摘要:

A single closed expression is derived for the product‐sum conversion of spherical harmonics and their derivatives to any order. The equations for thermal convection in a sphere at an infinite Prandtl number are transformed to a set of quadratic first‐order ordinary differential equations suitable for numerical integration with respect to radius. The product‐sum formulas are applied to the quadratic terms arising from advection, dissipation, and the linear temperature dependence of visc

ISSN:0148-0227    

DOI:10.1029/JB080i002p00225

年代:1975

数据来源: WILEY

摘要:

Current interpretations of heat flow values within the framework of plate tectonics concepts fail to reproduce the available observations for the oceanic ridge crests and give heat flow singularities. A new mathematically tractable theory of vertical intrusion (using a non‐uniform temperature distribution at the ridge crest) has been constructed that shows a reasonable fit between predicted and observed heat flows. In this theory the derived heat flow is finite everywhere. It should serve as a useful starting point in the inverse problem of deriving the temperature distribution with depth on the basis of surface evidence. The plate model currently used assumes vertical intrusion at a uniform temperature to create crust at the oceanic ridges. This simple model does predict such features as the topography and the high heat flow in the ridge crest areas, but it has some deficiencies, including a discrepancy between observed and theoretical heat flow profiles; in particular, the model predicts infinite heat flow in the narrow zone where new lithosphère originates, so that the predicted relationship between the lithospheric thickness and the heat flow half width is valid only far away from the ridge axis. Previous models give rise to infinite heat losses, and the lithospheric thickness is a free parameter not determined by the physics of the problem. In this paper we introduce a new model that overcomes the difficulties involved in previous models. A new parameter is involved, which we interpret physically as the level of hot solid material above the melt column going from the bottom of the lithosphere. Observed data on maximum heat flow values at the ridge crest are used to determine this parameter. The lithospheric thickness in a given region can be determined by the way in which the heat flow decreases along the ridge flanks. Heat losses for the oceanic ridges are calculated in our nonsingular model by separating out the anomalous two‐dimensional part of the temperature and heat flow field. Thus a heat loss for ocean ridges amounting to 0.2–0.3 of the global heat loss is

ISSN:0148-0227    

DOI:10.1029/JB080i002p00232

年代:1975

数据来源: WILEY

摘要:

The main interaction of the interior with the lithosphere is as a material source and sink. An absolute reference frame defined by minimizing the translational motion of tectonic plate boundaries differs by 0.6 cm/yr from a frame defined by hot spot traces and by 0.4 cm/yr from the frame defined by the most plausible model of drag forces on the plates. The rms absolute translational velocities are about 2 cm/yr for ocean‐ocean plate boundaries and 1 1/2 cm/yr for ocean‐continent plate boundaries. The close agreement between the source and sink and the drag‐dependent definitions suggests that the lithosphere, as a stress guide, to some extent controls the locations of its sources and

ISSN:0148-0227    

DOI:10.1029/JB080i002p00244

年代:1975

数据来源: WILEY

摘要:

The Lomnitz and Futterman theories of internal friction are shown to be so similar that experimental distinction between the two is unlikely at present. The Futterman theory is largely ad hoc, and for this reason the Lomnitz theory should be preferred. Both theories require that a measurable amount of dispersion accompany attenuation. In fact, the detection of the proper amount of dispersion is crucial in demonstrating that any linear theory can explain the observed attenuation. Wuenschel has detected dispersion of the correct amount in in situ experiments in the Pierre shale and laboratory experiments in Plexiglas, but O'Brien and Lucas have failed to detect any significant dispersion in a statistical compilation of a large number of oil well logs.

ISSN:0148-0227    

DOI:10.1029/JB080i002p00249

年代:1975

数据来源: WILEY

摘要:

Theoretical examination of possible nonuniform spin configurations in metallic iron indicates that circular spin (CS) is the lowest‐energy nonuniform arrangement. The upper grain size limit (d0) to single‐domain (SD) behavior is thus defined by the SD to CS transition. Superparamagnetic (SP) behavior marks the lower grain size limit to the stable SD range, and the SP to SD threshold size (ds) can be determined by Néel's relaxation theory. Calculations ofd0anddsfor spherical metallic iron particles at 290°K indicate thatd0( = 173 Å)1.1 but remains very constricted. For a prolate ellipsoid ofq= 1.67, a stable SD range occurs between the SP critical length LS= 150 Å andd0= 360 Å. Bothd0anddsincrease with temperature, but the stable SD range decreases. The size and shape criteria for the stable SD behavior of metallic iron help to explain (1) the low SD content of lunar samples, (2) the widespread occurrence of SP behavior and viscous magnetization in lunar soils and low metamorphic grade breccias, (3) the changes in the magnetic properties of breccias during annealing, and (4) the increased SD content of shocked breccias. The narrow grain size limits for SD behavior also suggest that magnetostatic interaction between metal grains in the solar nebula is not a viable mechanism for iron‐silicate fr

ISSN:0148-0227    

DOI:10.1029/JB080i002p00252

年代:1975

数据来源: WILEY

摘要:

The patterns of seismic activity before large strike slip and thrust‐type earthquakes were examined for intervals as great as 45 years before the main shocks. The earthquakes chosen for this investigation occurred along the northwestern, northern, and eastern margins of the Pacific, and most of these events had rupture zones that extended hundreds of kilometers. The observed distribution of prior seismicity for these earthquakes correlates with the configurations of their rupture zones and with the epicentral locations of the main shocks within the zones. An obvious and consistent feature of these spatial distributions is the relatively aseismic character of extensive portions of the rupture zones until the times of the main shocks. These reduced levels of seismic activity extended to events at least several magnitudes smaller than the main shocks and possibly many magnitudes smaller. For most of the large earthquakes examined, rupture initiated in an area of moderate seismic activity and then propagated as much as hundreds of kilometers into adjacent quiet regions. In at least several instances, rupture also terminated in a region of some prior activity. Thus prior seismicity frequently occurred near the epicenters of the main shocks and/or near the edges of the rupture zone. There are some indications that the level of this prior activity, particularly in the vicinity of the epicenter, increased as the time of the main shocks approached. Thus one important conclusion of this study is that gaps in seismicity for great earthquakes along major plate boundaries may also be gaps for smaller‐magnitude activity. Further, such gaps may commonly remain so until the time of the principal shock. That is, if premonitory activity is associated with large earthquakes, such activity should be sought along the boundaries of a seismic gap rather than in the gap itself. Along the great transform fault system near western Canada and southeastern Alaska the nature of the seismicity varies noticeably with distance northwest of the Juan de Fuca spreading center. That is, the area near the spreading center is a region of frequent moderate‐sized earthquakes (M= 6); further north is a region of occasional large earthquakes (M= 7); even further north is a region of infrequent great earthquakes (M= 8). This changing seismic regime is similar to that of the San Andreas system proceeding north from the spreading centers in the Gulf of California. Along both transform fault systems, and possibly others, the change in characteristic seismicity may be a function of the changing lithospheric structure with distance from the spreading centers.Data are available with entire article on microfiche. Order from American Geophysical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document J75‐001; $1.00. Payment must accompan

ISSN:0148-0227    

DOI:10.1029/JB080i002p00260

年代:1975

数据来源: WILEY

摘要:

Rotation of the compressive stress axis associated with the focal mechanism of a seismic event has been found to precede several large thrust earthquakes in the Garm region of the USSR. A possible explanation can be offered by assuming systematic vertical migration of foreshock activity within a region of thrust tectonics. Some laboratory and other results appear to support this possibility.

ISSN:0148-0227    

DOI:10.1029/JB080i002p00272

年代:1975

数据来源: WILEY

摘要:

The thermoelastic effects of a traveling wave of temperature on the surface of an infinite homogeneous elastic half space are examined. The horizontal and shear strain and the tilt are principally caused by tractions in the thermal boundary layer, and they decay vertically with the scale of the horizontal wavelength of the applied temperature wave. The vertical strain is larger at the surface by the ratio of this wavelength to the thermal boundary thickness, but below the boundary layer it behaves like the other components. The burial of instruments at practical depths is unlikely to reduce significantly the thermoelastic effects except on the vertical strain.

ISSN:0148-0227    

DOI:10.1029/JB080i002p00274

年代:1975

数据来源: WILEY

摘要:

A necessary condition for the generation of magnetic fields by fluid motions in a sphere is derived in terms of the magnetic Reynolds number on the basis of the radial component of the velocity field. A second parameter entering the criterion is the ratio between the energy of the poloidal component of the magnetic field and the total magnetic energy. Since bounds on this ratio can be obtained from energetic considerations, the criterion can be used as a restriction on possible dynamo mechanisms. Several recent suggestions for the origin of the geodynamo in a stratified outer core are critically reviewed.

ISSN:0148-0227    

DOI:10.1029/JB080i002p00278

年代:1975

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JB080i002p00281

年代:1975

数据来源: WILEY