瑞雷波检测技术在强夯块石地基中的应用

基于瑞雷波测试原理及测试方法,主要研究了瑞雷波检测结果在含块石人工填土强夯地基处理中的应用.瑞雷波检测数据不仅可以对场地均匀性及有效加固深度进行评价,采这数据,结合其它检测手段,还可以确定强夯地基的变形模量、地基承载力、地基沉降量等地基参数,具有现实的工程指导意义.     

Lithospheric structure beneath the East China Sea revealed by Rayleigh-wave phase velocities

We explore the variations of Rayleigh-wave phase-velocity beneath the East China Sea in a broad period range (5–200 s). Rayleigh-wave dispersion curves are measured by the two-station technique for a total of 373 interstation paths using vertical-component broad-band waveforms at 32 seismic stations around the East China Sea from 6891 global earthquakes.The resulting maps of Rayleigh-wave phase velocity and azimuthal anisotropy provide a high resolution model of the lithospheric mantle beneath the East China Sea. The model exhibits four regions with different isotropic and anisotropic patterns: the Bohai Sea, belonging to the North China Craton, displays a continental signature with fast velocities at short periods; the Yellow Sea, very stable unit associated with low deformation, exhibits fast velocities and limited anisotropy; the southern part of the East China Sea, with high deformation and many fractures and faults, is related to slow velocities and high anisotropic signature; and the Ryukyu Trench shows high-velocity perturbations and slab parallel anisotropy.     

Emplacement of the La Peña alkaline igneous complex,Mendoza, Argentina (33° S): Implications for the early Miocene tectonic regime in the retroarc of the Andes

The La Peña alkaline complex (LPC) of Miocene age (18–19 Ma) lies on the eastern front of the Precordillera (32°41ʹ34ʺS, 68°59ʹ48″W, 1400–2900 m a.s.l.), 30 km northwest of Mendoza city, Argentina. It is a subcircular massif of 19 km² and 5 km in diameter, intruded in the metasedimentary sequence of the Villavicencio Formation of Silurian-Devonian age. It is the result of integration of multiple pulses derived from one or more deep magma chambers, which form a suite of silicate rocks grouped into: a clinopyroxenite body, a central syenite facies with a large breccia zone at the contact with the clinopyroxenite, bodies of malignite, trachyte and syenite porphyry necks, and a system of radial and annular dikes of different compositions. Its subcircular geometry and dike system distribution are frequent features of intraplate plutons or plutons emplaced in post-orogenic settings. These morphostructural features characterize numerous alkaline complexes worldwide and denote the importance of magmatic pressures that cause doming with radial and annular fracturing, in a brittle country rock. However, in the LPC, the attitude of the internal fabric of plutonic and subvolcanic units and the preferential layout of dikes match the NW–SE extensional fractures widely distributed in the host rock. This feature indicates a strong tectonic control linked to the structure that facilitate space for emplacement, corresponding to the brittle shear zone parallel to the N–S stratigraphy of the country rock. Shearing produced a system of discontinuities, with a K fractal fracture pattern, given by the combination of Riedel (R), anti-Riedel (R′), (P) and extensional (T) fracture systems, responsible for the control of melt migration by the opening of various fracture branches, but particularly through the NW–SE (T) fractures. Five different pulses would have ascent, (1) an initial one from which cumulate clinopyroxenite was formed, (2) a phase of mafic composition represented by dikes cross-cutting the clinopyroxenite, (3) a malignite facies that causes a small breccia in the clinopyroxenite, (4) a central syenite facies that develops breccias at the contact with the clinopyroxenite and, finally, (5) porphyry necks and a system of radial dikes intruding all units. At the moment of the emplacement different mechanisms would have acted, they summarized in: 1) opening of discontinuities synchronous to the magma circulation as the principal mechanism for formation of dikes and conduits; 2) stoping processes, that play an important role in the development of the breccia zone and enabling an efficient transference of material during the emplacement of the syenitic magma and 3) shear-related deformation (regional stress), affected the internal fabric of the facies, causing intracrystalline deformation and submagmatic flow, which is very evident in the central syenite intrusive. The kinematic analysis of shear planes allows proposing that emplacement of the LPC took place in a transtensive regime, which would have occurred in the back-arc of the Andes orogen, during a long period spanning from Miocene to the present, of the compressive deformation responsible, westward and at the same latitude, for the development of the Aconcagua fold and thrust belt.     

The effect of Newtonian cooling on vertically propagating magneto-acoustic waves in a thermally conducting isothermal atmosphere (II)

In this article, we examine reflection, dissipation and attenuation of vertically propagating waves in an isothermal atmosphere under the combined effect of Newtonian cooling, thermal conduction and viscosity with a weak horizontal magnetic field. We consider the case in which the combined effect of viscosity and magnetic field is dominated by that of the thermal conduction and for small values of the Newtonian parameter. As a result, the atmosphere can be divided into three distinct regions that are connected by two transition regions. The lower and middle regions are connected by a semi-transparent barrier and the middle and upper regions are connected by an absorbing and reflecting barrier. In the connecting barriers the reflection and transmission of the waves takes place. The presence of Newtonian cooling effects on the adiabatic region, produces attenuation in the amplitudes of the waves and reduces the energy absorption in the transition regions. The reflection coefficient is determined in the lower and middle regions and the results are discussed in the context of the heating of the solar atmosphere.     

Shock surfing acceleration

Analytical and numerical analysis identify shock surfing acceleration as an ideal pre-energization mechanism for the slow pick-up ions at quasiperpendicular shocks. After gaining sufficient energy by shock surfing, pick-up ions undergo diffusive acceleration to reach their observed energies. Energetic ions upstream of the cometary bow shock, acceleration of solar energetic particles by magnetosonic waves in corona, ion enhancement in interplanetary shocks, generation of anomalous cosmic rays from interstellar pick-up ions at the termination shock are some of the cases where shock surfing acceleration apply. Inclusion of the lower-hybrid wave turbulence into the laminar model of shock surfing can explain the preferential acceleration of heavier particles as observed by Voyager at the termination shock. At relativistic energies, unlimited acceleration of ions is theoretically possible; because for sufficiently strong shocks main limitation of the mechanism, caused by the escape of accelerated particles downstream of the shock during acceleration no longer exists.     

Multiscale linearized inversion of surface-wave dispersion curves

In recent years, surface-wave analysis method has been developed rapidly in many fields. Multichannel analysis of surface waves can provide near-surface one-dimensional shear-wave velocity profiles. Because linearized inversion of surface-wave dispersion curves relies heavily on the choice of the initial model, setting an inappropriate initial model can lead to poor inversion results, or even failure of inversion. However, it is difficult to establish a reasonable initial model without a priori information, which is unavailable in most cases. To cope with this problem, a multiscale linearized inversion method is proposed for surface-wave dispersion curves inversion. In contrast with the traditional single-scale linearized inversion, the key idea of the proposed multiscale surface-wave inversion method is the introduction of a merging and splitting process of layers. After every scale inversion, the merging and splitting operations automatically optimize the inversion model, making it gradually approach to a reasonable subsurface stratification. Multiscale surface-wave inversion method reduces the difficulty of establishing the initial model and has high computational efficiency. In addition, it has strong ability to identify high-velocity or low-velocity interlayers and thin layers, especially suited for the geological conditions with obvious stratification. In synthetic tests, the proposed method was compared with the single-scale surface-wave inversion and particle swarm optimization algorithm to demonstrate the effectiveness and practicability of multiscale surface-wave inversion method. We also applied the multiscale surface-wave inversion method to field seismic data acquired in Guizhou, China and Texas, USA. Borehole and crosshole test data were compared with the inversion results of field data to prove the reliability of the proposed method.     

Influence of deformation bands on sandstone porosity: A case study using three-dimensional microtomography

This study presents a qualitative and quantitative analysis of porosity in deformation bands by applying X-ray micro-computed tomography in conjunction with microstructural analysis. Samples of compactional cataclastic bands and shear compactional bands identified in Early Cretaceous aeolian sandstones of the Paraná Basin were analyzed. The application of X-ray micro-computed tomography expanded the view of features in the porous framework of each type of deformation band studied and provided information that are not clear or was not observable with optical microscopy. The compactional cataclastic bands and shear compactional bands differ in geometry, thickness, microstructures and, mainly, in the distribution, shape and orientation of the remaining pores. Porosity analysis was also performed by comparing values of porosity (total, open and closed pores) of the parental rock and the deformation band in each sample. Results of these analyses show a reduction of total porosity and open pores and therefore an increase in the amount of closed pores in all types of deformation bands in relation to parental rock. In addition, it is observed that changes in porosity characteristics are related to the effect of different deformation mechanisms that operated in each type of deformation band.     

东川拖布卡金矿矿化层位与找金方向

超大型拖布卡金矿的发现,表明东川地区具备找金前景.“黑层”是金的成矿前提,断裂加蚀变是成矿必备条件,基性与中性岩脉在容矿层中的侵位,是找富金的重要标志.金成矿全过程应是多旋回（晋宁、华力西、燕山、喜马拉雅山）成矿作用,且受剪切破碎带控制的黑层型金矿.     

辽南北瓦沟长英质岩石应变组构演化

岩石的应变组构型式与岩石成分、变形环境和应变过程有着密切关系。北瓦沟地区低角闪岩相条作下的长英质岩石,表现脆性、韧性和韧脆性过渡,因而在剪切作用过程中形成了相应的应变组构型式,即脆性应变组构、韧性应变组构和脆-韧性应变组构。而且随着应变过程的发展,应变组构也表现出一定的演化规律。     

Sheathfolds in rheomorphic ignimbrites

Structural reappraisal of several classic rheomorphic ignimbrites in Colorado, Idaho, the Canary Islands and Italy has, for the first time, revealed abundant oblique folds, curvilinear folds and sheathfolds which formed during emplacement. Like their equivalents in tectonic shear-zones, the sheathfold axes lie sub-parallel to a pervasive elongation lineation, and appear as eye structures on rock surfaces normal to the transport direction. With the recognition of sheathfolds, ignimbrites previously inferred to have undergone complex rheomorphic deformation histories are re-interpreted as recording a single, progressive deformation event. In some examples, the trends of sheathfolds and related lineations change with height through a single ignimbrite suggesting that rheomorphism did not affect the entire thickness of ignimbrite synchronously. Instead, we infer that in these ignimbrites a thin ductile shear-zone rose gradually through the aggrading agglutinating mass whilst the flow direction varied with time. This suggests that, in some cases, both welding and rheomorphism can be extremely rapid, with ductile strain rates significantly exceeding rates of ignimbrite aggradation.Editorial responsibility: T. Druitt