Pure and Applied Geophysics

Stacey, Frank

doi: 10.1007/BF00879136pmid: N/A

Local variations in the geomagnetic field, which are produced by stress changes in crustal rocks, are calculable from the stress patterns and the piezomagnetic properties of the rocks down to the Curie point isotherm. Release of stress during movement along a section of a transcurrent fault at an angle ϕ, measured clockwise with respect to the direction of magnetization of the rocks, produces a change in field similar to that which would be produced by the addition of a buried dipole of orientation (2ϕ±π/2), the alternative signs applying to right- and left-lateral faults. Computed seismomagnetic anomalies of horizontal, vertical and total field are plotted for different fault orientations in simple geological environments. Time-dependent magnetic anomalies with magnitudes of the order 10 gammas may commonly accompany the build-up of stress before an earthquake and provide a pre-indication of it.

Maaz, Richard

doi: 10.1007/BF00879137pmid: N/A

—Als Modell eines mechanischen Empfängers, der im Boden eingebettet ist, dient eine Kugelschale mit lineartranslatorisch beweglichem Gehänge. Das umgebende Medium erfüllt homogen den Vollraum und ist isotrop elastisch. Der Kontakt mit dem eingebetteten System wird entweder als haftend oder gleitend vorausgesetzt. Es ist diskutiert worden, wie sich der Empfänger in einer longitudinalen Planwelle von beliebiger Wellenform bewegt, die sich parallel zur Gehängetranslation ausbreitet. Ferner wurde die (unbekannte) Wellenform aus der Seismogrammform oder der Gestellbewegung explizit berechnet. Es ergeben sich beachtliche mathematische und physikalische Vereinfachungen, wenn das Gehänge vernachlässigbar leicht und die Gestellmasse gleich der «verdrängten Mediummasse» ist. Schliesslich wird der Zusammenhang dieses Vorgangs mit der Empfängerbewegung infolge Kräften besprochen, die nicht von der Welle herrühren und am Gestell und Gehänge gleichzeitig angreifen können. Es wurde der Kraftverlauf gesucht, der einer vorgegebenen Wellenform hinsichtlich der erzwungenen Gestellbewegung (und des Seismogramms) gleichwertig ist, und umgekehrt die zu einer bestimmten Kraftfunktion äquivalente Wellenform angegeben.

Sarkar, Gopi

doi: 10.1007/BF00879138pmid: N/A

It has been noted by several observers that no Love-wave spectrum is complete in the sense that it contains all the periods. The reason for this has been sought for in the presence of a low-velocity layer.

Maulik, Tapendra

doi: 10.1007/BF00879139pmid: N/A

It has been found that when seismic energy propagates along the surface of the homogeneous crust beside usual Rayleigh waves, it produces certain instability in layers through which it propagates. In the light of this instability, a type of motion corresponding to longitudinal wave will be prominent in horizontal component compared to the vertical component; while transverse wave will be prominent in the vertical component but weak in the horizontal component, a contradiction with the existing knowledge. This has been identified withP F phase. On taking the medium of propagation as slightly heterogeneous which allows existence of low velocity layer, a few larger number of such instabilities have been found. Velocity equation for Rayleigh waves for such media reveals existence of different velocities corresponding to vertical and horizontal components. Table for these velocities has been furnished.

Gassmann, Fritz

doi: 10.1007/BF00879140pmid: N/A

Section 1 (and 11) develops the concepts of the front velocity, the front gradient, the travel time in space and on seismometric profiles, the profile velocity and the profile gradient in connection with the propagation of the fronts of elastic waves in solid isotropic and anisotropic media. The sectional velocity and the sectional gradient are defined in terms of the motion of the curve of intersection of a front with a fixed surface. Section 2 (and 12) relates the coefficients of elasticity of the medium, the front types, and their respective rays. In section 12, the theory of fronts of arbitrary shape and of the corresponding rays for any anisotropic, homogeneous or inhomogeneous solid medium is summarized. In section 3 (and 13), the law of reflection and refraction of fronts on surfaces of discontinuity of arbitrary shape is presented. Sections 4 to 6 (and 14 to 16) treat some elementary applications of seismic travel time methods to homogeneous, uniaxially anisotropic media (=transverse isotropy) in greater detail. In section 4 (and 14), the travel time of a direct front generated by a point source is considered and it is shown how the coefficients of elasticity of the medium can be found based on travel time measurements. The seismic prospection of a plane reflector and of a reflecting boundary of arbitrary shape and position are discussed in section 5 (and 15). In section 6 (and 16), the seismic refraction method is used to locate a plane boundary between a homogeneous, uniaxially anisotropic and a homogeneous isotropic medium, where the boundary is perpendicular or at an arbitrary angle to the direction of anisotropy.

Ochoa, Daniel; William Stauder, S.

doi: 10.1007/BF00879141pmid: N/A

The focal mechanisms of two Peruvian earthquakes, January 15, 1958, and January 13, 1960, are determined using data from both the first motion ofP and the polarization ofS. The fault motions correspond to strike slip motion on neighboring faults corresponding in strike to geophysical evidences of regional faulting. The motion is left lateral in one of the shocks, right lateral in the other.

Morgenstern, Norbert; Taylor-Smith, Denzil

doi: 10.1007/BF00879142pmid: N/A

During uniaxial compression of clay cylinders it was observed that the longitudinal velocity decreased as each load increment was applied and then increased under constant stress. It is suggested that the load increment induces an increase in pore water pressure thereby reducing the effective stress. The velocity is dependent upon the effective stress and it decreases accordingly. The velocity then increases due to the dissipation of the pore pressure.

Schellenberger, Günter

doi: 10.1007/BF00879143pmid: N/A

Unter der Annahme, dass die Koeffizienten der Entwicklung der Streufunktion nach Legendreschen Polynomen bekannt sind, wird die für grosse Tiefen eines trügen Mediums gültige Strahlungsintegralgleichung gelöst, indem die Lösung ebenfalls nach Legendreschen Polynomen entwickelt wird. Es wird gezeigt, dass die Koeffizienten dieser Entwicklung sich rekurrent berechnen lassen. Für das relative Unterlicht wird eine bei geringem Streuanteil gültige Näherungsgleichung abgeleitet, die nur die Koeffizienten der Entwicklung der Streufunktion nach Legendreschen Polynomen enthält.

Starr, Victor; Wallace, John

doi: 10.1007/BF00879144pmid: N/A

It is suggested on the basis of the study of observational data gathered byJ. P. Peixoto that the eddy processes in the tropical regions of the middle troposphere operate in an inverse manner as compared with a normal heat engine. Thus, in common with the situation in the lower stratosphere, the region is characterized by a countergradient horizontal eddy heat transport and a rising of colder air and sinking of warmer air on the scale of the large eddy processes.

Newell, Reginald

doi: 10.1007/BF00879145pmid: N/A

Two approaches are used to describe and distinguish between those regions of the atmosphere which most closely resemble heat engines and those which operate like refrigerators. Estimates of the conversion from eddy potential energy to mean zonal potential energy are presented as a function of height, latitude and season; the region of forced motion (or refrigerator) in the lower stratosphere appears to be closely related to the maximum westerly winds of the upper troposphere. A preliminary attempt is made to relate some values of mass transport derived from the observations of trace substances to the energy conversions.