Early diagenetic deformation structures of the Furongian ribbon rocks in Shandong Province of China——A new perspective of the genesis of limestone conglomerates

Ribbon rocks are characterized by an alternation of millimeter-to centimeter-thick limestone and argillaceous deposits (marlstone or shale).The sedimentary processes and diagenetic characteristics of ribbon rocks might be critical to the formation of limestone conglomerates.According to detailed field measurement and laboratory analyses (thin section observation and XRD analysis),four types of ribbon rocks are classified,i.e.,limestone and marlstone couplet (L-M),limestone and shale couplet (L-S),thin-bedde...     

Numerical modelling of morphodynamics—Vilaine Estuary

The main objective of this paper is to develop a method to simulate long-term morphodynamics of estuaries dominated by fine sediments, which are subject to both tidal flow and meteorologically induced variations in freshwater run-off and wave conditions. The method is tested on the Vilaine Estuary located in South Brittany, France. The estuary is subject to a meso–macrotidal regime. The semi-diurnal tidal range varies from around 2.5 to 5 m at neap and spring, respectively. The freshwater input is controlled by a dam located approximately 8 km from the mouth of the estuary. Sediments are characterised as mostly fines, but more sandy areas are also found. The morphology of the estuary is highly influenced by the dam. It is very dynamic and changes in a complicated manner with the run-off from the dam, the tide and the wave forcing at the mouth of the estuary. Extensive hydrodynamic and sediment field data have been collected in the past and provide a solid scientific basis for studying the estuary. Based on a conceptual understanding of the morphodynamics, a numerical morphological model with coupled hydrodynamic, surface wave and sediment transport models is formulated. The numerical models are calibrated to reproduce sediment concentrations, tidal flat altimetry and overall sediment fluxes. Scaling factors are applied to a reference year to form quasi-realistic hydrodynamic forcing and river run-off, which allow for the simulations to be extended to other years. The simulation results are compared with observed bathymetric changes in the estuary during the period 1998–2005. The models and scaling factors are applied to predict the morphological development over a time scale of up to 10 years. The influence of the initial conditions and the sequence of external hydrodynamic forcing, with respect to the morphodynamic response of the estuary, are discussed.     

Patterns of seismic sequences in the Levant—interpretation of historical seismicity

There are historical accounts of about a hundred damaging earthquakes that occurred during the last two millennia in the Levant, in and around the Dead Sea fault system, and about half of which were associated with additional felt shocks. Several modes of earthquake sequences can be distinguished in them: (a) In 46 accounts, only one single event is noted. These are not known from tectonic settings similar to that of the Levant, and may just be a result of incomplete reporting. (b) In four cases, quakes preceded the mainshock by minutes, hours, and up to several weeks—possibly foreshocks. (c) Thirty-five mainshock–aftershock sequences were noted, lasting hours, days, weeks, months, and even more than a year; four of these also have foreshocks. No typical delay time was recognized for the largest or most significant aftershocks: they appeared up to several months later. (d) Six of the reported mainshock–aftershock sequences appeared in a “storm.” Another 13 sequences are insufficient to specify further.     

Experimental investigation of the elastic modulus of a fractal system—A model of fractured rocks

The elastic properties of a physical model representing a damaged rock matrix were studied using a square lattice deformed under tensile stress. The elastic modulusM of such a system varies in agreement with percolation theory as|x–x _c | ^f , wherex is the damage parameter andx _c the threshold value of the damage parameter,f3.6. Atxx _c the scale dependence ofM can be expressed asML ^–f/v , whereL is the size of the sample andv the correlation exponent in percolation theory.The experimental results are of interest in assessing elastic properties in earthquake focal zones and fault zones in general.     

Geology of the Grove Mountains in East Antarctica——New evidence for the final suture of Gondwana Land

As the core block of the East Gondwana Land, the East Antarctic Shield was traditionally thought, before 1992, as an amalgamation of a number of Archaean-Paleoproterozoic nuclei, be-ing welded by Grenville aged mobile belts during 1400—900 Ma, while the …     

Role of reservoirs in sustained seismicity of Koyna-Warna region—a statistical analysis

Koyna-Warna region in western India is a globally recognized site of reservoir-triggered seismicity near the Koyna and Warna reservoirs. The region has been reported with several M?>?5 earthquakes in the last five decades including M6.3 Koyna earthquake which is considered as the largest triggered earthquake worldwide. In the present study, a detailed statistical analysis has been done for long period earthquake catalogues during 1968–2004 of MERI and 2005–2012 of CSIR-NGRI to find out the spatio-temporal influence of the Koyna and Warna reservoirs impoundment on the seismicity of the region. Depending upon the earthquake clusters, we divided the region into three different zones and performed power spectrum and singular spectrum analysis (SSA) on them. For the time period 1983–1995, the earthquake zone near the Warna reservoir; for 1996–2004, the earthquake zone near the Koyna reservoir; and for 2005–2012, the earthquake zone near the Warna reservoir found to be influenced by the annual water level variations in the reservoirs that confirm the continuous role of both the reservoirs in the seismicity of the Koyna-Warna region.     

Major element chemistry of ocean island basalts — Conditions of mantle melting and heterogeneity of mantle source

We estimate average compositions of near-primary, ‘reference’ ocean island basalts (OIBs) for 120 volcanic centers from 31 major island groups and constrain the depth of lithosphere–asthenosphere boundary (LAB) at the time of volcanism and the possible depth of melt–mantle equilibration based on recently calibrated melt silica activity barometer. The LAB depth versus fractionation corrected OIB compositions (lava compositions, X, corrected to Mg# 73, X_OIB^#73, i.e., magmas in equilibrium with Fo₉₀, if olivine is present in the mantle source) show an increased major element compositional variability with increasing LAB depths. OIBs erupted on lithospheres < 40 km thick approach the compositions (e.g. SiO₂^#73, TiO₂^#73, [CaO/Al₂O₃]^#73) of primitive ridge basalts and are influenced strongly by depth and extent of shallow melting. However, X_OIB^#73 on thicker lithospheres cannot be explained by melt–mantle equilibration as shallow as LAB. Melt generation from a somewhat deeper (up to 50 km deeper than the LAB) peridotite source can explain the OIB major element chemistry on lithospheres ≤ 70 km. However, deeper melting of volatile-free, fertile peridotite is not sufficient to explain the end member primary OIBs on ≥ 70 km thick lithospheres. Comparison between X_OIB^#73 and experimental partial melts of fertile peridotite indicates that at least two additional melt components need to be derived from OIB source regions. The first component, similar to that identified in HIMU lavas, is characterized by low SiO₂^#73, Al₂O₃^#73, [Na₂O/TiO₂]^#73, and high FeO?^#73, CaO^#73, [CaO/Al₂O₃]^#73. The second component, similar to that found in Hawaiian Koolau lavas, is characterized by high SiO₂^#73, moderately high FeO?^#73, and low CaO^#73 and Al₂O₃^#73. These two components are not evenly sampled by all the islands, suggesting a heterogeneous distribution of mantle components that generate them. We suggest that carbonated eclogite and volatile-free, silica-excess eclogite are the two most likely candidates, which in conjunction with fertile mantle peridotite, give rise to the two primitive OIB end members.     

Scattering and diffraction of earthquake motions in irregular,elastic layers,II: Rayleigh and body P and SV waves

We present our study of the wave propagation in an irregularly layered, elastic wave-guide excited by incoming Rayleigh surface waves and P and SV body waves. Our aim is to show examples of applying a method that will make it possible to analyze the distribution and amplification of displacements, rotations, curvatures, strains, and stresses on or below the ground surface during passage of strong earthquake ground motion. We employ the weighted-residuals method, which makes it possible to calculate the scattered and diffracted waves, and then we illustrate the amplification of motions in the vicinity of inhomogeneity.     

SV波斜入射下混凝土重力坝易损性分析

易损性分析是评估不同强度地震作用下混凝土重力坝各级破坏概率的有效方法。目前重力坝易损性分析通常假定地震波为垂直入射,然而在近断层区域,地震波往往是倾斜入射的,地震波斜入射对重力坝地震响应有显著影响。从太平洋地震工程研究中心数据库选取16条地震动记录,采用黏弹性人工边界结合等效节点荷载实现SV波斜入射波动输入。采用增量动力分析方法对地震动峰值加速度进行调幅,以印度Koyna混凝土重力坝为研究对象,以坝顶相对位移为抗震性能指标,建立SV波斜入射下重力坝不同震损等级的易损性曲线。结果表明,与垂直入射相比,相同震损等级和相同地震动强度下,斜入射时重力坝破坏概率减小;当PGA接近重力坝实际遭受的地震动强度时,入射角为15°和30°时破坏概率与垂直入射相比最大减小率分别为27.3%和68.2%;各地震强度下,15°和30°斜入射相对于垂直入射的破坏概率差异值最大分别达36.6%、83.9%。因此,混凝土重力坝抗震性能分析应考虑地震波斜入射的影响。研究结果也可为近断层区域混凝土重力坝安全风险评估提供参考。     

Peak earthquake response of structures under multi-component excitations

Accurate estimation of the peak seismic responses of structures is important in earthquake resistant design. The internal force distributions and the seismic responses of structures are quite complex, since ground motions are multi- directional. One key issue is the uncertainty of the incident angle between the directions of ground motion and the reference axes of the structure. Different assumed seismic incidences can result in different peak values within the scope of design spectrum analysis for a given structure and earthquake ground motion record combination. Using time history analysis to determine the maximum structural responses excited by a given earthquake record requires repetitive calculations to determine the critical incident angle. This paper presents a transformation approach for relatively accurate and rapid determination of the maximum peak responses of a linear structure subjected to three-dimensional excitations within all possible seismic incident angles. The responses can be deformations, internal forces, strains and so on. An irregular building structure model is established using SAP2000 program. Several typical earthquake records and an artifi cial white noise are applied to the structure model to illustrate the variation of the maximum structural responses for different incident angles. Numerical results show that for many structural parameters, the variation can be greater than 100%. This method can be directly applied to time history analysis of structures using existing computer software to determine the peak responses without carrying out the analyses for all possible incident angles. It can also be used to verify and/or modify aseismic designs by using response spectrum analysis.     

不同倾角断层对场地动力放大效应的分析

一般认为断层有一定的隔震作用,但是也有不少震害表明断层附近的破坏反而比较严重。为探讨其中机理,采用有限元方法分别建立包含不同倾角无厚度断层的场地模型,并分析了在各种频率入射波的作用下该场地的动力反应。计算结果表明,断层对场地的动力反应有一定的放大作用,特别是当入射波的频率与场地的基频接近时,放大效应更为明显。计算结果还表明,断层的倾角对场地的动力反应也有影响,随着断层倾角的减小,断层出露点附近的动力放大效应增大。     

SV波全反射作用下地震动的合成及振动特性

越来越多的研究表明来自基岩的地震波并不是垂直地面向上传播的。地震波在斜入射与垂直入射时所产生的场地效应有很大不同,由于存在全反射现象,SV波在斜入射时产生的场地效应更为复杂。文章基于均匀弹性半空间地震波传播理论,分别推导得到SV波入射角在小于、大于等于临界角时地震动的计算表达式,通过模型算例研究SV波全反射作用下的地震动特性。研究发现：由SV波产生的地震动主要由入射波和反射波构成,滑行波作用可以忽略;地面运动轨迹具有面波旋转振动特点;随着入射角的增大,地面震动从以水平方向振动为主逐渐过渡到以垂直方向振动为主,两个方向的振动均小于入射波峰值的2倍。     

Impact of incident angles of P waves on the dynamic responses of long lined tunnels

The impact of the incident angle of earthquake motion on the seismic response of the long lined tunnels is studied. Based on the time‐domain finite element method with the viscous‐spring artificial boundary condition, the earthquake motion of oblique incidence is transformed into the equivalent nodal forces acting on the truncated boundary of finite element model. In the present work, the formulas of equivalent nodal forces for the plane P wave with arbitrary incident angle are deduced and implemented into the commercial software abaqus   1 . The effectiveness of the formulas and its implementation are demonstrated by two numerical examples with the reference solutions. The proposed method is applied to investigate the seismic responses of the long lined tunnels under the obliquely incident P waves. The numerical results indicate that the seismic responses of the long lined tunnels are highly affected by the incident angles of P waves. Copyright © 2016 John Wiley & Sons, Ltd.     

On the Ultra Long Propagation of Felt Ground Motion Due to the <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">w</Emphasis></Subscript> 8.3 Deep-Focus Sea-of-Okhotsk Earthquake of May 24, 2013

This study uses macroseismic data and wave equations to solve the problem of ultra long propagation of felt ground motion (over 9000 km from the epicenter) due to the Sea-of-Okhotsk earthquake. We show that the principal mechanism of this phenomenon could be excitation of a previously unknown standing radial wave as a mode of the Earth’s free oscillations, ₀S₀, due to the superposition of an incident and a reflected spherical P wave in the epicentral area of the Sea-of-Okhotsk earthquake. The standing wave generates slowly attenuating P waves that travel over the earth’s surface that act as carrying waves; when superposed on these, direct body waves acquire the ability to travel over great distances. We show previously unknown parameters of the radial mode ₀S₀ for the initial phase of earth deformation due to the large deep-focus earthquake. We used data on the Sea-of-Okhotsk and Bolivian earthquakes to show that large deep-focus earthquakes can excite free oscillations of the Earth that are not only recorded by instrumental means, but are also felt by people, with the amplification of the macroseismic effect being directly related to the phenomenon of resonance for multistory buildings.     

Antiplane response of isoceles triangular hill to incident SH waves

In this paper, antiplane response of an isosceles triangular hill to incident SH waves is studied based on the method of complex function and by using moving coordinate system. The standing wave function, which can satisfy the governing equation and boundary condition, is provided. Furthermore, numerical examples are presented; the influences of wave number and angle of the incident waves and the angle of the hill's peak on ground motion are discussed.     

一种利用单台强震记录计算任意场地三分量地面运动的方法

本文利用近场理论格林函数反褶积的方法计算土层的地震反应.解答中包含了产生地面运动的各种反射、透射和转换波震相,也计入了土层与基底介质的相互作用.将计算的土层响应与已获得的近场加速度记录褶积,可算出不同土层场地上垂直向和水平向三分量的地面运动.文中利用1982年卢龙地震的近场加速度记录,检验了方法的可行性.     

一种利用单台强震记录计算任意场地三分量地面运动的方法

本文利用近场理论格林函数反褶积的方法计算土层的地震反应.解答中包含了产生地面运动的各种反射、透射和转换波震相,也计入了土层与基底介质的相互作用.将计算的土层响应与已获得的近场加速度记录褶积,可算出不同土层场地上垂直向和水平向三分量的地面运动.文中利用1982年卢龙地震的近场加速度记录,检验了方法的可行性.