Analytical study of ground motion caused by seismic wave propagation across faulted rock masses          下载免费PDF全文

J.C. Li  N.N. Li  S.B. Chai  H.B. Li 《国际地质力学数值与分析法杂志》2018,42(1):95-109

Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Q_p and Q_s. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions.  相似文献   

Genetic variability of the Lessepsian migrant mussel Brachidontes pharaonis (Bivalvia: Mytilidae) in Tunisia     

M Antit  J Urra  AN Alagaili  S Farjallah 《African Journal of Marine Science》2018,40(2):211-217

The present study used two mitochondrial markers (16S rRNA and COI) to assess the genetic diversity of a newly founded Lessepsian migrant mussel, Brachidontes pharaonis, in Tunisian waters. The species appears to be restricted to only one population in Rades Harbour, in the northern part of the country. Phylogenetic analyses revealed the monophyly of B. pharaonis in Tunisia. Both molecular markers revealed high genetic variability of the B. pharaonis population. Haplotype networks and demographic analyses confirmed the recent expansion events within this population. Multiple human-mediated introduction events involving several founder populations and intensive population growth rates are probably the main causes of the high polymorphism observed within this invasive mollusc.  相似文献   

Geography Deserts: State and Regional Variation in the Formal Opportunity to Learn Geography in the United States, 2005–2015     

Mark C. Jones  Marcos Luna 《The Journal of geography》2019,118(2):88-100

The formal opportunity to learn geography in the United States is unevenly distributed across space, creating possible geography deserts. Data on the number of exams taken in Advanced Placement Human Geography (APHG) and bachelor’s degrees earned in geography are mapped at the state and regional scales. Normalized rates are ranked and grouped into quintiles. For APHG exams, states in the southeastern region of the United States are in the uppermost quintiles while states in the northeastern region are in the lowermost quintiles. The pattern for bachelor’s degrees in geography is somewhat the spatial inverse of that for APHG.  相似文献   

Comprehensive Geological–Geophysical and Botanic Study of the Tectonic Junction Zone between the Katun Ridge and Uimon Depression (Altai Mountains)     

Boyarskikh  I. G.  Agatova  A. R.  Kulikova  A. I.  Bakiyanov  A. I.  Skaptsov  M. V.  Mazeika  J. 《Izvestiya Atmospheric and Oceanic Physics》2018,54(8):805-825

Izvestiya, Atmospheric and Oceanic Physics - Areas with large gradients and anomalous variations in geomagnetic and radiation fields have been revealed and mapped at the northwestern foot of the...  相似文献   

Geophysical Signature of the Shallow Water Flow in the Deepwater Basin of the Northern South China Sea     

Xiaohua Zhang  Yunbao Sun  Shiguo Wu 《中国海洋大学学报(英文版)》2018,17(4):791-798

Shallow water flow (SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea (SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson’s ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS.  相似文献   

Nonlinear model to study filamentation instability of circularly polarized dispersive Alfvén waves in solar wind plasmas     

Swati Sharma  R. P. Sharma  M. K. Mishra 《Astrophysics and Space Science》2018,363(8):164

This paper examines the small-scale solar wind turbulence driven in view of the Alfvén waves subjected to ponderomotive nonlinearity. Filamentation instability is known to take place for the case of dispersive Alfvén wave (DAW) propagating parallel to the ambient magnetic field. The ponderomotive force associated with DAW is responsible for wave localization and these webs of filaments become more intense and irregular as one proceeds along the spatial domain. The ponderomotive force associated with pump changes with pump parameters giving rise to different evolution patterns. This paper studies in detail the nonlinear evolution of filamentation instability introduced by dispersive Alfven waves (DAWs) which becomes dispersive on account of the finite frequency of DAW i.e., pump frequency is comparable to the ion cyclotron frequency. We have explicitly obtained the perturbation dynamics and then examined the impact of pump magnitude on the driven magnetic turbulence using numerical simulation. The results show steepening at small scales with increasing pump amplitude. The compressibility associated with acoustic fluctuations may explain the variation in spectral scaling of solar wind turbulence as observed by Alexandrova et al. (Astrophys. J. 674:1157, 2008).  相似文献   

Petrochronology of oxidized granulites from southern Peru     

Chris Yakymchuk  Adrian Rehm  Zhuoheng Liao  John M. Cottle 《Journal of Metamorphic Geology》2019,37(6):839-862

Sapphirine–quartz granulites from the Cocachacra region of the Arequipa Massif in southern Peru record early Neoproterozoic ultrahigh‐temperature metamorphism. Phase equilibrium modelling and zircon petrochronology are used to quantify timing and pressure–temperature (P–T) conditions of metamorphism. Modelling of three magnetite‐bearing sapphirine–quartz samples indicates peak temperatures of >950°C at ~0.7 GPa and a clockwise P–T evolution. Elevated concentrations of Al in orthopyroxene are also consistent with ultrahigh‐temperature conditions. Neoblastic zircon records ages of c. 1.0–0.9 Ga that are interpreted to record protracted ultrahigh‐temperature metamorphism. Th/U ratios of zircon of up to 100 reflect U‐depleted whole‐rock compositions. Concentrations of heavy rare earth elements in zircon do not show systematic trends with U–Pb age but do correlate with variable whole‐rock compositions. Very large positive Ce anomalies in zircon from two samples probably relate to strongly oxidizing conditions during neoblastic zircon crystallization. Low concentrations of Ti‐in‐zircon (<10 ppm) are interpreted to result from reduced titania activities due to the strongly oxidized nature of the granulites and the sequestration of titanium‐rich minerals away from the reaction volume. Whole‐rock compositions and oxidation state have a strong influence on the trace element composition of metamorphic zircon, which has implications for interpreting the geological significance of ages retrieved from zircon in oxidized metamorphic rocks.  相似文献   

The most primitive mesosiderite Northwest Africa 1878, subgroup 0     

M. Kimura  N. Sugiura  A. Yamaguchi  K. Ichimura 《Meteoritics & planetary science》2020,55(5):1116-1127

All mesosiderites previously reported were subjected to thermal metamorphism and/or partial melting on the parent body. Therefore, their primordial features have been mostly lost. Here, we report detailed petrological and mineralogical features on a mesosiderite, Northwest Africa (NWA) 1878. This meteorite comprises silicate lithology and aggregates of small spheroidal Fe‐Ni metal grains. Silicate lithology typically shows igneous texture without recrystallization features, and mainly consists of low‐Ca pyroxene and plagioclase. Pyroxenes often show normal zoning. Exsolution lamella of augite is rarely noticed and very thin in width, compared with other mesosiderites. A few magnesian olivine grains are encountered without typical corona texture around them. They are not equilibrated with pyroxene on a large scale. Plagioclase shows a wide compositional range. These results show that NWA 1878 hardly experienced thermal metamorphism, distinguished from mesosiderites of subgroups 1–4. Therefore, we propose that this is classified as subgroup 0 mesosiderite. Nevertheless, NWA 1878 was locally subjected to secondary reactions, such as weak reduction of pyroxene and Fe‐Mg diffusion between olivine and pyroxene, on the parent body.  相似文献   

Factors influencing biodeposit production by the New Zealand freshwater mussel Echyridella menziesii     

Kevin J. Collier  Susan J. Clearwater  Paula H. M. W. Neijenhuis  Susanna A. Wood 《新西兰海洋与淡水研究杂志》2018,52(1):1-15

Laboratory experiments on the New Zealand freshwater mussel Echyridella menziesii were used to investigate the short-term effects (7–8 days) of food type on rates of biodeposition and benthic substrate respiration. Post-feeding biodeposition rates ranged from 0.34 to 1.52?mg?g^?1?h^?1 (mean?=?0.50?mg g^?1?h^?1) and were unaffected by the addition of toxin-producing Microcystis. Addition of suspended sediment (30?mg?L^?1) visibly altered substrate composition, and increased total and inorganic biodeposit production rates by 24–33% compared to mussels fed commercial phytoplankton stock. Biodeposition rates of mussels in lake bed substrates were 38% higher than those in silica sand for identical feeding regimes, suggesting that a significant proportion of material produced in this experiment could have been derived from feeding on organic matter in the lake bed sediments. Respiration rates were higher in treatments with Microcystis but were unaffected by the presence of mussels. This laboratory study suggests that biodeposition by E. menziesii is resilient to short-term exposure to Microcystis, and highlights the ability of mussels to alter benthic substrate composition by incorporating suspended sediment into substrates.  相似文献   

Numerical Simulation of the Vortex-Induced Vibration of A Curved Flexible Riser in Shear Flow     

Hong-jun Zhu  Peng-zhi Lin 《中国海洋工程》2018,32(3):301-311

A series of fully three-dimensional(3 D) numerical simulations of flow past a free-to-oscillate curved flexible riser in shear flow were conducted at Reynolds number of 185–1015. The numerical results obtained by the two-way fluid–structure interaction(FSI) simulations are in good agreement with the experimental results reported in the earlier study. It is further found that the frequency transition is out of phase not only in the inline(IL) and crossflow(CF) directions but also along the span direction. The mode competition leads to the non-zero nodes of the rootmean-square(RMS) amplitude and the relatively chaotic trajectories. The fluid–structure interaction is to some extent reflected by the transverse velocity of the ambient fluid, which reaches the maximum value when the riser reaches the equilibrium position. Moreover, the local maximum transverse velocities occur at the peak CF amplitudes, and the values are relatively large when the vibration is in the resonance regions. The 3 D vortex columns are shed nearly parallel to the axis of the curved flexible riser. As the local Reynolds number increases from 0 at the bottom of the riser to the maximum value at the top, the wake undergoes a transition from a two-dimensional structure to a 3 D one. More irregular small-scale vortices appeared at the wake region of the riser, undergoing large amplitude responses.  相似文献