园浩  程惠红  张贝  张怀  石耀霖 《地球物理学报》2018,61(3):975-987

大地震的发生会引起区域位移场和应力场发生变化，进而改变区域内及临近断层的应力状态和地震活动性.目前，研究学者可据已有的断层滑动模型来计算分析大地震同震应力变化，同时采用库仑应力触发理论来进一步分析震后余震分布和断层危险性.然而，历史上曾经发生过不少大地震，例如，1920年的海原M_S8.5大地震，是全球范围内少见的特大地震之一.局限于无确切的地震台站地震波等资料，前人在研究历史地震的影响时往往给出一些简单的断层滑动模型，将断层面上错动量视为均匀分布.为更准确地了解历史地震对后续地震的影响，基于前人研究和一般地震滑动形态分布规律及地震反射剖面等资料，以海原M_S8.5大地震为例，探讨了如何建立海原大地震断层滑动模型，并分别搭建了简单断层滑动模型和复杂断层滑动模型的全球同震横向不均匀并行椭球型地球模型.通过对海原M_S8.5地震的同震位移场和应力场的计算，发现采用复杂断层滑动模型比简单断层滑动模型地表位错分布更切合实际.同时，进一步计算和分析了此次大地震对青藏高原东北缘近100年历史地震和周围断层的应力触发作用，得出断层滑动模型对同震计算结果的影响集中在发震断层附近而对远场影响较小.  相似文献   

Conditional effects of tides and waves on short‐term marsh sedimentation dynamics          下载免费PDF全文

Zhigang Ma  Tom Ysebaert  Daphne van der Wal  Peter M.J. Herman 《地球表面变化过程与地形》2018,43(10):2243-2255

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3D P-WAVE VELOCITY STRUCTURE AT THE NORTHEASTERN MARGIN OF ORDOS BLOCK     

HAN Xiao-ming  Liu Fang  ZHANG Fan  CHEN Li-feng  LI Juan  LI Shuan-hu  YANG Hong-ying 《地震地质》2018,40(1):215-231

Using the 7 100 absolute first arrivals of P waves and 91 513 relative P arrival times of 726 events at the northeastern margin of the Ordos block since 2009, the 3D fine structure of P wave velocity within the depth of 15km in the crust was inverted by the double difference seismic tomography method. The results show that there exist obvious high-speed continuous bodies in the northwest of the study area, and their lateral areas increase gradually with depth, while the velocity of east and south is relatively low. The velocity inhomogeneity exists and differs at different depths. The lateral differences of velocity are related to seismicity and faults. The 5~15km depth profile shows that earthquakes tend to occur in the area with relatively high velocity or high speed transition zones, which to some extent reflects the fragility of regional crustal media and the strong differential movement of faults in vertical and horizontal directions where the crust body is easy to absorb and store strain energy and generate major earthquakes. A "Y"-shape low-velocity channel is present in the lower crust around Liangcheng, corresponding to the NW-trending Heilaoyao-Shahukou fault set, which may reveal the migration path of the Late Tertiary-Quaternary basalt eruption. The Helingeer M6.2 earthquake in 1976 was related to the formation of the locking section of the thermal welding in this area. The three-dimensional fine structure of P wave velocity presented in this paper provides intuitive seismological evidence for physical and chemical properties of crustal media and the deep tectonic environment of earthquake preparation.  相似文献