Seismic velocity-ratio in the crust and uppermost mantle in southeast Wellington province,New Zealand

The regional variation of the seismic velocity-ratio () over a 200 km long traverse has been studied by means of microearthquake surveys. The Wadati-plot method is used with a minimum of four P and S arrivals for each of 49 earthquakes. The area as a whole is found to be characterized by a value of 1.74–1.76 for earthquakes of depth 12–40 km, except in a 50 km long section near Wellington, where is low at 1.60. This low has been attributed to the fault zones in the region. A small change of is observed between the upper crust (5 km) and lower crust (12 km), but there is no change of between the lower crust and uppermost mantle.     

Numerical study of non-linear storm-surges

Summary The problem of storm-surges is investigated in a rectangular basin, setting up a numerical hydrodynamical model using the shallow-water equations. The forcing exerted by the atmosphere is given in the idealized form of a constant wind blowing over a section of the basin. The case in which the window of wind is moving is considered and for a basin that has the same dimensions of the Adriatic Sea. The conditions that give the maximum surge at one edge of the basin are investigated.

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Riassunto Il problema relativo alle storm-surges viene studiato in un bacino rettangolare, costru endo un modello idrodinamico numerico ed usando le equazioni relative ad acqua poco profonda. Lo stress esercitato dall'atmosfera è dato nella forma idealizzata di un vento costante che soffia sopra una sezione del bacino. Si considera il caso in cui la finestra di vento è in moto e per un bacino che ha le medesime dimensioni del mare Adriatico. Si studiano le condizioni che provocano il massimo dell'innalzamento ad un estremo del bacino.

     

On the frequency modulation of VLF emissions

The VLF-wave frequency modulation efficiency as a function of magnetosphere plasma parameters under the weak pitch-angle diffusion regime is studied. The study is based on the VLF growth-rate modulation both in the magnetosphere equatorial plane and after integrating along the magnetic field line. It is shown that for the typical quiet magnetosphere plasma parameters the relative shift of the maximum intensity frequency _m/_m is approximately equal to relative disturbance of the magnetic field in the magnetosphere equatorial plane, but may exceed it when both electron temperature anisotropy and the parameter are small; here is the total-to-warm electron content ratio and is the electron parallel beta. It is also shown that relative shift of the maximum intensity frequency _m/_m after integrating along the field line is not less than 50% from its value at the equatorial plane, which allows the use of the equatorial-plasma-parameter data to estimate the VLF frequency modulation on the ground. The upper cut-off frequency modulation is considered as well. The calculated theoretical sonagrams show that this frequency modulation may be related to the non-dispersive and to the inverted-V structures of QP hiss.     

Observed Response of the Ionospheric F2–Layer and Lower Thermosphere to Geomagnetic Storms during High Solar Activity

The response of the critical frequency of the ionosphere F2–layer, described by its main Fourier components (daily constant, diurnal and semidiurnal waves) and the lower thermosphere dynamics to the geomagnetic storms in July 1991 and February 1992 is studied. The daily constant displays a negative response, however, the magnitude of reaction depends on the season and latitude. The amplitudes of diurnal and semidiurnal waves increase during a geomagnetic storm, as this enhancement is very strong at high latitudes in winter. The prevailing neutral wind, especially the zonal wind, shows an inclination to decrease during the geomagnetic storm (the effect is more distinct in summer). The amplitudes of diurnal and semidiurnal tides also demonstrate a tendency toward reduction during high geomagnetic activity.     

On the propagation of finite Love Waves

Summary The problem of the propagation of finite Love Waves in a heterogeneous elastic half space lying over a homogeneous elastic half space, using the quasilinear stress-strain relation due toS. Ferhst [4] is considered in detail. The variations of the parameter in the layer assumed to be of the form 1= 0e ^z, 0e ^z where is a constant andz is distance measured from the surface into the layer.     

A note on the general concept of wave breaking for Rossby and gravity waves

A recently proposed general definition of wave breaking is further discussed, in order to deal with some points on which misunderstanding appears to have arisen. As with surface and internal gravity waves, the classification of Rossby waves into breaking and not breaking is a generic classification based on dynamical considerations, and not a statement about any unique signature or automatically recognizable shape. Nor is it a statement about passive tracers uncorrelated with potential vorticity on isentropic surfaces. A strong motivation for the definition is that proofs of the nonacceleration theorem of wave, mean-flow interaction theory rely, explicitly or implicitly, on a hypothesis that the waves do not break in the sense envisaged.The general definition refers to the qualitative behaviour of a certain set of material contours, namely those, and only those, which would undulate reversibly, with small slopes, under the influence of the waves' restoring mechanism, in those circumstances for which linearized, nondissipative wave theory is a self-consistent approximation to nonlinear reality. The waves' restoring mechanism depends upon the basic-state vertical potential density gradient in the case of gravity waves, and upon the basic-state isentropic gradient of potential vorticity in the case of Rossby waves. In the usual linearized theory of planetary scale Rossby waves on a zonal shear flow, the relevant material contours lie along latitude circles when undisturbed.     

Solution of stochastic groundwater flow by infinite series,and convergence of the one-dimensional expansion

This paper investigates analytical solutions of stochastic Darcy flow in randomly heterogeneous porous media. We focus on infinite series solutions of the steady-state equations in the case of continuous porous media whose saturated log-conductivity (lnK) is a gaussian random field. The standard deviation of lnK is denoted . The solution method is based on a Taylor series expansion in terms of parameter , around the value =0, of the hydraulic head (H) and gradient (J). The head solution H is expressed, for any spatial dimension, as an infinite hierarchy of Green's function integrals, and the hydraulic gradient J is given by a linear first-order recursion involving a stochastic integral operator. The convergence of the -expansion solution is not guaranteed a priori. In one dimension, however, we prove convergence by solving explicitly the hierarchical sequence of equations to all orders. An infinite-order stochastic solution is obtained in the form of a -power series that converges for any finite value of . It is pointed out that other expansion methods based on K rather than lnK yield divergent series. The infinite-order solution depends on the integration method and the boundary conditions imposed on individual order equations. The most flexible and general method is that based on Laplacian Green's functions and boundary integrals. Imposing zero head conditions for all orders greater than one yields meaningful far-field gradient conditions. The whole approach can serve as a basis for treatment of higher-dimensional problems.     

Rayleigh waves in an inhomogeneous medium

Summary Dispersion in Rayleigh waves is discussed for semi-infinite media with = ₁(1 ± cos s z) and = ₁(1 ± cosh s z), being the rigidity of the medium. A few workers tried with the above Fourier type of model but failed to find the dispersive nature. Because they neglected s due to the complexity of the calculation they arrived at a non dispersive frequency equation. This difficulty is removed in this paper and a dispersive frequency equation is obtained which shows both direct and inverse dispersion. The second model leads to non-convergent solution forz but shows many interesting results which are also discussed.     

Über die erdmagnetischen Anomalien in den Gebieten um die Ostsee

Zusammenfassung Das Gebiet um die Ostsee ist als erdmagnetisch stark gestört bekannt. Die Karte zeigt die Verteilung der intensiven Anomalien, wo Z 2000 and 5000 überschreitet. Der Gruppierung dieser Anomalien kann man eine ung.N Richtung zuschreiben.

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Summary The area around the Baltic Sea is known as magnetically intensely disturbed. The map shows the distribution of most intensive anomalies, where Z is more than 2000 and 5000 . The direction of the group of these intensive anomalies can be as appr.N supposed.

     

On the propagation of wave from a cylindrical cavity

Summary This paper discusses the disturbance produced in an infinite layer of non-homogeneous elastic material characterised by =0 ⁿ and =0ⁿ(n>0) where and are the density and shear modulus respectively of the material, due to periodic torsional force applied on the wall of a cylindrical hole in the layer. The variation of the displacement component with the radius vector is shown graphically and compared with the corresponding homogeneous case.     

Molecular refraction in the Earth's mantle

The Drude law (molecular refraction) for the temperature radiation in a monoatomic model of the Earth's mantle is derived. The considerations are based on the Lorentz electron theory of solids. The characteristic frequency (or eigenfrequency) of independent electron oscillators (in energy units, ) is identified with the band gapE _G of a solid. The only assumption is that solid material related to the Earth's mantle has the mean atomic weight A21 g/mole, and its energy gap (E _G) is about 9 eV. In this case the value of molecular refraction (in cm³/g) is (n ²–1)/=0.5160.52, where andn are the density and the refractive index at wavelength _D=0.5893 m (sodium light), respectively. The average molecular refraction of important silicate and oxide minerals with A21, obtained byAnderson andSchreiber (1965) from laboratory data, is , where denotes the mean arithmetic value calculated from three principal refractive indices of crystal. For the rock-forming minerals with 19A<24 g/mole the new relation was found byAnderson (1975).     

Multifractal measures,especially for the geophysicist

This text is addressed to both the beginner and the seasoned professional, geology being used as the main but not the sole illustration. The goal is to present an alternative approach to multifractals, extending and streamlining the original approach inMandelbrot (1974). The generalization from fractalsets to multifractalmeasures involves the passage from geometric objects that are characterized primarily by one number, namely a fractal dimension, to geometric objects that are characterized primarily by a function. The best is to choose the function (), which is a limit probability distribution that has been plotted suitably, on double logarithmic scales. The quantity is called Hölder exponent. In terms of the alternative functionf() used in the approach of Frisch-Parisi and of Halseyet al., one has ()=f()–E for measures supported by the Euclidean space of dimensionE. Whenf()0,f() is a fractal dimension. However, one may havef()<0, in which case is called latent. One may even have <0, in which case is called virtual. These anomalies' implications are explored, and experiments are suggested. Of central concern in this paper is the study of low-dimensional cuts through high-dimensional multifractals. This introduces a quantityD _q, which is shown forq>1 to be a critical dimension for the cuts. An enhanced multifractal diagram is drawn, includingf(), a function called (q) andD _q.This text incorporatesand supersedes Mandelbrot (1988). A more detailed treatment, in preparation, will incorporateMandelbrot (1989).     

On the determination of the European gravimetric geoid

Summary The method of the automated computation of the gravimetric deflections of the vertical and of the geoidal heights for the European region is described. The work was carried out during the period 1986–1988 by the Topographic Service of the Czechoslovak Army. The computation applies to 20 sheets of the international map 1:1 000 000 (total area of =16^c, =30^c - see Fig. 1). The mean values of the free-air anomalies for each surface element =5, =7.5, approximately 9 × 9 km, were used with radius of integration of 300 km.     

The magnetic observatory of Pendeli (Athens,Greece)

Summary A new magnetic observatory, named the Magnetic Observatory of Pendeli, was established and put in operation in 1958 near Athens (Greece). This Observatory was organized by and belongs to the Greek «Institute for Geology and Subsurface Research». The geographical position of the Pendeli Observatory is given by =38° 02.8, =23°51.8 andh=495 m (above sea level). The gemagnetic coordinates of the same are =36°.2, =102°.0. The Observatory is situated near Pendeli Mt. (18 km NEE of Athens). The site of the Observatory consists of marmor underlain by mica schists, both magnetically inactive.The building of the Observatory is constructed of stone and its roof made of tiles. The magnetograph room is in the underground of the building. The magnetic and thermal conditions in the variometer room are satisfactory enough.The variometers of the Observatory forH andZ are of the magnetic balance type. ForD a fibre suspension declinometer is used. The scale values of the variometers are _H =7.2 /mm, _D =1.0/mm (7.6 /mm), _Z =11.5 /mm. The speed of recording amounts to 12 mm/h and the width of the record is 9 cm.The Pendeli Observatory has been operating since April 1958. The record is changed every day. The scale and base-line values are determined every 10 days. The room for the absolute measurements is found in the ground floor of the building. A field magnetic theodolite is being used in the absolute measurements.D is measured with two magnets in a fibre suspension declinometer.H is measured by means of the deflection oscillation method and with a QHM as well. For the measurement ofI an earthinductor is available. The values of the magnetic elements are properly corrected in order to represent the external normal field.     

Physical and coupled fully three-dimensional numerical modeling of pressurized bottom outlet flushing processes in reservoirs

Sediment deposition in reservoirs is an important research topic in engineering practice. Reservoir sedimentation has the potential to affect ood levels, drainage for agricultural land, pump station and hydropower operation as well as navigation. This paper describes the development of a coupled fully three-dimensional (3D) numerical model for the prediction of the local sediment ushing scour upstream of the bottom outlet. The presented numerical model solves the Navier-Stokes equations in conjunction with the k- turbulence model which includes both sediment transport and hydrodynamic parameters. The proposed coupled fully 3D numerical model is used to simulate experimental tests based on non-cohesive sediment. The geometric features of the scour hole (temporal and spatial hole devel- opment) upstream of the bottom outlet were reasonably well predicted compared to the experimental data. Furthermore, the velocity eld upstream of the bottom outlet was in good agreement with mea- surements. The proposed numerical model for bottom outlet ushing was, therefore, validated because of its ability to accurately predict the scour hole development during the ushing process. The proposed numerical model can be considered reliable provided that the model is correctly calibrated and set up to re ect the conditions of a particular case study.     

Source characteristics of the 1992 Nicaragua tsunami earthquake inferred from teleseismic body waves

We analyzed the broadband body waves of the 1992 Nicaragua earthquake to determine the nature of rupture. The rupture propagation was represented by the distribution of point sources with moment-rate functions at 9 grid points with uniform spacing of 20 km along the fault strike. The moment-rate functions were then parameterized, and the parameters were determined with the least squares method with some constraints. The centroid times of the individual moment-rate functions indicate slow and smooth rupture propagation at a velocity of 1.5 km/s toward NW and 1.0 km/s toward SE. Including a small initial break which precedes the main rupture by about 10 s, we obtained a total source duration of 110 s. The total seismic moment isM _o =3.4×10²⁰ Nm, which is consistent with the value determined from long-period surface waves,M _o =3.7×10²⁰ Nm. The average rise time of dislocation is determined to be 10 s. The major moment release occurred along a fault length of 160 km. With the assumption of a fault widthW=50 km, we obtained the dislocationD=1.3 m. From andD the dislocation velocity isD=D/0.1 m/s, significantly smaller than the typical value for ordinary earthquakes. The stress drop =1.1 MPa is also less than the typical value for subduction zone earthquakes by a factor of 2–3. On the other hand, the apparent stress defined by 2E _s /M _o , where andE _s are respectively the rigidity and the seismic wave energy, is 0.037 MPa, more than an order of magnitude smaller than . The Nicaragua tsunami earthquake is characterized by the following three properties: 1) slow rupture propagation; 2) smooth rupture; 3) slow dislocation motion.