摘要:

We test the relation k = (m2/k0)F−1.5, where k is permeability, m is hydraulic radius, F is the formation factor, and k0is a constant close to 2.5. Parameters k, m, and F have been measured in the laboratory or taken from the literature for two granites and a number of sandstones and ceramics. Predicted and measured k agree to within about a factor of 2 over the 9 orders of magnitude range of k. A similar relation closely predicts the change in permeability with stress measured for granite. Application to rocks at depth seems limited at present, for although deep resistivity may be known, information on the size of pore spaces, needed to calculate m, is generally not availabl

ISSN:0148-0227    

DOI:10.1029/JB082i023p03343

年代:1977

数据来源: WILEY

摘要:

One hundred sixty‐four (164) high‐frequency Pnphases and 126 high‐frequency Snphases recorded on a short‐period seismograph temporarily operated at Ponape are used to complement and extend prior investigations of the Western Pacific mantle. Pnand Snphases are well recorded out to distances of 20° for moderate‐sized earthquakes (Mb≃ 5) for travel paths entirely within the relatively homogeneous geophysical provinces of the Northwestern Pacific Basin or the Ontong Java Plateau. For comparable events, Pnand Snphases are generally more prominent for travel paths in the Northwestern Pacific Basin than in the Ontong Java Plateau. Pnand Snpropagation is much less efficient but still possible for travel paths that cross island arc‐trench systems or island chains. For distances beyond 20°, Pnand Snare observed only for large earthquakes (Mb≥ 6.0) or for moderate‐sized earthquakes having substantial focal depths (>200 km). At all distances, Pnis generally more prominent on the seismograms than Sn. The maximum distance at which Pnand Snphases are recorded is 37.84° (4208 km). Snvelocities for the Northwestern Pacific Basin (>130 m.y. old) and for the Ontong Java Plateau (60 to 130 m.y. old) are 4.77±0.03 km/s and 4.70±0.07 km/s, respectively. Corresponding velocities for Pnare 8.33±0.05 km/s and 8.52±0.14 km/s. A suggestion of more than one Pn, Snwave guide is provided by Pnphases at distances in excess of 30°. The Pnvelocity for these

ISSN:0148-0227    

DOI:10.1029/JB082i023p03350

年代:1977

数据来源: WILEY

摘要:

The most precise measurements of strain on long base lines (1–11 km) are currently being made in central California near Hollister. Base lines radiating from Hollister have been measured daily, except when measurements are limited by poor visibility, since September 1975. Strain episodes have been observed that are attributed to slip at depth on the major faults in the area. There is a suggestion that this slip begins several kilometers down and propagates upward to the surface. Many of these strain episodes have coincided with magnitude 2.5–3.5 earthquakes in the region. Another strain episode indicates that the eastern end of the Sargent Fault may continue past the Calaveras Fault for approximately 2

ISSN:0148-0227    

DOI:10.1029/JB082i023p03361

年代:1977

数据来源: WILEY

摘要:

Results of four leveling surveys carried out by the National Geodetic Survey between Anchorage and Whittier, Alaska, combined with an analysis of sea level measurements at Anchorage, indicate as much as 0.55 m of land uplift in the decade following the 1964 Prince William Sound earthquake. The pattern of uplift is parabolic in shape, convex upward, and reaches a maximum approximately halfway between Anchorage and Whittier, or about 300 km northwest of the Aleutian trench axis. The data suggest that the position of maximum uplift is migrating away from Anchorage, i.e., toward the Aleutian trench. The observed uplift occurs in a region which subsided as much as 1.9 m during the earthquake. The rate of uplift has decreased exponentially since the time of the 1964 earthquake. These movements appear to represent postseismic deformation associated with the 1964 Alaska earthquake. The observations are most easily explained by creep along the downdip extension of the fault which ruptured during the 1964 earthquake, although viscoelastic rebound and long‐term elastic strain accumulation mechanisms may play a part. There is no evidence supporting magma intrusion or dilatancy mechanisms. These results provide new constraints for models of tectonic processes at convergent plate margin

ISSN:0148-0227    

DOI:10.1029/JB082i023p03369

年代:1977

数据来源: WILEY

摘要:

Appreciable changes in elevations of satellite tracks create significant highs, lows, and trends in a map of the residual total magnetic field. In order to remove these features associated with the peculiarities of the satellite path a method has been developed to reduce the observed residual field to a spherical surface at a constant height from the ground. The reduced field is then continued downward to a parallel surface with recursive operators for enhancement of the detailed features of the anomalous field. The residual field obtained by the process of downward continuation is nonharmonic owing to the variation of the direction of the geomagnetic field over the large area usually covered by satellite anomalies. For this reason the components of the field along fixed directions in space are calculated from the residual total field by employing a new method. This method provides expressions for the field components in the form of digital convolutions of the residual field with suitable operators. The components can then be combined, if necessary, to produce the anomalous total field at any fixed geomagnetic latitude.

ISSN:0148-0227    

DOI:10.1029/JB082i023p03379

年代:1977

数据来源: WILEY

摘要:

We present 206 new heat flow measurements in the Indian Ocean. These and approximately 300 previously published heat flow values are individually evaluated for sedimentary environment and instrumental performance. The relationship between average heat flow and age is found to be little affected by selection of the most reliable experiments, although the scatter about the mean is significantly lowered. The variation of mean heat flow with age is found to be very similar to that in the eastern Pacific and Atlantic oceans: There is a crestal low heat flow zone with large variability, a transition zone within which the heat flow increases from values considerably below to values in agreement with predictions from thermal models of the oceanic lithosphere, and a region where heat flow values are in accord with theoretical predictions. However, the transition zone occurs over different crustal ages from ocean to ocean: 40–60 m.y. in the Indian Ocean, 4–6 m.y. in the Galápagos spreading center, 10–15 m.y. on the East Pacific Rise, and 50–70 m.y. on the Mid‐Atlantic Ridge. The transition zone generally corresponds to a sea floor age where (1) sedimentary thickness increases to ≥300 m, (2) sea floor roughness is significantly smoothed by sediment blanketing, and (3) the carbonate content of surface sediments decreases to ≤40%. The transition zone occurs where water circulation in the oceanic crust stops affecting the surface heat flow strongly. There are two possible explanations for the transition. First, a change in composition from carbonate to siliceous sediments results in a decrease in bulk permeability. This combined with general thickening of the sedimentary blanket with aging results in the deposition of an impermeable layer which prevents the convective exchange of heat from the oceanic crust to the ocean. Second, hydrothermal flow within the oceanic crust is plugged by filling of circulation cracks in the oceanic crust. The fact that in several basins of the Indian Ocean the heat flow transition corresponds with the carbonatesiliceous boundary is support for the former mechanism. However, the fact that locations of increases in velocity of seismic layer 2A generally correspond to the transition regions in the Atlantic and Pacific oceans provides support for the latter mechanism. Heat flow measurements in the world's oceans allow us to calculate the variations of bulk permeability and basal temperature in the oceanic crust as a function of age and to evaluate the geochemical implications of the variation in these parameters between oceans. The combination of conductive heat flow and elevation versus age observations in old lithosphere demonstrates the deviation fromt1/2cooling in the Indian Ocean and indicates that the Mozambique and western Somali basins are considerably older than preliminary deep‐sea drilling results suggest.1 Supplementary table is available with entire article on microfiche. Order from American Geophysical Union, Suite 1000, 1909 K Street, N.W., Washington, D.C. 20006. Document J77‐003; $1.00. Payment mu

ISSN:0148-0227    

DOI:10.1029/JB082i023p03391

年代:1977

数据来源: WILEY

摘要:

The conditions for the onset of convection and the characteristics of the convection at the onset of instability are determined for a porous medium containing either a saturated liquid or a steam‐water mixture. Convection is driven by a phase change instability mechanism. If steam and water are always in thermodynamic equilibrium, then temperature perturbations are directly responsible for pressure variations, which tend to move the fluid against the frictional resistance of the medium to flow. Mass conservation insures that any horizontal divergence of fluid is balanced by an appropriate vertical motion, while condensation and boiling occur to achieve a balance of forces in the vertical. Convection occurs more readily in a porous medium containing saturated liquid by the phase change instability than it would in a porous layer filled with ordinary water by the Rayleigh‐Bénard buoyancy‐driven instability. Porous layers with steam‐water mixtures are also more susceptible to convection than are those containing ordinary water. Phase‐change‐driven convection is concentrated toward the bottom of the porous layer; the cells are narrow in comparison to

ISSN:0148-0227    

DOI:10.1029/JB082i023p03411

年代:1977

数据来源: WILEY

摘要:

In an earlier paper by the authors (Peale and Boss, 1977), rather severe constraints were placed on the properties of a Mercurian liquid core and certain other dynamical characteristics of the planet for consistency with Mercury's escape from the spin‐orbit resonance with the spin angular velocity equal to twice the orbital mean motion. One assumption under which these constraints were established was that the obliquity θ ≈ 0 at the time of resonance passage. Here we show that for θ ≠ 0, Mercury can easily escape the spin resonance with a large core of low viscosity, and all constraints established for resonance passage for θ = 0 would vanish. However, the same effect which so drastically reduces the probability of capture into the 2nresonance also would have reduced θ to negligibly small values long before the 2nresonance was reached. Thus Mercury most likely passed through ΨM= 2nwith θ ≈ 0, and hence the previously established constraints of the kinematic viscosity ν ≈ 0.01 and the tidal dissipation factorQ≲ 100 for a laminar core‐mantle boundary layer and the constraints on critical Reynolds numberRc≳ 500, tidalQ≲ 40, and moment differences (B‐A)/C≲ 10−5for a turbulent boundary layer are still applicable for any core capable of dynamo

ISSN:0148-0227    

DOI:10.1029/JB082i023p03423

年代:1977

数据来源: WILEY

摘要:

26Al (dpm/kg) and or He, Ne, and Ar have been measured in samples of the Norton County meteorite from three different depths. The gas contents yield a shielding‐corrected age of 75.8±5.7 m.y. The ratio of atomic production rates P(26Al )/P(21Ne) is 0.22±0.02.3He,21Ne, and26Al increase with decreasing22Ne/21Ne at nearly the same rates as they do in the smaller Keyes chondrite.26Al contents were measured in Bustee (75.9±3.3), Khor Temiki (89.9±3.5), Pesyanoe (98.4±3.4), and Shallowater (62.8±2.0) meteorites.26Al/26Alocorrelates with22Ne/21Ne, and comparison with the corresponding chondrite correlation indicates that the aubrites, like Malakal, may have experienced an unusually high flux of cosm

ISSN:0148-0227    

DOI:10.1029/JB082i023p03430

年代:1977

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JB082i023p03437

年代:1977

数据来源: WILEY