A Condition for Super-shear Rupture Propagation in a Heterogeneous Stress Field   总被引：1，自引：0，他引：1  

E. Fukuyama  K. B. Olsen 《Pure and Applied Geophysics》2002,159(9):2047-2056

— We have used numerical simulations with the boundary integral equation method to investigate a mechanism to excite super-shear rupture velocities in a homogeneous stress field including an asperity of increased initial stress. When the rupture, with the slip-weakening distance selected to generate sub-Rayleigh speed, encounters the asperity it either accelerates to super-shear velocities or maintains the sub-Rayleigh speed, dependent on the size and amplitude of the asperity. Three classes of rupture propagation are identified: the velocity (a) for the most narrow asperities increases slowly towards the Rayleigh wave speed, (b) for intermediate width of the asperities jumps to super-shear values for a short distance but then decreases to sub-Rayleigh wave speeds, and (c) for the widest asperities jumps to super-shear values and pertains to values between the S- and P-wave velocities. The transitions between the three classes of rupture propagation are characterized by very narrow (critical) ranges of rupture resistance. If the size of the initial asperity is smaller than critical, it becomes difficult for rupture to propagate with super-shear velocities even if the initial stress level is high. Our results suggest that stress variation along the rupture path helps homogenize the rupture velocity and propagate with sub-Rayleigh wave speeds.  相似文献   

The Antarctic achondrite ALHA 76005: a polymict eucrite     

Lawrence Grossman  Edward Olsen  Andrew M. Davis  Tsuyoshi Tanaka  Glenn J. MacPherson 《Geochimica et cosmochimica acta》1981,45(8):1267-1279

ALHA 76005 is a basaltic achondrite containing few. if any, orthopyroxenes. Its bulk major and trace element composition is like that of a non-cumulate eucrite, and unlike that of a howardite. It contains a variety of igneous clasts which differ in their textures, pyroxene/plagioclase ratios and pyroxene and plagioclase compositions. One clast, No. 4, was found to have the REE pattern of a cumulate eucrite and an oxygen isotopic composition different from that of the bulk meteorite. Both the chemical and oxygen isotopic composition of clast No. 4 suggest that it was derived from a source different from its host. These observations lead to the conclusion that ALHA 76005 is a polymict eucrite.  相似文献   

Composition of metal in type III carbonaceous chondrites and its relevance to the source-assignment of lunar metal     

Louis H. Fuchs  Edward Olsen 《Earth and Planetary Science Letters》1973,18(3):379-384

The metal in seven Type III carbonaceous chondrites has been measured for concentrations of Ni, Co and Cr. Cobalt in kamacite is 3.2 to 5.5 times greater than in taenite on composite grains containing both phases. No correlation was found between the metal compositions and sub-type classification. Ni and Co contents of kamacite from several of the Type III's studied fall outside of the range for these elements in bulk meteoritic metal and are relevant to the assignment of a meteoritic vs a non-meteoritic origin for lunar metal particles in the fines and breccias.  相似文献   

Biophysical impacts of climate change on some terrestrial ecosystems in Estonia     

Are Kont  Jaak Jaagus  Tõnu Oja  Arvo Järvet  Reimo Rivis 《GeoJournal》2002,57(3):169-181

Climate warming due to the enhanced greenhouse effect is expected to have a significant impact on the natural environment and human activity in high latitudes. Because of its geography, wide coastal areas, water resources, forests, and wetlands, the environment of Estonia is sensitive to climate change and sea level rise. Climate change scenarios for Estonia were generated using a Model for the Assessment of Greenhouse-gas Induced Climate Change (MAGICC) and a regional climate change database, Scenario Generator (SCENGEN). Three alternative emission scenarios were combined with data from 14 general circulation model experiments. The assessment results of forest resources using RipFor, a forest-soil-atmosphere model, show that climate warming would enhance forest growth in Estonia resulting in increased productivity (2–9%) of harvestable timber on highly productive sites. Nutrient mobility increases greatly and in highly permeable soils with stable vegetation, increased mobility may result in nutrient losses through leaching. The assessment results of water resources using the simple water balance model, WatBal, show that the runoff regime of Estonian rivers would equilibrate and the groundwater table would rise. Climate warming would not cause any particular problems with water supply but the groundwater quality may suffer from increased leaching. Due to milder winters and increased storminess, the destruction of coastal areas, inundation of wetlands and disappearance of rare plant communities in coastal areas would be the most damaging results of climate change. Most sandy beaches high in recreational value would disappear. However, isostatic uplift and settlements inland from the present coastline reduce the risk of socio-economic decline. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Flow and transport through clay membrane barriers     

Michael A. Malusis  Charles D. Shackelford  Harold W. Olsen 《Engineering Geology》2003,70(3-4):235-248

Flux equations for liquid and solute migration through clay barriers that behave as semi-permeable membranes used in waste containment and remediation applications, known as clay membrane barriers (CMBs), are discussed. The results of a simplified analysis of flow through a geosynthetic clay liner (GCL) using measured values for the chemico-osmotic efficiency coefficient (ω) of the GCL indicate a total liquid flux that counters the outward Darcy (hydraulic) flux due to chemico-osmosis associated with clay membrane behavior of the GCL. Also, the solute (contaminant) flux through the GCL is reduced relative to the solute flux that would occur in the absence of membrane behavior due to chemico-osmotic counter advection and solute restriction. Since diffusion commonly controls solute transport through GCLs and other low-permeability clay barriers, the implicit (empirical) correlation between ω and the effective salt-diffusion coefficient of the migrating contaminant is an important consideration with respect to contaminant restriction in CMBs.  相似文献   

Non-iterative multiple-attenuation methods: linear inverse solutions to non-linear inverse problems – II. BMG approximation     

Luc T. Ikelle  Are Osen  Lasse Amundsen  Yunqing Shen 《Geophysical Journal International》2004,159(3):923-930

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Paleoshoreline geomorphology of Böön Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia     

Goro Komatsu  P. Jeffrey Brantingham  John W. Olsen  Victor R. Baker 《Geomorphology》2001,39(3-4)

We conducted a preliminary study of paleoshoreline features associated with Böön Tsagaan Nuur, Tsagaan Nuur, and Orog Nuur, lakes located in the Gobi–Altai transition zone of the Valley of Lakes (Dolina Ozor) which stretches from central to western Mongolia. The paleoshoreline features were first identified on RADARSAT satellite SAR imagery. We investigated the features during the 1998 field season of the Joint Mongolian–Russian–American Archaeological Expedition to the Gobi–Altai region. We identified paleoshorelines of multiple elevations in the field, which are considered to be relict beach ridges and wave-cut terraces. Other paleolake landforms include spits and Gilbert-type deltas. These landforms are complex, large and well established, implying that the paleolakes were stable for extended periods. The reconstructed paleolakes cover extensive areas of the valley floor, implying that hydrological and climatic conditions were very different in the past. Paleolake expansions may have occurred under a variety of circumstances. One hypothesis is that the high lake stands occurred during the wetter period corresponding to the Oxygen Isotope Stage 3 prior to the Last Glacial Maximum (LGM), during the warmest early Holocene and the late Holocene, or during all these periods. If low evaporation rates due to lower temperatures, glacier meltwater and possibly increased precipitation are important factors, then the expansions may have occurred during the terminal Late Glacial period after the Last Glacial Maximum. The greatly expanded lakes in the Gobi–Altai could have significantly affected the Quaternary human demography and migration in the region.  相似文献   

High-density CO2 inclusions in the Colorado Front Range   总被引：1，自引：0，他引：1  

Sakiko N. Olsen 《Contributions to Mineralogy and Petrology》1988,100(2):226-235

A fluid density in an inclusion is commonly observed to be too low for the P-T estimates for the postulated time of trapping, and is generally attributed to a fluid loss during the uplift process. It is more difficult to explain a fluid density which is too high. In the 1700 m.y. Front Range migmatites, such high densities occur in some of CO₂ inclusions which were deduced to have formed during the migmatization episode. The peak P-T estimates for migmatization in the Front Range are 4–6 kb and 650°–700° C (in sillimanite field) but pressures required to form the most dense inclusions are >7.6 kb (in kyanite field). The high density is not likely to be a relic of a higher pressure condition earlier than the main migmatization episode for the following reasons: (a) no kyanite (or any other relic high pressure phase) has been found in the Precambrian Front Range; (b) the high density inclusions are rare in zones with least signs of deformation and melting (paleosomes and quartz inclusions within feldspar grains) which instead contain relatively undisturbed early inclusions; (c) high density inclusions with Th <–30° C are associated with heavily altered plagioclase caused by hydrothermal activity which was a late event in leucosome formation. Further, there is evidence for post-entrapment change(s) in density: an intragranular trail in quartz contains CO₂ inclusions that exhibit almost the whole range in Th (–40 to +24° C) as displayed by the entire population of the early CO₂ inclusions (–66 to +30° C). The density of an inclusion in the trail is not related to inclusion size but to the position of the inclusion relative to apparent micro-shear zones crossing the CO₂ trail. A change to a higher density (=a smaller volume) could have resulted from an initially isobaric cooling path which intersects CO₂ isochores with increasingly higher densities. Additional excess pressure may have resulted from overthrusting. However, because high density inclusions occur selectively in the zones in which plagioclase shows alteration indicating a high and because there is a correlation between shear zones and high density inclusions, it is postulated that local hydrolytic weakening of quartz was necessary for the decrease of inclusion volume which occurred during deformation. The localized deformation may also result in an excess pressure. However, the introduction of a small amount of H₂O into these inclusions as a possible cause of high density inclusions cannot be ruled out.  相似文献   

Plutonium and radiocesium in the water column of the Hudson River estuary     

P. Linsalata  H. J. Simpson  C. R. Olsen  N. Cohen  R. M. Trier 《Environmental Geology》1985,7(4):193-204

Isotopes of plutonium (Pu), cesium (Cs), and cobalt (Co) introduced into the Hudson River Estuary from fallout deposition, the erosion of fallout-contaminated surface soils, and nuclear reactor effluent (isotopes of Cs and Co only) have been measured in water column samples collected from 1975 to 1980 Isotopic measurements conducted independently by two research groups utilizing different sampling and analytical techniques have been summarized. The major conclusions drawn from the work are that for water samples collected by the two laboratories over similar time periods, the mean concentrations of nonfilterable^239,240Pu (<0.45 μm) were identical at 0.13 fCi/l, mean concentrations of both¹³⁷Cs and^239,240Pu in suspended particulates were more divergent at 2,270±920 pCi/kg (±1 SD) and 1,430±430 pCi/kg for¹³⁷Cs, and 19±8 pCi/kg and 12±4 pCi/kg for^239,240Pu The behavior of^239,240Pu and¹³⁷Cs within the water column is shown to diverge within brackish waters Specifically, the magnitude of the¹³⁷Cs distribution coefficient (K _d ) can be expressed as an inverse power function of the chloride ion concentrations for chlorinities between 0.1 and 4 g Cl⁻/l No difference in the^239,240PuK _d has been observed between fresh and brackish waters Based on the expected inventories of^239,240Pu and¹³⁷Cs within watershed soils, the current downstream transport of these radionuclides represents fractional mobilization rates on the order of 1–4 (×10⁻⁴) per year  相似文献   

Modeling short-period crustal phases ($\text{P}$, Lg) for long-range refraction profiles     

K.H. Olsen  L.W. Braile  J.N. Stewart 《Physics of the Earth and Planetary Interiors》1983,31(4):334-347

The short-period seismic phases known as $\text{P}$ and Lg are often recorded at distances of 200–1000 km on long-range refraction profiles and are usually the largest-amplitude features on record sections for this distance range. $\text{P}$ and Lg propagate as multiply reflected compressional and shear waves in a crustal waveguide whose principal boundaries are the Moho and the free surface. Equivalently, they can be interpreted as the interference pattern produced by a superposition of higher-mode P, SV and SH waves propagating in a leaky waveguide. For compressional waves, the waveguide efficiency is a strong function of frequency and depends on the presence or absence of low-velocity layers within a few kilometers of the surface, such as deep sedimentary sections commonly found in active tectonic areas. Such low-velocity surface layers create constructive interference effects for upcoming P waves incident at near grazing angles at the free surface and lead to efficient $\text{P}$ propagation. Several good examples of strong $\text{P}$ phases can be found on long-range refraction profiles for the tectonically active western United States; the 550 km profile eastward from SHOAL to Delta, UT is analyzed here. We have used a modified reflectivity-method computer program to model crustal phases for the SHOAL-Delta profile. The reflectivity technique accounts for all body and surface waves contributing to the short-period seismograms. It is found that the synthetic waveforms realistically model the observed $\text{P}$ characteristics. In this case, the decay of $\text{P}$ amplitudes with distance appears to be dominated by surface-reflection leakage from the waveguide rather than by anelastic attenuation due to Q of crustal rocks.  相似文献