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  • Articles  (90,158)
  • 1975-1979  (90,158)
  • Geosciences  (90,158)
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  • 1
    Electronic Resource
    Electronic Resource
    Clay gouges in the San Andreas Fault System and their possible implications (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 87-95 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary In the northern and central sections of the San Andreas Fault Zone, and along Calaveras and Hayward faults, clay gouges have been found to occur on the surface and at shallow depths. It is consistent with the available geochemical data that such gouges can exist at depths down to 10 km. If extensive gouge materials exist in a fault zone then their properties will determine, to a large extent, the behavior of the fault. From known properties of clays in the presence of water we can infer that, in such cases, the tectonic stress and the stress drops for earthquakes will be low and substantial creep will take place before earthquakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592901
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetism of rocks and volumetric strain in uniaxial failure tests (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 107-118 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary The relation between remanent magnetization and volumetric strain for gabbro samples stressed in uniaxial compression inside a near zero-field μ-metal shield has been examined. For samples with an induced IRM parallel to the axis of compression, remanent magnetization decreased linearly up to the onset of dilatancy. As increased stress produced additional dilatancy, the variation of remanent magnetization became nonlinear, and the stress dependence continually decreased until the rock failed. Stress cycling with the peak stress augmented for each cycle produced a continuous decrease in the zero stress value of the IRM although an appreciable amount of recovery was observed during unloading. When the sample was loaded in constant stress increments after the onset of dilatancy and held for several minutes at each level, time-dependent variations in remanent magnetization coincided with time-dependent increases in inelastic volumetric strain. In general as the inelastic creep rate increases, the rate of change in remanent magnetization increases. These results suggest that dilatancy related effects of the intensity of rock magnetization should be observed in magnetic rocks in epicentral regions prior to earthquakes and may serve as both long- and short-term precursors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592903
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  • 3
    Electronic Resource
    Electronic Resource
    An analysis of local changes in gravity due to deformation (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 97-106 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Deformation causes changes in gravity even though the measuring station is fixed relative to the center of the earth and the total mass in the vicinity of the station does not change. Deformation has two effects: the density at a point changes in response to changes in local stresses and the point itself moves relative to the station. The general expression derived here shows that the gravity change depends on the uplift immediately beneath the station and the deformation of cavities at depth — cracks, pores, magma reservoirs, etc. The approximation is made that density is uniform except for cavities, but no assumptions about the constitutive behavior of the medium are necessary. The gravity change studied here shows interesting analogies with the gravity effect due to buried bodies with anomalous density. For example, I find that the net volume change due to deformation can be found by integrating the gravity anomaly over the earth's surface, in analogy with the calculations for excess mass. The theory is especially useful when both deformation and net fluid flow into or out of the system occurs. The results are applied to uplift and gravity changes observed during the great Alaskan earthquake, the Matsushiro earthquake swarm, and a draw-down operation at the Wairakei geothermal field. The data at Wairakei are used to estimate the net amount of water taken from the aquifer. The data at Matsushiro is not sufficiently precise to discriminate between the various mechanisms that have been proposed, but the Alaskan earthquake data suggest that no dilatancy or fluid flow occurred between the survey in 1962 and the resurvey in 1964 just after the event.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592902
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  • 4
    Electronic Resource
    Electronic Resource
    Dilatancy model and empirical formulas for an earthquake area (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 141-147 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary A physical interpretation of empirical formulas for earthquake magnitude (M) and spatial extents of land deformation and aftershock area is attempted on the basis of a dilatancy model. It is demonstrated that the precursor time interval (τ) vs.M relation approximately fits in that for the τ vs. typical length of earthquake zone provided the above formulas hold good. A diffusion process in a dilatant region seems also to account for these approximate formulas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592906
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  • 5
    Electronic Resource
    Electronic Resource
    Two models for earthquake forerunners (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 169-181 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Similar precursory phenomena have been observed before earthquakes in the United States, the Soviet Union, Japan, and China. Two quite different physical models are used to explain these phenomena. According to a model developed by US seismologists, the so-called dilatancy diffusion model, the earthquake occurs near maximum stress, following a period of dilatant crack expansion. Diffusion of water in and out of the dilatant volume is required to explain the recovery of seismic velocity before the earthquake. According to a model developed by Soviet scientists growth of cracks is also involved but diffusion of water in and out of the focal region is not required. With this model, the earthquake is assumed to occur during a period of falling stress and recovery of velocity here is due to crack closure as stress relaxes. In general, the dilatancy diffusion model gives a peaked precursor form, whereas the dry model gives a bay form, in which recovery is well under way before the earthquake. A number of field observations should help to distinguish between the two models: study of post-earthquake recovery, time variation of stress and pore pressure in the focal region, the occurrence of pre-existing faults, and any changes in direction of precursory phenomena during the anomalous period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592908
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  • 6
    Electronic Resource
    Electronic Resource
    The sliding characteristics of sandstone on quartz fault-gouge (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 69-86 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Three types of triaxial compression experiments are used to characterize the frictional processes during sliding on quartz gouge. They are: 1) pre-cut Tennessee Sandstone sliding on an artificial layer of quartz gouge; 2) fractured Coconino Sandstone sliding along experimentally produced shear fractures; and 3) a fine-grained quartz aggregate deformed in compression. The specimens were deformed to 2.0 kb confining pressure at room temperature and displacement rates from 10−2 to 10−5 cm/sec dry and with water. There is a transition in sliding mode from stick-slip at confining pressures〈0.7 kb to stable sliding at〉0.7 kb. This transition is accompanied by a change from sliding at the sandstone-gouge contact (stick-slip) to riding on a layer of cataclastically flowing gouge (stable sliding). Quartz gouge between the pre-cut surfaces of Tennessee Sandstone lowers both the kinetic coefficient of friction and the magnitude of the stick-slip stress drops compared to those for a pre-cut surface alone. Stick-slip stress drops are preceded by stable sliding at displacements of 10−5 cm/sec. For a decrease in displacement rate between 10−3 and 10−5 cm/sec, stress-drops magnitudes increase from 25 to 50 bars. Tests on saturated quartz gouge show sufficient permeability to permit fluidpressure equilibrium within compacted gouge in 10 to 30 seconds; thus the principle of effective stress should hold for the fault zone with quartz gouge. Our results suggest that at effective confining pressures of less than 2.0 kb, if a fault zone contains quartz gouge, laboratory-type stick-slip can be an earthquake-source mechanism only if a planar sliding-surface develops, and then only when the effective confining pressure is less than 0.7 kb.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592900
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  • 7
    Electronic Resource
    Electronic Resource
    Dilatancy and crustal uplift (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 119-125 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Opening of cracks before an earthquake (dilatancy) causes inelastic crustal uplift. Raising the pore pressure in these cracks as pore fluid diffuses into the dilatant zone produces further elastic uplift. Since the time between resaturation of the dilatant zone and the earthquake is shorter than the life of thev p /v s anomaly, the elastic uplift is less than the inelastic. The magnitude of thev p /v s anomaly gives a lower bound on the compressibility of the dilatant zone. Velocity and uplift measurements lead to the conclusion that if dilatancy occurred before the 1971 San Fernando earthquake, the pore pressure in the hypocentral region at the time of the event must have been at least an order of magnitude below hydrostatic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592904
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  • 8
    Electronic Resource
    Electronic Resource
    The short-term influence of various concentrations of atmospheric carbon dioxide on the temperature profile in the boundary layer (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 331-353 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary A radiative-conductive model is constructed to study short-term effects of various carbon dioxide concentrations on the atmospheric boundary layer for different seasons. The distribution of the exchange coefficient is modeled with the aid of the KEYPS formula. Infrared radiation calculations are carried out by means of the emissivity method and by assuming that water vapor and carbon dioxide are the only radiatively active gases. Global radiation is computed by specification of Linke's turbidity factor. It is found that doubling the carbon dioxide concentration increases the temperature near the ground by approximately one-half of one degree if clouds are absent. A sevenfold increase of the present normal carbon dioxide concentration increases the temperature near the ground by approximately one degree. Temperature profiles resulting from presently observed carbon dioxide concentration and convective cloudiness of 50% or less are compared with those resulting from doubled carbon dioxide concentrations and the same amounts of cloud cover. Again, it is found that a doubling of carbon dioxide increases the temperature in the lower boundary layer by about one-half of one degree. The present results are obtained on the basis of fixed temperature boundary conditions as contrasted to the study ofManabe andWetherald (1967). Howeve, the conclusions are not addressed to global climate change, but to the distribution of the temperature of the air layer near the ground.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592922
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  • 9
    Electronic Resource
    Electronic Resource
    Computer aided contour plotting of geophysical survey data (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 419-433 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Geophysical survey data represent a class of information currently subjected to computer contouring techniques. The gridded network is a feature inherent to a large portion of these surveys. Taking advantage of this feature, a simple and highly efficient computer program has been developed, minimizing the contouring effort in terms of the money, time and programming involved in the interpretation process. The program includes interpolation between data points in two directions, determination of contour line coordinates, and subsequent plotting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592928
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  • 10
    Electronic Resource
    Electronic Resource
    A theoretical model of the dilatant behavior of a brittle rock (1975)
    Springer
    Pure and applied geophysics 113 (1975), S. 183-196 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary A dilatancy model is presented which seems capable of simulating the results of laboratory tests on rock samples. The fundamental assumption incorporated in the model is that dilatancy is caused by the opening of cracks, where the cracks open in the least compressive stress direction (Brace et al., 1966). Its simplicity and compatibility with numerical techniques, involving the simulation of both static and dynamic stress fields, permits prediction of dilatancy induced effects for stress states and loading conditions which are not experimentally attainable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01592909
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