摘要:

Tidal water‐level fluctuations were recorded in ten observation wells in Virginia. Six wells are located on the Atlantic coastal plain, and four are in the Appalachian mountain region. A quantitative explanation of the observed well tides is developed from consideration of the tidal dilatation of an idealized well‐aquifer system. The response of a confined well‐aquifer system to tidal dilatations requires consideration of the earth tidal dilatation ΔE, the barometric tidal dilatation ΔB, and the ocean tide dilatation Δoaccording to the equation:ΔA=‐ρg dh(1‐nEM+nEW)where ρ is fluid density,gis gravitational acceleration,dhis the height of the well tide,nis porosity,EMis the bulk modulus of the aquifer matrix, andEWis the fluid bulk modulus. The aquifer dilatation ΔAis given by the expressionΔA=(ΔE+ΔBcosϕB+Δocosϕo)/cosϕAwhere ϕB, ϕo, and ϕAare phase differences between the tide‐generating potential and the barometric tide, ocean tide, and well tide, respectively. For wells located far inland Δocan be neglected. For wells located near the ocean the explanation of tides requires analysis of at least two tidal harmonic constituents and the ratio of the heights of the corresponding ocean tide constituents. In this situation the above equation can be written simultaneously for two tidal harmonic constituents. The magnitudes of the ocean tide dilatations can be eliminated in solving the simultaneous equations, but their ratio must be known. Calculation of aquifer porosity from well tide analysis is restricted by uncertainty about bulk modulus and ocean loading effects. If a well‐aquifer system is located far enough inland so that ocean tide effects can be neglected, porosity values can be obtained to an accuracy subjectively estimated at ±5 percentage points. Specific storage capacity of a well‐aquifer system can be more accurately calculated than porosity because independent estimates of a

ISSN:0148-0227    

DOI:10.1029/JB076i008p01857

年代:1971

数据来源: WILEY

摘要:

The melting gradient and the adiabatic gradient throughout the core of the earth are compared. The temperature of melting of iron at pressures equivalent to the inner core‐outer core boundary is estimated to be circa 4250°C with a melting point gradient of approximately 500° through the outer core. The adiabatic gradient through the outer core is estimated to be circa 1250°; therefore, for the outer core to be liquid, its temperature must be considerably above the temperature in adiabatic equilibrium with the inner‐outer core boundary. The temperature distribution throughout the outer core is deduced to follow a melting point curve. This temperature distribution should provide a substantial inhibition to radial components of convection in the oute

ISSN:0148-0227    

DOI:10.1029/JB076i008p01870

年代:1971

数据来源: WILEY

摘要:

The results of a metallographic and electron microprobe study of the metal phases in five reheated chondrites are reported. The meteorites studied were reheated by shock to residual temperatures ranging from 480°C up to about 1200°C. These temperatures correspond to shock pressures ranging from 0.5 to>0.8 Mb. In two cases the metal was essentially homogenized by solid‐state diffusion; in two others the metal‐troilite assemblage was clearly melted. The phosphorus content of the metal phase was found to be substantially higher than in unreheated ordinary chondrites. It was concluded that the phosphorus was reduced from calcium phosphate by carbon; the reduction was made possible by the stabilization of phosphorus either by dissolution in the metal phase or by the formation of phosphides. Using the known coefficients of Ni diffusion in the metal phase and the temperature‐time dependence in the center of a semi‐infinite slab of finite thickness, the maximum depths at which these meteorites were buried after the shock events were estimated. The values ranged from less than one meter up to several hundr

ISSN:0148-0227    

DOI:10.1029/JB076i008p01879

年代:1971

数据来源: WILEY

摘要:

Gravity fields in Afghanistan are characterized by large, negative mean free‐air anomalies in the eastern Hindu Kush and by essentially zero anomalies in the western Hindu Kush. Thus, the western Hindu Kush are in isostatic equilibrium, whereas the eastern Hindu Kush are associated with a large mass deficiency. A mechanism involving underthrusting of light continental crust into higher density mantle in the eastern Hindu Kush and Pamirs is consistent with regional seismicity and gravity fields. Positive free‐air and Bouguer anomalies mark a belt of intrusives that occupy a region of northeast‐striking fractures along the Chaman fault zone. This zone may represent the northwest border of the Indian subcontinental

ISSN:0148-0227    

DOI:10.1029/JB076i008p01894

年代:1971

数据来源: WILEY

摘要:

A new analytical method of representing irregular surfaces that involves the summation of equations of quadric surfaces having unknown coefficients is described. The quadric surfaces are located at significant points throughout the region to be mapped. Procedures are given for solving multiquadric equations of topography that are based on coordinate data. Contoured multiquadric surfaces are compared with topography and other irregular surfaces from which the multiquadric equation was derived.

ISSN:0148-0227    

DOI:10.1029/JB076i008p01905

年代:1971

数据来源: WILEY

摘要:

The matrixC−1An, whereAis a square non‐singular matrix with real coefficients,na positive integer, andCthe triangular matrix resulting from the Cholesky factorizationAn(An)T=CCT, is orthogonal and a convergent to the orthogonal matrixXfor whichXAX−1is triangular. This matrix can be computed to any desired degree of precision by iteration. For symmetricA, (A=AT),Xis the modal matrix (matrix of unit eigenvectors) and the convergence is considerably accele

ISSN:0148-0227    

DOI:10.1029/JB076i008p01916

年代:1971

数据来源: WILEY

摘要:

The problem of ground wave propagation over a nonuniform overburden with arbitrarily varying complex dielectric coefficient and depth is analyzed. Using a full wave approach, the effects of the nonuniform overburden upon the surface wave and the radiation field are examined. The criteria for distinguishing between the effects of variations of the overburden depth and variations of its complex dielectric coefficient are determined. In particular, the feasibility of using radio‐wave measurements to map the water table and the overburden conductivity is explore

ISSN:0148-0227    

DOI:10.1029/JB076i008p01921

年代:1971

数据来源: WILEY

摘要:

A crustal refraction experiment was carried out around Yellowknife, Northwest Territories, in 1966. The pattern of shots and stations was designed for time‐term interpretation over a wide area, traversed by a more detailed line of interspersed shots and stations. The records were unusually simple, and nearly all arrival could be explained by a shallow surface layer (3.5±1.2 km at 5.5 km/sec) overlying a uniform crust (6.1±0.04 km/sec). No significant difference was found between the crustal thicknesses under the Slave and Churchill Precambrian provinces, but they are separated by a narrow belt corresponding to the east arm of Great Slave Lake, under which the crust is about 4 km thicker. The structural interpretation is supported by a study of the amplitudes ofPn. The upper mantle velocity west of the Precambrian margin (8.23±0.04 km/sec) was found to be higher than that east of the margin (8.10±0.03 km/sec). This may be related to an orogenic belt parallel to but west of the margin in late Aphebian

ISSN:0148-0227    

DOI:10.1029/JB076i008p01929

年代:1971

数据来源: WILEY

摘要:

A bathymetric and magnetic profile along 143°W from 29°N to 50°N crosses the Murray, Pioneer, Mendocino, Surveyor, and Sedna fracture zones at nearly right angles and serves to locate several of these features in an area where they previously were known only generally. A large leveed channel, probably Mukluk channel, lies atop a broad turbidite deposit between the Surveyor and Sedna fracture zon

ISSN:0148-0227    

DOI:10.1029/JB076i008p01948

年代:1971

数据来源: WILEY

摘要:

The movements of crustal blocks in the new global tectonics can be described in terms of edge dislocations flowing along a transform fault. The dislocations are created at the oceanic ridges and absorbed at the oceanic trenches, but along the transform fault they are conserved. The total creep strain rate across the fault zone at any point on the transform fault will be proportional toq, the flow of dislocations past that point. A simple physical model of fault creep suggests thatq=q(k,x,k′), wherekis the concentration of dislocations per unit length of fault,xis the position coordinate measured along the fault length, andk′ is the gradient ofk. Thus, the flowqis governed by a kinematic wave equation. The propagation of kinematic waves is characterized by amplitude dispersion that leads to the formation of propagating shock waves, i.e. abrupt changes in the creep rate. The model suggests that the arrival of these shock waves, which presumably is connected with high earthquake hazard, might be forecast in much the same way as flood crests on river systems are now predicted. The very large earthquakes along the transform‐fault system that bounds the west coast of North America exhibit a migration pattern suggesting kinematic shock propagation. A similar pattern has been observed along the Anatolian

ISSN:0148-0227    

DOI:10.1029/JB076i008p01954

年代:1971

数据来源: WILEY