A new regime of volcanic eruption due to the relative motion between liquid and gas

In explosive magma eruptions, magma ascends through a conduit as a Poiseuille flow at depth, and gas exsolves gradually and expands as the pressure decreases (bubbly flow regime). When the volume fraction of gas becomes sufficiently large, liquid or solid parts of magma fragment into droplets or ashes, and the flow dynamics becomes governed by the gas phase (gas–ash flow regime). We propose a new flow regime, which we call fractured-turbulent flow regime, between the bubbly flow regime and the gas–ash flow regime. In the new regime, both liquid magma and gas are continuous phases. The high connectivity of the two phases allows the relative velocity between them to increase significantly. We present one sample calculation, which displays basically explosive characteristics, but has three features distinct from previous models. The explosive characteristics are manifested as the fragmentation of the magma and the high speed jet that issues from the vent. The first distinct feature is a nearly lithostatic pressure distribution, which results from the increase of the height of the fragmentation surface. The second one is the atmospheric pressure at the vent; the flow is not choked. The third one is that the relative velocity between the gas and the ash is large at the vent despite the large interaction force between the two phases. The large relative velocity is established in the fractured-turbulent regime, and is maintained in the subsequent gas–ash flow regime.     

Pseudo relative velocity spectra of earthquake ground motion at long periods

This paper analyses the processes which govern structural response, and uses observations of strong earthquake ground motion to propose quantitative extrapolation of pseudo relative velocity spectral amplitudes to long (100 > T > 1 s) periods. This will eliminate the current difficulties with rough estimation of long period spectral amplitudes and will open new possibilities by enabling the strong motion hazard calculations to be extended to the same long period band. So far, the scaling equations of response spectrum amplitudes have been valid only up to periods less than several seconds. The design of long structures and of structures on multiple distant supports requires knowledge and specification of design ground motions well beyond 1–10 s periods. With the results presented in this paper it will be possible to compute site-specific uniform hazard spectra and associated synthetic accelograms for essentially all long period response problems.     

On one integral of equations of motion of relative horizontal flow

Резюме Бьул выведен интеграл уравнений двнженид Лагранжа, соответствующжа, соответствуюший чоступательниым, неустойчивым, тошоидальным волнам на границе раздела двух зональнух течений. Внд границы раздела в течение развития волны меняется, превращаясь из обычной трохоиды в циклоиду. Числовые оценки показывают, что рассматриваемые волны цхематичесски соответствуйт коротким воянам на квазистационарных атмосфернын фронтах.

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Dedicated to Professor Bedřich Ŝalamon on his 85th Birthday     

Pseudo relative velocity spectra of earthquake ground motion at high frequencies

The currently available empirical scaling laws for estimation of spectral amplitudes are limited to periods longer than 0–04 s. However, for design of equipment and stiff structures on multiple and distant supports, exposed to strong shaking near faults where peak accelerations can exceed 1g, specification of design ground motions at higher frequencies is required. This paper presents a method for extrapolation of pseudo-relative velocity spectral amplitudes of strong earthquake shaking to short periods (0–01 < T < 0–04 sec). The extrapolated spectra can be used as a physical basis for defining design spectral amplitudes in this higher-frequency range. The analysis in this paper implies that for typical strong motion accelerations, particularly on sedimentary sites in California, the peak ground accelerations are projected to be unaffected by frequencies higher than those recorded. Consequently, in California, the high-frequency pseudo-acceleration spectra can be approximated from the recorded absolute peak accelerations.     

Spatial ground motion effect on relative displacement of adjacent building structures

This paper analyses earthquake ground motion spatial variation effects on relative linear elastic response of adjacent building structures. It studies the relative importance of ground motion spatial variations and dynamic characteristics of adjacent structures in causing relative responses. Random vibration method is used in the study. It is found that, besides ground-acceleration-induced dynamic responses, quasi-static responses induced by spatially varying ground displacements also contribute significantly to the relative structural responses. The effects of spatial ground motions are very pronounced to the relative displacements of adjacent low-rise structures, and to those of high-rise adjacent structures with similar vibration characteristics. The effect of vibration properties of adjacent structures are, however, more significant to those of high-rise adjacent structures if they poses noticeably different vibration periods. Copyright © 1999 John Wiley & Sons, Ltd.     

Effects of relative motion between gas and liquid on 1-dimensional steady flow in silicic volcanic conduits: 1. An analytical method

We investigate the effects of vertical relative motion between gas and liquid on eruption styles by formulating a model for 1-dimensional steady flow in volcanic conduits. As magma ascends and decompresses, volatiles exsolve and volume fraction of gas increases. As a result, magma fragmentation occurs and the flow changes from bubbly flow to gas-pyroclast flow. In our model, a transitional region (‘permeable flow region’) is introduced between the bubbly flow region and the gas-pyroclast flow region. In this region, both the gas and the liquid are continuous phases, allowing the efficient vertical escape of gas through the permeable structure. We describe the features of conduit flow with relative motion of gas and liquid using non-dimensional numbers α, γ and ε. The parameter α represents the ratio of effects of wall friction to gravitational load, and is proportional to magma flow rate. The parameter γ represents the degree of decompression for the gas-pyroclast flow to reach the sound velocity at α = 1, and is proportional to r_c²/μ for given magma temperature and initial volatile content, where r_c is conduit radius and μ is liquid viscosity. The parameter ε is defined as the ratio of liquid–wall friction force to liquid–gas interaction force in the permeable flow region, and represents the efficiency of gas escape from magma. The values of γ and ε are determined only by magma properties and geological conditions such as liquid viscosity, magma permeability and conduit radius. We formulate a 1-dimensional steady-state conduit flow model to find non-dimensional magma flow rate α as a function of magma properties and geological conditions (e.g., γ and ε) under given boundary conditions. When the relative motion is taken into account with the assumption that magma fragmentation occurs when the gas volume fraction reaches some critical values, the pressure at the fragmentation level (P_f) decreases as the magma flow rate (α) decreases or the efficiency of gas escape (ε) increases, because gas escape suppresses the increase in the gas volume fraction accompanying magma ascent. When ε is so large that P_f is below the atmospheric pressure (P_a), the flow reaches the vent before fragmentation at low α. On the other hand, when ε is so small that P_f is greater than P_a, the flow reaches the vent after fragmentation at high α. These steady-state solutions of the flow at low and high α correspond to effusive and explosive eruptions, respectively. We present a graphical method to systematically find α. On the basis of the graphical method, a simple regime map showing the relationship between the assemblage of the solutions of conduit flow and the magma properties or the geological conditions is obtained.     

Relations between basal condition,subglacial hydrological networks and geothermal flux in Antarctica

When modelling the Antarctic ice sheet, the velocity of the ice flow is linked to its temperature. Depending on the thermal rate, the flow rate may vary between deformation and sliding. In this study, we focus on the geothermal flux because it is the least well-known component of the heat equation, and because it constrains the temperature at the bottom of the ice sheet. We used available geological data to build a map of the geothermal flux, which was found to increase from 51 mW/m² in East Antarctica to 68 mW/m² in West Antarctica. These values were integrated in the computation of a basal temperature map. The available map of hydrological networks clearly shows more melted areas in West Antarctica than in the earlier results. So we suggest that the model should be forced with higher geothermal flux values, over 85 mW/m² in this sector. This increase is in good agreement with published results which found a geothermal flux three times higher in West Antarctica. Finally, we computed the bottom melt rate over the ice sheet area which has a mean value of 3.5 mm/yr resulting in a lost of melted ice equal to 1% of the total mass balance.     

Coupling patterns between para‐glacial and permafrost degradation responses in Antarctica

The recently deglaciated environments in maritime permafrost regions are usually affected by very active paraglacial processes. Elephant Point is an ice‐free area of 1.16 km2 located in the SW of Livingston island (South Shetland Islands, Antarctica). Between 1956–2010 the retreat of the ice cap covering most part of this island has exposed 17.3% of the land surface in this peninsula. Two geomorphological units were identified in this new ice‐free area: a moraine extending from the western to the eastern coastlines and a relatively flat proglacial surface. The glacier in 1956 sat in contact with the northern slope of the moraine, but its accelerated retreat ‐ in parallel to the warming trend recorded in the Antarctic Peninsula ‐ left these areas free of glacier ice. Subsequently, the postglacial evolution was controlled by the relaxation phase typical of paraglacial systems. The typology and intensity of geomorphological processes show a significantly different dynamics between the southern and northern slopes of the moraine. This pattern is related to the different stage of paraglacial adjustment in both slopes. In the southern side, on coarser sediments, pronival ramparts, debris flows and alluvial fans are distributed, with a low to moderate activity of slope processes. In the northern side, mass wasting processes are extremely active on fine‐grained unconsolidated sediments. Ice‐rich permafrost is being degraded by thermokarst processes. Landslides and mudflows transfer large amounts of sediments down‐slope. The surface affected by retrogressive‐thaw slumps in the moraine has been quantified in 24,172 m2, which accounts for 9.6% of its surface. The abundance of kettle‐lakes is also indicative of the degradation of the ground ice. Paraglacial processes are expected to continue in the moraine and proglacial area in the near future, although their intensity and duration will depend on the magnitude and rate of future climate trends in the northern Antarctic Peninsula. Copyright © 2015 John Wiley & Sons, Ltd.     

A revised identification of the oldest sea-floor spreading anomalies between Australia and Antarctica

We propose that magnetic anomalies south of Australia and along the conjugate margin of Antarctica that were originally identified as anomalies 19 to 22 may be anomalies 20 to 34. The original anomaly identification has two troublesome aspects: (1) it does not account for an “extra” anomaly between anomalies 20 and 21, and (2) it provides no explanation for the rough topography comprising the Diamantina Zone. With our revised identification there is no “extra” anomaly and the Diamantina Zone is attributed to a period of very slow spreading (～4.5mm/yr half rate) between 90 and 43 m.y. The ages bounding the interval of slow spreading (90 and 43 m.y.) correspond to times of global plate reorganizations. Our revised identification opens up the possibility that part of the magnetic quiet zone south of Australia formed during the Cretaceous long normal polarity interval. Breakup of Australia and Antarctica probably occurred sometime between 110 and 90 m.y. B.P. The “breakup unconformity” identified by Falvey in the Otway Basin may correspond to a eustastic sea level change.     

中美两国最新地震动区划图的对比

本文介绍了中美两国地震动区划的技术方法、使用的资料、区划结果,并对两国的区划图特点进行对比分析,它们分别反映了两国地震科学研究的程度和抗震设防的水平,结果表明：中关两国具有相同的编图思路,具体技术方法和区划结果有一定的差别．     

Geochemical modelling and speciation studies of metal pollutants present in selected water systems in South Africa

Metal pollutants in water poses great threats to living beings and hence requires to be monitored regularly to avoid loss of lives. Various analytical methods are available to monitor these pollutants in water and can be improved with time. Modelling of metal pollutants in any water system helps chemists, engineers and environmentalists to greatly understand the various chemical processes in such systems. Water samples were collected from waste water treatment plant and river from highlands close to its source all the way to the ocean as it passing through areas with high anthropogenic activities. Pre-concentration of pollutants in the samples was done through acid digestion and metal pollutants were analysed using inductively coupled plasma-optical emission spectra (ICP-OES) to determine the concentration levels. Metal concentrations ranged between 0.1356–0.4658 mg/L for Al; 0.0031–0.0050 mg/L for Co, 0.0019–0.0956 mg/L for Cr; 0.0028–0.3484 mg/L for Cu; 0.0489–0.3474 mg/L for Fe; 0.0033–0.0285 mg/L for Mn; 0.0056–0.0222 mg/L for Ni; 0.0265–0.4753 mg/L for Pb and 0.0052–0.5594 mg/L for Zn. Modelling work was performed using PHREEQC couple with Geochemist’s workbench (GWB) to determine speciation dynamics and bioavailability of these pollutants. Modelling thus adds value to analytical methods and hence a better complementary tool to laboratory-based experimental studies.     

Effects of relative motion between gas and liquid on 1-dimensional steady flow in silicic volcanic conduits: 2. Origin of diversity of eruption styles

We investigate the origin of diversity of eruption styles in silicic volcanoes on the basis of a 1-dimensional steady conduit flow model that considers vertical relative motion between gas and liquid (i.e., vertical gas escape). The relationship between the assemblage of steady-state solutions in the conduit flow model and magma properties or geological conditions is expressed by a regime map in the parameter space of the ratio of liquid-wall friction force to liquid–gas interaction force (non-dimensional number ε), and a normalized conduit length Λ. The regime map developed in the companion paper shows that when ε is smaller than a critical value ε_cr, a solution of explosive eruption exists for a wide range of Λ, whereas an effusive solution exists only when Λ ~ 1. On the other hand, when ε > ε_cr, an effusive solution exists for a wide range of Λ. Diversity of eruption styles observed in nature is explained by the change in ε accompanied by the change in magma viscosity during magma ascent. As magma ascends, the magma viscosity increases because of gas exsolution and crystallization, leading to the increase in ε. For the viscosity of hydrous silicic magma at magma chamber, ε is estimated to be smaller than ε_cr, indicating that an explosive solution exists for wide ranges of geological parameters. When magma flow rate is small, the viscosity of silicic magma drastically increases because of extensive crystallization at a shallow level in the conduit. In this case, ε can be greater than ε_cr; as a result, a stable effusive solution co-exists with an explosive solution.     

The pattern of surface wind flow in Antarctica

Summary The main characteristics of surface winds are tabulated for 34 Antarctic stations. Using these data, supplemented by traverse records, the average wind flow is interpolated for each region and presented as a map showing the pattern of surface wind flow for the whole continent. Attention is focused on the flow in relation to surface contours. Statistics are presented for surface slope, wind speed, temperature, seasonal variations of speed and temperature, diurnal variation (including power spectra) of the wind speed and times of maximum and minimum speed at coastal and inland stations, wind frequency versus direction, the occurrence of calms, the deviation of the plateau wind from the downslope direction, the wind direction near the front of ice shelves, the proportion of cloud cover, and wind chill factors. In all cases data are grouped according to the environs of the stations in an attempt to isolate systematic differences depending on location: coastal stations near the foot of the ice slope and fully exposed to katabatic flow, coastal stations on offshore islands, coastal stations on peninsulas, coastal stations on extensive rock areas, ice shelf stations and inland stations.     

Site effect evaluation at Mexico City: Dominant period and relative amplification from strong motion and microtremor records

Site effects in Mexico City are discussed in terms of simple 1D, one-layer, linear models. The analysis is focussed on two parameters: dominant period and maximum amplification relative to a firm site within the city. The data used is a compilation of strong motion data and microtremor measurements. Strong motion data consist of digital acceleration records for nine events recorded by the Accelerographic Network of Mexico City. The authors analyzed spectral ratios of horizontal components of soft soil sites relative to an average of firm site observations for this data set. Dominant period, maximum relative amplification and an estimate of material damping were computed from the empirical transfer functions thus obtained. Microtremor data were compiled from measurement of different groups during the period 1985–1992. In all, 409 measurement points were analyzed. Values of dominant period obtained from microtremor measurements are in excellent agreement with those obtained from empirical transfer functions for strong motion data. The synthesis of results allows us to draw a detailed and robust map of dominant period for Mexico City. Based on this map, the authors propose some modifications to the current microzonation of Mexico City and evaluate a proposed model to account for site effects in this city.     

地震动强度非平稳特性参数与结构响应之间的近似定量关系分析

本文在对实际地震加速度记录统计分析的基础上,给出了能够合理描述地震动强度非平稳特性的参数及其取值范围;然后引入实验设计方法,建立了适合于地震动强度非平稳特性参数分析的实验设计算法,用来分析地震动强度非平稳特性参数的变化对结构响应的影响;最后通过与近似技术相结合,建立了地震动强度非平稳特性参数与结构响应之间的近似定量关系模型.结果表明,本文提出的实验设计方法适合于对地震动强度非平稳特性参数进行分析,该方法在有效地减小计算量的同时,获得了结构响应与参数变化之间的对应关系.基于实验设计方法进行的特性参数方差分析结果表明:地震动的稳态持时对结构地震响应的影响比较显著;对于周期较小的结构,特性参数之间的交互作用对结构地震响应的影响显著,但当周期大于1 s时,则不显著.本文建立的近似定量关系模型能够较好地反映不同特性参数、不同周期结构动力响应之间的联系,为工程实践中基于结构特性合理设置地震动特性参数、合成或挑选地震加速度时程提供理论依据.      

Relationship between magnetic activity in the polar cap and atmospheric processes in the winter Antarctica

The paper demonstrates the close relationships between the polar cap magnetic activity, which is characterized by PC index (Troshichev et al., 1988, Troshichev et al., 2006) and some atmospheric phenomena typical of the winter Antarctica, such as enhancement of cloudiness, sudden warmings of the ground atmosphere in near-pole area, and formation of anomalous wind regimes above Antarctica. It was shown previously (Troshichev et al., 2004, Troshichev et al., 2008, Troshichev and Janzhura, 2004) that these atmospheric phenomena are controlled by variations of the geoeffective interplanetary electric field impacting the Earth’s magnetosphere. On the other hand, the polar cap magnetic activity is also determined by the interplanetary electric field influence through the field-aligned magnetospheric currents and electric field in the polar cap ionosphere. The results imply that the PC index, available online at http://www.aari.nw.ru from the near-pole station Vostok, can be used to monitor the anomalous atmospheric processes in winter Antarctica.     

Separation and sliding between soil and structure during strong ground motion

This paper presents an approach to the problem of separation and sliding between soil and structure in the finite element analysis of dynamic soil-structure interaction problems. Joint elements are arranged along the contact surface between soil and structure and they have a property such that tensile forces are not transmitted between the planes representing structure and soil in the finite element analysis. The dynamic properties governing the sliding are determined by the Mohr-Coulomb failure law determined from the cohesion and the friction angle between soil and structure. The proposed method is applied to (i) a model of a reactor building resting on the free surface of layered ground and (ii) a buried foundation structure. The numerical computations reveal the following results: that the translation is dominant in the motion of the structure when sliding is taking place between soil and structure, and that the rocking is dominant in the rest of the response. The amplitude of the response during sliding is increased on any one point of the structure and decreased on any one point of the ground compared with that of the fixed condition at the interface. In the case of the buried structure, it is observed in the computed results that the structure and soil move in the opposite direction along the vertical contact surface and are separated from each other in the near surface region during the strong phase of the excitation.     

Characterizing incipient motion of low fines content soils with varying compositions,water contents,and relative densities

Laboratory flume experiments were conducted to quantify the effects of the soil characteristics on the critical shear stress of low fines content soil samples collected from the Montauk shores in New York. The collected soils were reconstituted at five different fines contents, ranging between 0 and 20%. These soil mixtures were composed of two initial water contents, dry of optimum and optimum moistures, and two relative densities, one moderate dense and the other dense. The strength indices of...