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1.
Seismic hazard maps of the Los Angeles metropolitan area are illustrated for normalized peak strain and for 50 years of exposure. The strain estimates are based on scaling in terms of peak ground velocity. The proportionality factor is the phase velocity with which the wave energy is propagating. A simplified seismicity model is used in which all earthquakes occur on faults represented by buried lines and in one zone of diffused seismicity. Poissonian model of earthquake occurrence is assumed. The same model was used in the 1980's to illustrate a method for microzoning of the same area for response spectral amplitudes. Maps of logarithms of normalized peak strain, cεmax, are presented for probabilities of at least one exceedance p = 0·99, 0·9, 0·5, 0·1 and 0·01. These can be used to construct site specific probability distribution functions of the normalized peak strain, cεmax. Such maps are useful for design of new and for retrofit of existing structures, sensitive to strain and differential ground motions (bridges, tunnels, pipelines, etc.).  相似文献   

2.
Paleomagnetic data from 46 sites (674 specimens) of the Westcoast Crystalline Gneiss Complex on the west coast of Vancouver Island using AF and thermal demagnetization methods yields a high blocking temperature WCB component (> 560°C) with a pole at 335°W, 66°N (δp = 4°, δm = 6°) and a lower coercivity WCA component ( 25 mT, < 500°C) with a pole at 52°W, 79°N (δp = 7°, δm = 8°). Further thermal demagnetization data from 24 sites in the Jurassic Island Intrusions also defines two high blocking temperature components. The IIA component pole is at 59°W, 79°N (δp = 7°, δm = 8°) and IIB pole at 130°W, 73°N (δp = 12°, δm = 13°). Combined with previous data from the Karmutsen Basalts and mid-Tertiary units on Vancouver Island and from the adjacent Coast Plutonic Complex, the geotectonic motions are examined for the Vancouver Island segment of the Wrangellian Subterrane of composite Terrane II of the Cordillera. The simplest hypothesis invokes relatively uniform translation for Terrane II from Upper Triassic to Eocene time producing 39° ± 6° of northward motion relative to the North American craton, combined with 40° of clockwise rotation during the Lower Tertiary.  相似文献   

3.
Many free and forced vertical vibrations tests were conducted on surface and embedded models for footings on dry and moist poorly graded sand that has the following properties: D10 = 0·21 mm, D30 = 0·305 mm, D60 = 0·423 mm, Cu = 2, Cc = 1·05, Gs = 2·66, γmax = 1·74 cm−3 and γmin = 1·4 g cm−3. The tests were conducted at relative density Dr = 82%. The effect of mass, area, geometry, embedment, saturation, load amplitude and frequency were studied. For this purpose square, rectangular and circular models of concrete footings were chosen. Swieleh sand was chosen as the foundation soil. Results have been obtained for models having different mass, same base shape and area; models of different base area and equal base shape and mass; and models of different base shape geometry and about equal masses and base areas.Forced vertical vibration tests results showed an increase in natural frequency and a reduction in amplitude with the increase in embedment depth, degree of saturation and footing base area. Increasing the mass of model footing resulted in a decrease in the natural frequency while the dynamic response increased. Also, results showed that the circular model footing gives low values of dynamic response in comparison to other models.Free vertical vibration test results showed an increase in damping ratio with increase in the base area of the model footing, depth of embedment and saturation of sand. On the other hand, the results showed a decrease in damping ratio with increase in the footing mass. Circular footing gives the highest value of damping ratio among other footings.Results showed that the best method for evaluating the dynamic stiffness for vertical vibration is using Dobry and Gazetas1 (J. Geotech. Engng, ASCE, 1986, 112, 109–133) equations together with the formula proposed by Ronald and Bojan2 (J. Geotech. Engng, ASCE, 1995, 121, 274–286) for evaluating the equivalent shear modulus.  相似文献   

4.
The geological evolution of the Mesozoic Troodos Ophiolite Complex in Cyprus, and the tectonic nature and timing of the palaeomagnetically indicated anticlockwise rotation of Cyprus of some 80° and ca. 15° northward translation, have been open for debate for some time. New palaeomagnetic data from 18 sites ( 180samples) in the post-ophiolite sediments, ranging in age from Upper Cretaceous to Upper Miocene, are presented. Most of the sites are of normal geomagnetic polarity, but indications of reversed polarity have been found in an older group of sediments (the Lefkara Formation of Upper Palaeocene age).Six sites from the older group of sediments (Upper Cretaceous to Eocene in age) give a site mean direction of the AF cleaned sediments of (D, I) = (323°, 29°) with α95 = 18°, while 5 sites from a younger group of sediments (Oligocene to Miocene in age) give a cleaned site mean direction of (D, I) = (334°, 58°) with α95 = 9°. These and published data suggest that an anticlockwise rotation of Cyprus of 60 ± 10° occurred early during the post-igneous evolution of the Cyprus oceanic crust between 90 and 50Ma, leaving only a minor anticlockwise rotation of 20 ± 10° to occur during the last 50 Ma. It is furthermore concluded that the northward translation of Cyprus of 15° mostly took place during the last 30Ma.It thus appears that a fairly rapid rotation of the Cyprus microplate first took place in the Late Cretaceous and Early Tertiary time with an average angular velocity of 1–2°/Ma, during which the northward translation was minor or negligible. In the latter half of the Tertiary, the sense of movement appears to have radically changed, the northward translation now being dominant with an average velocity of 5–6cm/yr. This temporal evolution is found to be in good agreement with the Mesozoic and Tertiary movements of the African lithospheric plate relative to Europe, as evidenced from the Atlantic sea-floor magnetic anomaly spreading history.  相似文献   

5.
The equilibrium distribution of CO2H2O fluids in synthetic rock samples (principally dunite and quartzite) has been characterized by measurements of the dihedral wetting angle, θ, resulting from 5-day annealing periods at 950–1150°C and 1 GPa. For fluids in equilibrium with polycrystalline quartz, θ varies systematically from 57° for pure H2O to 90° at XCO2 0.9. Similarly, for San Carlos olivine, θ varies from 65° for pure H2O to 90° at XCO2 0.9. The addition of solutes (NaCl, KCl, CaF2, Na2CO3) to H2O causes a major decrease in θ in the quartz/fluid system (to values as low as 40°), but has no effect on fluid wetting in dunite. Reconnaissance experiments on other mono- and polymineralic aggregates indicate universally high wetting angles (θ 60°) in upper mantle assemblages and for CO2 in felsic compositions. For diopside + H2O, θ 80°, with large variation due to crystalline anisotropy. In no case does θ approach 0°, the condition necessary for fluid to be present along all grain boundaries.Because a value of θ greater than 60° precludes the existence of an interconnected fluid phase in a rock, our results have important implications not only for fluid transport but also for the physical properties of the bulk fluid/rock system. Any static fluid present in the upper mantle must exist as isolated pores located primarily at grain corners, and transport can occur only by hydrofracture. In the continental crust, aqueous fluids (especially saline ones) are likely to form an interconnected network along grain edges, thus contributing to high electrical conductivity and allowing the possibility of fluid transport by porous flow or surface energy-driven infiltration.  相似文献   

6.
It is widely recognized that lavas behave as Bingham liquids, which are characterized by a yield stress σ and a plastic viscosity η. We consider two models describing downslope flows of a Bingham liquid with different aspect ratios A (= flow height/flow width): model 1 with A 1 and model 2 with A ≈ 1. Sufficiently uphill with respect to the front, such flows can be considered as laminar and locally isothermal. For both models, we obtain analytically the steady-state solution of the Navier-Stokes equations and the constitutive equation for a Bingham liquid. We study the flow height and velocity as functions of flow rate, rheological parameters and ground slope. It is found that such flows remain in the Newtonian regime at low yield stresses (σ 103dyne/cm2), but the transition to the Bingham regime also depends on flow rate and occurs at higher values of σ for higher flow rates: for instance, a high aspect ratio flow (model 2) is still very close to the Newtonian regime at σ = 104 dyne/cm2, if the flow rate is greater than 105 g/s. In the Bingham regime, flow heights are generally greater and flow velocities are smaller than in the Newtonian regime; moreover, flow heights are independent of flow rate, so that a change in flow rate results exclusively in a velocity change. After assuming a specific temperature dependence of σ and η between the solidus and the liquidus temperatures of an ideal Bingham liquid (1000°C and 1200 °C respectively), flow heights and velocities are examined as functions of temperature along the flow. Several effects observed in lava flows are predicted by these models and allow a more quantitative insight into the behaviour of lava flows.  相似文献   

7.
We carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the Matsuura district, SW Japan, at subliquidus temperatures from 1230 °C to 1140 °C under 1 atm with NNO oxygen buffered conditions. Viscosity increased from 31 to 1235 Pa s with a decrease in temperature from 1230 to 1140 °C. On cooling, olivine first appeared at 1210 °C, followed by plagioclase at 1170 °C. The crystal content of the sample attained 31 vol.% at 1140 °C (plagioclase 22%, olivine 9%). Non-Newtonian behaviors, including thixotropy and shear thinning, were pronounced in the presence of tabular plagioclase crystals. The cause of such behavior is discussed in relation to shear-induced changes in melt–crystal textures. Relative viscosities, ηr (= ηs / ηm, where ηs and ηm are the viscosities of the suspension and the melt, respectively), were obtained by calculating melt viscosities from the melt composition and temperature at 1 atm using the equation proposed by Giordano and Dingwell [Giordano, D., Dingwell, D.B., 2003. Non-Arrhenian multicomponent melt viscosity: a model. Earth and Planetary Science Letters, 208, 337–349.]. The obtained relative viscosities are generally consistent with the Einstein–Roscoe relation, which represents ηr for suspensions that contain equant and equigranular crystals, even though the crystal suspension analyzed in the present experiments contained tabular plagioclase and granular olivine of various grain sizes. This consistency is attributed to the fact that the effect of crystal shape was counterbalanced by the effect of the dispersion of crystal size. The applicability of the Einstein–Roscoe equation with respect to crystal shape is discussed on the basis of the present experimental results. Our experiments and those of Sato [Sato, H., 2005. Viscosity measurement of subliquidus magmas: 1707 basalt of Fuji volcano. Journal of Mineralogical and Petrological Sciences, 100, 133–142.] show that the relationship between relative viscosity and crystal fraction is consistent with the Einstein–Roscoe relationship for axial ratios that are smaller than the critical value of 4–6.5, but discrepancies occur for higher ratios.  相似文献   

8.
For transient, high frequency, and pulse like excitation of structures in the near field of strong earthquakes, the classical design approach based on relative response spectrum and mode superposition may not be conservative. For such excitations, it is more natural to use wave propagation methods. In this paper (Part I), we review several two-dimensional wave propagation models of buildings and show results for theoretical dispersion curves computed for these models. We also estimate the parameters of these models that would correspond to a seven-story reinforced concrete building in Van Nuys, California. Ambient vibration tests data for this building imply vertical shear wave velocity βz=112 m/s and anisotropy factor βx/βz=0.55 for NS vibrations, and βz=88 m/s and βx/βz=1 for EW vibrations. The velocity of shear waves propagating through the slabs is estimated to be about 2000 m/s. In the companion paper (Part II), we estimate phase velocities of vertically and horizontally propagating waves between seven pairs of recording points in the building using recorded response to four earthquakes.  相似文献   

9.
A series of cyclic triaxial tests on clayey sands was carried out and attempts were made to evaluate the strain dependency of shear modulus and damping. Strain dependencies of shear modulus and damping were simply modeled. It was shown that the change in the effective confining stress with loading cycles in the undrained shear test needed to be considered particularly in the large strain range. The consideration could be made by normalizing G with G′0=AF(e)(σ′m/σmr)n, the initial shear modulus for the effective confining stress of that particular loading cycle, instead of using G0. G/G′0 was expressed by a function of γ as G/G′0=1/(1+bgγ) which was almost stress level independent for clayey sands used in this study. The damping ratio was not much affected by the confining stress. The strain dependency of the damping ratio was modeled by h=ahγ/(1+bhγ). Effects of load irregularity on the shear modulus were also investigated. The excess pore pressure and the residual strain were generated especially when the major peaks in the irregular loading were applied to the specimen. However, G/G′0 for the irregular loading could be represented reasonably well by the average curve for the uniform cyclic loading, if the excess pore water pressure and the residual strain were taken into account.  相似文献   

10.
Partial reflection differential absorption and differential phase observations have been used to systematically study collision frequencies (ν) in D-region of the lower ionosphere. The observations made with the large MF radar located at Buckland Park (35°S, 138°E) near Adelaide in the period September 1996–December 2000 show ν values larger than predicted by previously used models. The new estimates are compared with values calculated using new collision frequency momentum cross-sections for N2(σ) measured in the laboratory. The two types of measurements are found to be in good agreement, with a moderate seasonal variation of ν at a constant height. No change due to solar cycle variations is found.  相似文献   

11.
Gas concentrations and isotopic compositions of water have been measured in hydrothermal waters from 13°N on the East Pacific Rise. In the most Mg-depleted samples ( 5 × 10−3 moles/kg) the gas concentrations are: 3–4.5 × 10−5 cm3 STP/kg helium, 0.62–1.24 cm3 STP/kg CH4, 10.80–16.71 × 10−3 moles/kg CO2. The samples contain large quantities (95–126 cm3/kg) of H2 and some carbon monoxide (0.26–0.36 cm3/kg) which result from reaction with the titanium sampling bottles. δ13C in methane and CO2 (−16.6 to −19.5 and −4.1 to −5.5 respectively) indicate temperatures between 475 and 550°C, whereas δ13CCO is compatible with formation by reduction of CO2 on Ti at 350°C close to the sampling temperature.3He/4He are very homogeneous at (7.5 ± 0.1)RA(3He/4He = 1.0 × 10−5) and very similar to already published data as well as CH4/3He ratios between 1.4 and 2.1 × 106.18O and D in water show enrichments from 0.39 to 0.69‰ and from 0.62 to 1.49‰ respectively. These values correspond to W/R ratios of 0.4–7. The distinct18O enrichments indicate that the isotopic composition of the oceans is not completely buffered by the hydrothermal circulations. The3He-enthalpy relationship is discussed in terms of both hydrothermal heat flux and3He mantle flux.  相似文献   

12.
Centrifuge models simulating magma emplacement during oblique rifting   总被引：1，自引：0，他引：1  
A series of centrifuge analogue experiments have been performed to model the mechanics of continental oblique extension (in the range of 0° to 60°) in the presence of underplated magma at the base of the continental crust. The experiments reproduced the main characteristics of oblique rifting, such as (1) en-echelon arrangement of structures, (2) mean fault trends oblique to the extension vector, (3) strain partitioning between different sets of faults and (4) fault dips higher than in purely normal faults (e.g. Tron, V., Brun, J.-P., 1991. Experiments on oblique rifting in brittle-ductile systems. Tectonophysics 188, 71–84). The model results show that the pattern of deformation is strongly controlled by the angle of obliquity (α), which determines the ratio between the shearing and stretching components of movement. For α35°, the deformation is partitioned between oblique-slip and normal faults, whereas for α45° a strain partitioning arises between oblique-slip and strike-slip faults. The experimental results show that for α35°, there is a strong coupling between deformation and the underplated magma: the presence of magma determines a strain localisation and a reduced strain partitioning; deformation, in turn, focuses magma emplacement. Magmatic chambers form in the core of lower crust domes with an oblique trend to the initial magma reservoir and, in some cases, an en-echelon arrangement. Typically, intrusions show an elongated shape with a high length/width ratio. In nature, this pattern is expected to result in magmatic and volcanic belts oblique to the rift axis and arranged en-echelon, in agreement with some selected natural examples of continental rifts (i.e. Main Ethiopian Rift) and oceanic ridges (i.e. Mohns and Reykjanes Ridges).  相似文献   

13.
Silica chimneys were discovered in 1985 at 86°W in the rift valley of the Galapagos Spreading Center at 2600 m depth (“Cauliflower Garden”). The inactive chimneys lack any sulfides and consist almost entirely of amorphous silica (up to 96 wt.% SiO2, opal-A); Fe and Mn oxides are minor constituents. Oxygen isotope data show that formation of the silica chimneys took place at temperatures between 32°C (+29.9‰ δ18O) and 42°C (+27.8‰ δ18O).Th/Udating reveals a maximum age of 1440 ± 300y. Amorphous silica solubility relations indicate that the silica chimneys were formed by conductive cooling of pure hydrothermal fluids or by conductive cooling of a fluid/seawater mixture. Assuming equilibrium with quartz at 500 bars, initial fluid temperatures of more than 175°C (i.e., a concentration of > 182 ppm SiO2) were required to achieve sufficient supersaturation for the deposition of amorphous silica at 40°C and 260 bars. If the silica chimneys originate from the same or a similar fluid as higher-temperature ( < 300°C) sulfide-silica precipitates found nearby (i.e., 2.5 km away), then subsurface deposition of sulfides may have occurred.  相似文献   

14.
A numerical model of deep, uniform, oscillatory, rough-turbulent boundary-layer flow is described. The model is based upon the governing horizontal momentum equation and a closure scheme involving the turbulent-energy equation and various turbulence-scaling laws. Finite difference solutions of these equations are obtained for a range of values of the ‘relative roughness’ (A0/ks), whereA0 is the excursion amplitude of the water particles in the free-stream flow andks is the ‘equivalent bed roughness’. Typical vertical profiles of horizontal velocity, turbulence energy and eddy viscosity, and time-series of the bed shear stress are presented. The model results are then used to determine the wave drag coefficient, boundary-layer thickness and phase lead of the bed shear stress over the free-stream velocity, each as a function ofA0/ks. These results are shown to be in generally good agreement with previous experimental and theoretical results. Finally, the model is used to test for the existence of a universal velocity distribution for uniform oscillatory (sinusoidal) rough-turbulent flow. The ‘law of the wall’ and the ‘defect law’ proposed by Jonsson (1980, Ocean Engineering, 7, 109–152) are well supported by the model, and the existence of a logarithmic ‘velocity overlap layer’ in which both of these laws are valid is demonstrated forAo/ks30.  相似文献   

15.
According to the results of cyclic triaxial tests on Hangzhou sands, a correlation is presented between liquefaction resistance and elastic shear modulus. Material-dependent but independent of confining stress, shows the linear relation of (σd/2)1/2 with Gmax. For its application to different soils, a method proposed by Tokimatsu [Tokimatsu K, Uchida A. Correlation between liquefaction resistance and shear wave velocity. Soils Found 1990:30(2):33–42] is utilized to normalize the shear modulus with respect to minimum void ratio. A simplified equation is established to evaluate the liquefaction potential by shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the peak horizontal ground surface acceleration during earthquakes. The equation proposed in this paper is compared with previous methods especially the procedure proposed by Andrus [RD Andrus, KH Stokoe. Liquefaction resistance of soils from shear-wave velocity. J Geotech Geoenviron Eng 2000:126(11):1015–25]. The results show its simplicity and effectiveness when applied to sands, but more validation or modification is needed for its application to sand with higher fines content.  相似文献   

16.
Pressure–volume–temperature relations have been measured to 32 GPa and 2073 K for natural magnesite (Mg0.975Fe0.015Mn0.006Ca0.004CO3) using synchrotron X-ray diffraction with a multianvil apparatus at the SPring-8 facility. A least-squares fit of the room-temperature compression data to a third-order Birch–Murnaghan equation of state (EOS) yielded K0 = 97.1 ± 0.5 GPa and K′ = 5.44 ± 0.07, with fixed V0 = 279.55 ± 0.02 Å3. Further analysis of the high-temperature compression data yielded the temperature derivative of the bulk modulus (∂KT/∂T)P = −0.013 ± 0.001 GPa/K and zero-pressure thermal expansion α = a0 + a1T with a0 = 4.03 (7) × 10−5 K−1 and a1 = 0.49 (10) × 10−8 K−2. The Anderson–Grüneisen parameter is estimated to be δT = 3.3. The analysis of axial compressibility and thermal expansivity indicates that the c-axis is over three times more compressible (KTc = 47 ± 1 GPa) than the a-axis (KTc = 157 ± 1 GPa), whereas the thermal expansion of the c-axis (a0 = 6.8 (2) × 10−5 K−1 and a1 = 2.2 (4) × 10−8 K−2) is greater than that of the a-axis (a0 = 2.7 (4) × 10−5 K−1 and a1 = −0.2 (2) × 10−8 K−2). The present thermal EOS enables us to accurately calculate the density of magnesite to the deep mantle conditions. Decarbonation of a subducting oceanic crust containing 2 wt.% magnesite would result in a 0.6% density reduction at 30 GPa and 1273 K. Using the new EOS parameters we performed thermodynamic calculations for magnesite decarbonation reactions at pressures to 20 GPa. We also estimated stability of magnesite-bearing assemblages in the lower mantle.  相似文献   

17.
Basic properties of the mid-latitude traveling ionospheric disturbances (TIDs) during the maximum phase of a major magnetic storm of 6–8 April 2000 are shown. Total electron content (TEC) variations were studied by using data from GPS receivers located in Russia and Central Asia. The nightglow response to this storm at mesopause and termospheric altitudes was also measured by optical instruments FENIX located at the observatory of the Institute of Solar-Terrestrial Physics (51.9°N,103.0°E), and MORTI located at the observatory of the Institute of Ionosphere (43.2°N, 77.0°E). Observations of the O (557.7 and 630.0 nm) emissions originating from atmospheric layers centered at altitudes of 90 and 250 km were carried out at Irkutsk and of the O2(b1∑g+−X3∑g−) (0-1) emission originating from an atmospheric layer centered at altitude of 94 km was carried out at Almaty. Our radio and optical measurement network observed a storm-induced solitary large-scale wave with duration of 1 h and a wave front width of no less than 5000 km, while it traveled equatorward with a velocity of 200 m/s from 62°N to 38°N geographic latitude. The TEC disturbance, basically displaying an electron content depression in the maximum of the F2 region, reveals a good correlation with growing nightglow emission, the temporal shift between the TEC and emission variation maxima being different for different altitudes. A comparison of the auroral oval parameters with dynamic spectra of TEC variations and optical 630 nm emissions in the frequency range 0.4–4 mHz (250–2500 s periods) showed that as the auroral oval expands into mid-latitudes, also does the region with a developed medium-sale and small-scale TEC structure.  相似文献   

18.
The use of regional attenuation in computing the local magnitude, ML, from strong motion data gathered at distances less than 100 km may lead to systematic underestimates approaching 0·5 magnitude units (Trifunac & Herak, Soil Dynamics and Earthquake Engineering, 1992, 18, 229-41). The use of the attenuation law Att(Δ), for example, with synthetic estimates of Wood-Anderson seismometer response, during the Loma Preita earthquake, leads to estimates of ML which agree with the surface wave and moment magnitudes, and which are essentially distance-independent.  相似文献   

19.
Empirical scaling equations for Fourier amplitude spectra of strong ground motion are used to describe A0 and τ in the assumed (high-frequency) shape of strong motion amplitudes: FS(φ) = A0e-πτφ. The res of computed A0 and τ with other related estimates of spectral amplitudes; (2) smooth decay of strong motion spectral amplitudes up to φ = 25 Hz, without an abrupt low-pass filtering of high frequecies; and (3) good agreement with other estimates of the regionally specific attenuation of high-frequncy seismic waves.As the recorded strong earthquake shaking in the western United States typically samples only the shallow (10 km) and local (100km) characteristics of wave attenuation, the processed strong motion accelerograms can be used as the most direct means of describing the nature of the high-frequency attenuation of the entire strong motion signal for use in earthquake engineering applications. Seismological body wave, Lg and coda wave estimates of Q sample different volumes of the crust surrounding the station, and involve different paths of the waves. These differences must be carefully documented and understood before the results can be used in earthquake engineering characterization of strong motion amplitudes.  相似文献   

20.
First-arrival traveltimes from a multi-offset vertical seismic profile (VSP) were used to estimate velocity anisotropy in the presence of a vertical velocity gradient. A numerical model consisting of two layers with vertical velocity gradients of 3.1 and 1.2 s−1, respectively, and global anisotropy parameters of =0.12±0.02 and δ=0.30±0.06 yielded first-arrival traveltimes that matched the observed traveltimes well. Shallow receivers were found to be crucial for constraining the vertical velocity field and for determining the parameters of anisotropy at depth.  相似文献   

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