ALBERT

Notizen: Using a comprehensive theory of the vertical force variometer, it is shown that the mean of the two readings taken in azimuths 180 degrees apart only eliminates the error of misorientation and of inclination of the knife edge if these factors are sufficiently small. The necessary accuracy in the 180 degree rotation and in the readjustment of the levels are investigated and a practical test is developed to allow the initial adjustments to be determined. Finally, a brief description of a new variometer tripod is given.

Notizen: It is known that good use can be made of calculating the second vertical derivative of gravitational and magnetic fields. The first derivative, or Vertical Gradient, has the same properties, Like the second derivative, it does not depend on the locally linear regional anomaly. Moreover, the gradient is less affected by experimental errors.The report gives a practical method of calculating the vertical gradient. Its application is identical to that in general use for calculating the second derivative, except that the numerical coefficients are different. The method also allows the establishment of formulae for downward extension of the field and its derivatives.

Notizen: In the region covered by the paper, electrical methods have been applied in four different zones:〈list xml:id="l1" style="custom"〉a) Ales-Maruejols Basin (resistive lower Oligocene blanketed by conductive Upper Oligocene);b) Ledignan and Vaunage-Lunel anticlines (faulted structures in the marly and limy Cretaceous, with different resistivities;c) Camargue (thick series of conductive sediments);d) Beziers Basin (highly complicated structures in the Mesozoic, widely blanketed by conductive Miocene).It may be assumed that electrical methods can yield valuable information enabling one to define the rugged subsurface topography of resistive strata burried under a reasonably thick cover of conductive sediments especially when a part of the lower formation outcrops even if the part exposed be small. Faults may be delineated and much, more information is obtainable than can be expected from gravity meter survey at a price not very much higher.

Notizen: For the treatment of the problems involved in the interpretation of gravity pictures this paper gives a formula that holds generally for any potential function. It provides an extended applicability of the relation used by Elkins for the computation of the second derivative, and also yields an analogous relation to derivatives of higher order of the gravity field.This relation has not been utilized to determine in details the course of the derivatives of higher order in a plane, but is merely applied to points of comparatively extreme curvature of the isogams where the differential values present a ratio favourable to the “noise level”. By this method the values of the derivatives of higher order will not be determined themselves but only the ratio's responsible for the depth of divergence in comparison with the course of an anomaly of masses replaced by points.It is shown by examples of intercalated masses that the divergence points are important and by law related to the form and position of the density contrasts themselves.An analysis of the total gravity picture is made possible by progressing from elements close to the surface to deeper ones. In this way the fundamental features of the earth's crust will be obtained. The application of the analysis process to a gravity anomaly actually measured in Northwest Germany is given.

Notizen: When refraction time signals are transmitted over a radio link between shooter and observer there is a serious risk of interference from electrical storms. This risk can be minimised by sending a series of signals at fixed time intervals and the paper describes a simple device which will do this with the required accuracy.

Notizen: Seismic reflection, telluric and gravity results are given for the lifted area of Ferrara, in Northern Italy. The agreement is shown between the available shallow seismic data and the gravity evidences. For a portion of the above area where seismic results are particularly poor the vertical gradients method gives a resolution of a gravity anomaly and confirms the telluric information. The residual gravity values, the vertical gradients and the telluric data along a seismic line crossing the zone are compared with seismic results and with evidences from adjacent wells.

Notizen: Investigations into reflection seismic on the salt structure of Heide raised the following questions:〈list xml:id="l1" style="custom"〉1) How can the different directions of trend of a series of layers be established?2) How are the contour maps of reflecting horizons to be constructed if there is no general trend of the layers?To answer these questions, the case of the subsoil consisting of a series of layers with plane reflecting beds and constant layer-velocities is treated strictly. The strike lines of the reflecting planes may be at any angle whatever. However, formulas for constructing contour maps of the reflecting planes have been derived. With these formulas, the problem quoted under 1) has also been solved.The construction of contour maps is given.For special cases, formulas are obtained which have already been proved by others.

Notizen: The triple integral for the attraction of a mass on a point is transformed in a double sum. This double sum serves to construct a graph for the rapid determination of the gravimetric influence of structures given by depth contours. The influence of topography can also be computed with this graph.

Notizen: Supersonic pulses are transmitted into rock samples and cylindrical drill cores of about 10 cm to about 100 cm in length by a magnetostrictive driver attached to one end. The pulses are received at any chosen distance along the core by a small crystal geophone resting on the specimen. The beginning of the supersonic pulse and the wave form of the received disturbance, together with the marks of an accurate timer by a quartz clock, are made visual and stationary on the screen of a cathode-ray oscillograph and the travel-time is measured. Thus the core is picked up at different distances and a travel-time curve is drawn from which the velocity of the waves is determined.The method is interpreted and the measuring device described. Graphs give several travel-time curves of different rock samples, drill cores, metal rods and rods of other solid materials. The elastic moduli E of the samples are communicated, and an example is given for determining Poisson's ratio S from longitudinal and transversal velocities on two cores of sandstone.

Notizen: Two geometric methods are given: one for estimating the position of mass distributions from the gravity anomalies, the other for determining the position of a thin plate of magnetized material from the magnetic anomalies. Finally a computational form of Nettleton's method for the determination of density is given.

Notizen: The supply of drinking water and water for general use in the towns and communities of Western Germany is in many cases insufficient. In order to eliminate the difficulties in the supply of water, geophysical methods have been applied to a large extent since the end of the war.The most important hydrological problems, which were solved successfully by geo-electrical measurements, are as follows:〈list xml:id="l1" style="custom"〉1Search for, and delimitation of, areas with salty ground water.2Investigation of the geological situation in catchment areas for large waterworks, and the finding of suitable places for the establishment of new plants, and in particular.3Search for and determination of the thickness and nature of water-bearing sands and gravels and of the relief of the underlying impervious strata.Some typical examples are presented herewith.

Notizen: The main features of the gravimetric map of the Gharb can be related to the shape of the basement, covered by cretaceous and miocene layers, with a total maximum thickness of 13,000 feet. For the interpretation of local features, in the northern part of the basin, first a regional anomaly has been drawn, then the map of the first derivative has been established.Both maps are compared with geological maps and seismic and electrical surveys. The results are the following:As for method, the advantages and limitations of both processes are outlined.As for geological interpretation, it is suggested that most of the local features of the gravimetric map are due to the preriffan tectonics.

Notizen: In the Cannock Chase Coalfield the rocks of the overburden are heavily waterlogged, thus constituting a source of difficulty and even danger to the miner. In order to ensure maximum safety with the maximum use of reserves, the area has been investigated by boreholes and by resistivity surveys.In this paper a short summary of the resistivity work is given, with especial reference to electrode arrangement and methods of interpretation used. Where applicable, comparison between resistivity evidence and borehole data is shown.

Notizen: This paper summarizes and extends the published information on the theoretical design of electromagnetic geophones. Both moving-coil and moving-armature instruments are considered, their behaviour compared and various design criteria established.

Notizen: After a short introduction, some examples of obliques multiple reflexions are treated and possible solutions given.

Notizen: Part I of this paper contains the presentation of a new analysis of observational material, mainly from Eskdalemuir, and describes some unexpected properties of geomagnetic fluctuations. The chief of these are (a) that there is a change of type at sunset from a continuous flux of disturbance to a comparative quiet punctuated by short damped wave trains, and (b) that the daytime fluctuations have a spectrum with definite fine structure. Part II is a discussion of the probable origin of geomagnetic pulsations. By comparing the characteristics found in Part I with those reported by previous observers it is concluded that the effects have a common cause, and very general arguments are then put forward to show that their origin is terrestrial. A survey of possible physical models points, after elimination, to a magneto-hydrodynamical resonance in one or more of the ionospheric layers.

Notizen: In an earlier paper it was suggested that it was failure in the region between 250 and 600 km below the surface which determined the periodicity of orogenic phenomena. In this paper estimates of the cross-sectional areas of the oceanic troughs and of the mass deficiencies reflected in the strips of large negative gravity anomalies are given and it is inferred that the interval between successive periods of failure is 50 million years.It is pointed out that if the troughs are formed in the manner described in the earlier paper then a regression of sea-level of about 70 metres will occur as a result of their formation. Finally some aspects of the development of the trough regions into mountain ranges are discussed qualitatively.

Notizen: The results are given of the harmonic analysis of the Admiralty magnetic charts of declination, horizontal intensity and inclination for the epoch 1942.5. Within the limits of observational error, the Earth's magnetic field appears to be entirely of internal origin. There is no evidence of a dipole field of external origin greater than 0-1 per cent of the field of internal origin. The intensity of the dipole field is at present decreasing at a rate of about 5 per cent per century. The geomagnetic poles have a westerly drift at a rate of 4°-5 per century; the north magnetic dip pole is moving in a direction a little to the west of north, but the south magnetic dip pole appears to be practically stationary. In consequence of the dearth of magnetic data over the oceans since 1929, magnetic charts are becoming less accurate and there is a great need for airborne magnetic surveys of ocean areas.

Notizen: This paper, which was almost completed* by Dr Corkan just before his death in 1952, gives a method of analysing observations of the tilting of the Earth's surface. The method combines observations from two places and assumes only that the body tilt due to the direct yielding to the attractive forces is simply related to the equilibrium form, but with a constant phase lag, and that the semidiurnal constituents in the load tilt have the same ratios as in the loading tide. It is shown that these ratios are very stable over large parts of the oceans, and a useful table is given for the main seas and oceans. This method avoids the uncertainties of computation of the loading tide which have caused many difficulties in previous investigations, and it automatically eliminates the greater part of the secondary effects of the more distant oceanic tides.

Notizen: The theory of the calculation of the detailed undulation of the geoid from gravity by Stokes's integral is usually given to first order, and there are some approximations which may be important in mountainous places. Some are trivial but the change of undulation with height is not. Discussion of this involves the definition of orthometric height and of the geoid. With suitable definitions the undulations of the geoid are the same as those of equipotential surfaces at external points, so that the latter may be calculated directly without additional correction for changes with height. The free-air correction to gravity is determined by these definitions and conditions; for geodetic purposes the fundamental quantity is not the change of gravity with height but the difference of geopotential. The correction derived in this paper thus differs slightly from those commonly in use and there are consequently some small errors in the figure of the Earth derived with the use of the letter.

Notizen: The gravimeter surveys made by the Anglo-American Oil Company (now the Esso Petroleum Company), the Anglo-Iranian Oil Company, the Geological Survey, and the Department of Geodesy and Geophysics of Cambridge University depend on about 600 base stations, of which those in any one survey are connected by a strong network of first order measurements of gravity differences. There are sufficient connections between base stations of different surveys for all the surveys to be compared and combined into one uniform system. The largest discrepancies between surveys arise from errors in the calibration factors of the gravmeters and the surveys have therefore been adjusted to six precise pendulum observations at stations between Aberdeen and Southampton.The adjustment has been carried out in three stages, The first is the preliminary adjustment of sets of observations made with the same instrument. The second is the calculation of gravity values at 120 principal stations selected from all 600 base stations, many of the 120 being common to two or more surveys; pendulum observations are included and the gravimeter calibration factors are determined. The gravity values are expressed as differences from the value at the Pendulum House, Cambridge Observatory. In the third stage, which it is hoped to report elsewhere, the remaining base station values are revised to agree with the 120 principal stations and the calculated calibration factors. It is shown that the discrepancies between this procedure and the simultaneous adjustment of all 600 base station values are not serious.The standard deviations of single observations as determined from the internal errors of surveys range from 0.05 mgal to 0.27 mgal. Comparisons between different surveys indicate larger errors and it is possible that stations are not re-occupied exactly by different observers. Observations are weighted according to the variability between surveys, and the residuals of measured differences of gravity are generally consistent with this.Of the 300 observations between the 120 principal stations, 3 have residuals greater than three times the standard deviation. The values calculated for the 120 stations have standard deviations mostly between 0.1 and 0.2 mgal. Secular changes of heights of stations may in time lead to greater uncertainty.The difference between the value of gravity at the Pendulum House, Cambridge Observatory, and that at the site of the absolute determination at the National Physical Laboratory, Teddington, is 72.17 mgal, s. d. 0 008 mgal, and the value of gravity at Cambridge on the Potsdam system is therefore 981 268-5 mgal, assuming the value at Teddington to be 981 196.3 mgal (Cook, 1952 a). It is, however, recommended that gravity values within the British Isles should continue to be based on the value of 981 265 mgal at Cambridge (Bullard and Jolly, 1936).

Notizen: A rise in sea-level at the rate of 1 cm per century following a reduction in the extent of ice in glaciated regions results in an increase of the moment of inertia of the Earth about its axis of rotation sufficient to lengthen the day by 10-4 second per century provided there is no isostatic compensation. The consequent apparent secular acceleration of the Moon is 2 seconds of arc per century per century. The changes however are negligible if immediate and complete isostatic compensation occurs. A tentative discussion of climatic and glaciological evidence indicates that fluctuations of sea-level do occur and that their effect on the Moon's apparent acceleration may be appreciable. This re-opens the question of the cause of the Moon's apparent acceleration which is usually attributed to the deceleration of the Earth by tidal friction. The change in tidal friction due to a rise in sea-level is very small and has not been sufficient to produce the observed change in the Moon's acceleration.

Notizen: The depth of the level of no strain and the stress distribution have been calculated using Jeffreys's temperature distribution. It is found that the depth of the level of no strain is 59 km, that the stress difference in the crust increases at the rate of 0.6 dyn/cm2 year and that the decrease in the radius in 200 million years is 0.6 km. A relation between the decrease in radius and the heat loss per unit area is derived and from this relation it is shown that the possible changes in the parameters will not bring the contraction into accord with geological estimates. It is pointed out that the stress differences increase much more rapidly in relation to the strength at depths of 250 to 600 km and that failure should begin in this region. On this basis the cross-sectional area of an ocean deep is found to be 1400 km2.The lower mantle and the core are compressed as a result of cooling between the surface and 700 km. This compression is relieved when deep-focus earthquakes occur. It is calculated that increases in the length of the day totalling about 31/2 sec will occur in a period of failure of the mantle. Using a formula of Lapwood it is shown that the heating effect associated with the compression of the core is of the order of 1017 erg/sec, and that during failure of the mantle the cooling effect is likely to be much greater. Finally it is shown that the present rate of dissipation of energy in earthquakes is very much greater than the rate of generation of strain energy as a result of cooling.

Notizen: When account is taken of the angular momentum of surface masses moving relative to the solid Earth it is found that the equations governing the variation of latitude are not sensibly affected by changes in the rate of rotation and that the equations previously used are adequate if correction terms are added to account for the angular momentum which may be large enough to have an observable effect.

Notizen: The measurement of well velocity data in the well of Scheibenhardt I has shown that it is possible to observe a well noticeable measurable increase of the travel time of seismic waves when approaching a disturbance. The tectonic event of the disturbance is combined in this case with a disorder (shattering) of the layers without subsequent cementation.The significance of these anomalies for reflection seismics is discussed. When existing they will then overlap the diffraction, treated by Th. Krey.

Notizen: The article is based on data from 74 seismic well velocity surveys in N.W. Germany.The effect of overburden is illustrated by means of diagrams representing interval velocities against depth. To eliminate observational errors and lithological variations from well to well, interval velocities from about the same depth are averaged. Thus, relatively uniform curves are obtained for lower Tertiary, Upper Cretaceous, and Lower Cretaceous (Albian), making the effect of overburden better evident than from individual observations. The vertical gradient of velocity for these geological sections are given. Furthermore, they are compared with curves for Lower Tertiary and Cretaceous obtained in N. America. Due to its high lime content, the Upper Cretaceous of N.W. Germany has a much higher velocity than that observed in the Cretaceous of N. America. The curves for shales of the Lower Tertiary and Lower Cretaceous (Albian), however, are similar in both countries. In older formations, on the other hand, e.g. Jurassic and Triassic, lithologic character has the dominant influence and the effect of overburden is rather small and often scarcely noticeable.The data considered cover a depth range down to 2,700 meters. The interval velocities are generally based on the use of various equal intervals.

Notizen: The gravity effect of earth tides was measured simultaneously at 26 stations, with 2 instruments at 3 of the stations. After a description of the stations, the corrections on the measurements are described. The results for the separate measurements are given and it can be stated that, within the accuracy of the measurements 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR82:GPR_82_mu1" location="equation/GPR_82_mu1.gif"/〉 is very probably constant and has a value of 1.22. If this value is combined with Nishimura's value 0.66 for (1 − h + k), it can be shown that Takeuchi's earth models fit these values provided a value of 2.7 is taken for the surface density of the earth. The importance of a constant value for 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR82:GPR_82_mu1" location="equation/GPR_82_mu1.gif"/〉 in gravity surveys is pointed out.

Notizen: A ruler has been constructed to solve seismic refraction problems with horizontal or slightly inclined layers.