On the characteristics of vlf emissions in the upper ionosphere and on the ground

auuau uu muna a f>1,5 , aumua ¶rt; a nmua uu m u a ¶rt; a mau. mu a aum nm uu, umu a mauu aa (L=2,1) n¶rt; nm uu (L=5). m mmmum mu umua uu, umu a mu mau. au uu a nm m, m a um nmam a 2000–3000 u anu u a L=2,2–5,9. au mmmu nma aamumu a u nmu uu a¶rt;am u amu aua uu a L 3,5. aa, m a mauu aa u ¶rt;a a¶rt; nuu uu a , umum uuu n¶rt; a¶rt;a a nmu. au a n¶rt;num, m am a L 3,5,¶rt; aam au uu u au mmu nma aamumu a u nmu uu, aa ¶rt;amua anau a nana. m u m amu mm au anum u ¶rt; ¶rt;a ua n¶rt;u anmau u ¶rt; — ua.     

Q measurements for PhaseX overtones

Linear stacking procedures are used to retrieve the attenuation of 91 modes belonging to the 3rd, 4th and 5th Rayleigh overtones branches in the 80–160 s period range, and contributing to the so-called PhaseX wave group. Our data show in general slightly less attenuation than expected from available models. Data space inversion shows that, when combined with previously measured fundamental modeQ's, this new dataset improves resolution significantly in the 1000–2000 km depth range. Based on this remark, we carry out a number of parameter space inversions. Our results suggest a narrow (80–200 km) zone of high attenuation (Q =75–90), low attenuation in the intermediate mantle (670–1500 km); (Q 350), and lower values in the deeper mantle (Q 200).     

Deep electrical structure under central Europe

Summary The model of the electrical conductivity distribution within the Bohemian Massif to mid-upper mantle depths was derived from magnetotelluric and magnetic continuum long-period data of the Budkov Observatory (Geophysical Institute, Acad. Sci. Czech Republic., Prague) and from the ISL (Induction Scale Lengths) data of the Prhonice Observatory. The ranges of apparent resistivities in the Bohemian Massif (BM) are compared with those obtained at relevant central European observatories. The conductivity profile is estimated from the resistivity/depth graph corresponding to substitute perfect conductor inversion.Dedicated to the Memory of Professor Karel P     

Structure of the crust in the Black Sea and adjoining regions from surface wave data

Group velocities of Rayleigh and Love waves along the paths across the Black Sea and partly Asia Minor and the Balkan Peninsula are used to estimate lateral variations of the crustal structure in the region. As a first step, lateral variations of group velocities for periods in the range 10–20 s are determined using a 2D tomography method. Since the paths are oriented predominantly in NE–SW or N–S direction, the resolution is estimated as a function of azimuth. The local dispersion curves are actually averaged over the extended areas stretched in the predominant direction of the paths. The size of the averaging area in the direction of the best resolution is approximately 200 km. As a second step, the local averaged dispersion curves are inverted to vertical sections of S-wave velocities. Since the dispersion curves in the 10–20 s period range are mostly affected by the upper crustal structure, the velocities are estimated to a depth of approximately 25 km. Velocity sections along 43° N latitude are determined separately from Rayleigh and Love wave data. It is shown that the crust under the sea contains a low-velocity sedimentary layer of 2–3 km thickness, localized in the eastern and western deeps, as found earlier from DSS data. Beneath the sedimentary layer, two layers are present with velocity values lying between those of granite and consolidated sediments. Velocities in these layers are slightly lower in the deeps, and the boundaries of the layers are lowered. S-wave velocities obtained from Love wave data are found to be larger than those from Rayleigh wave data, the difference being most pronounced in the basaltic layer. If this difference is attributed to anisotropy, the anisotropy coefficient = (SH - SV)/Smean is reasonable (2–3%) in the upper layers, and exceeds 9% in the basaltic layer.     

Station Correction of the seismic station Kašperské Hory for short-periodP waves

Summary The magnitude station correction of the seismic station Kaperské Hory, related to Prhonice, was determined for the vertical component of short-period P waves.     

Local geology and dynamic parameters of seismic waves

Summary Amplitudes and periods of seismic waves recorded both in the short-period and in the intermediate-period ranges at the seismic stations Prhonice, Praha and Kaperské Hory are influenced by the tectonic situation in the focal regions rather than by the anisotropic structures of the geologic formations underlying the stations. Large amplitude variations and differences in periods due to instrumental effects were also found.     

A comment on the effect of discretization on dispersion

a mamumuu m, m n¶rt; u a¶rt;a au, um ¶rt;umuau. aam, m a au ¶rt;unu a¶rt;a au n ¶rt;umuauu u n¶rt; nu a an¶rt; a u uu aa ,¶rt; h a ¶rt;umuauu.     

Anelasticity of the crust and upper mantle beneath north and central India from the inversion of observed Love and Rayleigh wave attenuation data

The fundamental mode Love and Rayleigh waves generated by earthquakes occurring in Kashmir, Nepal Himalaya, northeast India and Burma and recorded at Hyderabad, New Delhi and Kodaikanal seismic stations are analysed. Love and Rayleigh wave attenuation coefficients are obtained at time periods of 15–100 seconds, using the spectral amplitude of these waves for 23 different paths along northern (across Burma to New Delhi) and central (across Kashmir, Nepal Himalaya and northeast India to Hyderabad and Kodaikanal) India. Love wave attenuation coefficients are found to vary from 0.0003 to 0.0022 km^–1 for northern India and 0.00003 km^–1 to 0.00016 km^–1 for central India. Similarly, Rayleigh wave attenuation coefficients vary from 0.0002 km^–1 to 0.0016 km^–1 for northern India and 0.00001 km^–1 to 0.0009 km^–1 for central India. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtainQ ^–1 models for the crust and uppermost mantle beneath northern and central India. Inversion of Love and Rayleigh wave attenuation data shows a highly attenuating zone centred at a depth of 20–80 km with lowQ for northern India. Similarly, inversion of Love and Rayleigh wave attenuation data shows a high attenuation zone below a depth of 100 km. The inferred lowQ value at mid-crustal depth (high attenuating zone) in the model for northern India can be by underthrusting of the Indian plate beneath the Eurasian plate which has caused a low velocity zone at this shallow depth. The gradual increase ofQ ^–1 from shallow to deeper depth shows that the lithosphere-asthenosphere boundary is not sharply defined beneath central India, but rather it represents a gradual transformation, which starts beneath the uppermost mantle. The lithospheric thickness is 100 km beneath central India and below that the asthenosphere shows higher attenuation, a factor of about two greater than that in the lithosphere. The very lowQ can be explained by changes in the chemical constitution taking place in the uppermost mantle.     

On the problem of constructing density models of the lithosphere

mm ¶rt;u um a z num a / mua a (¶rt; ¶rt;u) a a n umnmauu yaumau u uu ¶rt;a. mam unau a um aau u mmu, ma¶rt;amy an¶rt;u nmmu u m¶rt; umnmauu am u m¶rt; auam ¶rt;o ¶rt;o. ¶rt;am namua ma¶rt;amo n¶rt;¶rt;a nmu u m nmm ¶rt;.     

On the cessation of seismicity at the base of the transition zone

Through a detailed analysis of seismicity at the base of the transition zone, we obtain an updated value of the maximum reliable depth of confirmed seismicity, we investigate regional variation in the maximum depth of seismicity among those Wadati-Benioff zones which reach the bottom of the transition zone, and we attempt to quantify the maximum possible rate of seismic release in the lower mantle compatible with the failure to detect even a single event since the advent of modern seismological networks. We classify deep subduction zones into three groups: those whose seismicity does not reach beyond 620 km, those whose seismicity appears to terminate around 650–660 km, and Tonga-Kermadec (and the Vityaz cluster) whose seismicity extends to 685–690 km. We suggest that the depth extent of seismicity is controlled by the depth of the pv + mw transition responsible for the 660-km seismic discontinuity, which is deflected to greater depths in cold slabs than in warmer ones. We note that this transition marks the depth below which thermal perturbation of phase transitions no longer generates buoyancy anomalies and their large attendant down-dip compressive stresses and below which strain energy generated by other mechanisms may not accumulate to seismogenic levels due to superplastic weakness in fine-grained materials. We find that the maximum level of seismic activity in the lower mantle must be at least three orders of magnitude less than that observed in the transition zone.     

Deep seismically active fracture zones in Ecuador and northern Peru

Summary A system of 15 seismically active fracture zones was delineated on the basis of the distribution of earthquake foci in the continental lithosphere of northern Peru. The position and width of the outcrop, thickness, dip and maximum depth of the individual fracture zones were estimated and correlated with surface geological and tectonic phenomena. The pattern of the seismically active fracture zones in the equatorial part of Andean South America and the existing fault plane solutions indicate an east-west compression of the continental wedge induced by the subduction of the Nazca plate.

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uma 15 uu amu a a aa a auu an¶rt;u a mu muma um . u n¶rt; nu u uua a nmu, mua, u auaaua m¶rt; a u n¶rt; u nmau nmu u mmu amu. aam an¶rt;u mu a amua amu a¶rt; uu u mu ¶rt;a n aua mu naam a m-ana¶rt; amu muma ua ¶rt;mu ¶rt;uu num aa n¶rt; auau mum.

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Visiting professors at Instituto Geofísico and Facultad de Geología, Minas y Petróleos, Escuela Politécnica Nacional, Quito (Ecuador).     

The elastic constants of crystalline limestone computed from the velocities of body waves

m¶rt; uu nu nm u m n¶rt; , nua [4], una ¶rt; aa uma u um aumnuu. ma amuaa amu ¶rt; nm nu nm, m annuum uamuu u ¶rt;uauu ma n¶rt; . m u mu nm um ¶rt;a, nau au. ma ¶rt;a¶rt;amu nm u m n¶rt; n¶rt;um m m au.     

Resonance frequencies in the sun's motion

Summary The position of the Sun with respect to the gravity centre of the Solar System for the beginning of every year of a 3100 — year time series was determined and the harmonic analysis of the parameters of the Sun's motion about the gravity centre was carried out.

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unu u u ¶rt; ¶rt;¶rt; u ¶rt; ¶rt;u 3100 u c¶rt;uu u n ¶rt;uu u.

     

Bicubic spline smoothing of the data given at points of a rectangular network

Summary A computational method for fitting smoothed natural or periodic bicubic splines to data given at the grid points of a rectangular network is proposed. The one-dimensional smoothed spline fit, introduced by Reinsch, defines the smoothness properties well. These are generalized for a two-dimensional approximation by solving the corresponding variational problem. The defining equations are presented here together with an efficient method of determining the necessary parameters and computing the resultant spline.

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¶rt;u u m¶rt; annuauu ¶rt; uu auauu nau m m¶rt; a [12]. am am nua m¶rt; au m¶rt; a ¶rt; u ¶rt; n. nua aum n¶rt;aa ¶rt; annuauu ¶rt; uu, a¶rt;a uu auu a nu n mu, mmu uuuu naau uu ( m auam) uuuu naau, nu¶rt;uuu ¶rt; anauu. mam um uma uum, n m aum annuu u . namuu uu a omaa naa a FORTRAN.

     

Seismotectonic model of the upper part of the Earth's crust of Czechoslovakia

Summary A correlation of the earthquake occurrence on the territory of Czechoslovakia and in its close neighbourhood with the data on the neotectonic and geomorphological development of the respective area, the recent movements of the Earth's crust, the courses of photolineations and on the geophysical fields enabled the fundamental structural blocks in the upper part of the Earth's crust to be singled out. The contact zones established between the above blocks exhibit increased long-term movement tendencies particularly in the Neoid period. A seismotectonic model of the upper part of the Earth's crust of Czechoslovakia, compiled with the use of the data mentioned above, is described.

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u m uu mu a mumuu auu u mmu ¶rt;au n mmu,uu, ¶rt;uu , u nmu u uuuu n nua ¶rt;um mm u amu . a a ¶rt; muu au a¶rt;am amau ¶rt; ¶rt;uu, u¶rt; nu¶rt;. m n¶rt;aaa mmua ¶rt; amu aa a au¶rt;uauu n, nu¶rt;u a ua mumuu, u a u u n¶rt;uu au.

     

Ephemeris time,lunar orbital elements and FK4 equinox correction from the observations of the moon by the method of equal altitudes

ma n n¶rt;u u¶rt; u, m um u umuu ¶rt; amaa n nu , a¶rt;a n n a m. am nua ¶rt;a aau a¶rt;u n uumaa u ummna a ¶rt;u amuu 1965–1970 . mama u¶rt;, m na an amua ¶rt;mam ¶rt; m, m um n¶rt;um ¶rt;mam mm.     

On the propagation of wave from a cylindrical cavity,II

Summary We have discussed in the paper the disturbance produced in an infinite layer of nonhomogeneous elastic material characterised by = ₀ Z and = ₀ Z 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 depth of the layer is shown graphically and compared with the corresponding homogeneous case.     

Efficient estimates of points in a net constructed in stages

auau¶rt;u mu uam nua u mau a¶rt; ¶rt;a a au. a¶rt;a n¶rt;amm mau u mau, m mumu mu, a¶rt;a u aua n mana, nuam a man uu ¶rt;unuu aua ¶rt;uam (ma mum). u m umam mamumuu ma u a nma u u n¶rt;¶rt;u man. am ma au n¶rt; na ma¶rt;am n auau.     

The pulsation activity of a geomagnetic storm

um mam aau ¶rt; a¶rt;uaum nau mu m¶rt; a aum u a ¶rt;u uma.     

Application of A. C. demagnetization to investigate the stability of rock magnetization caused by lightning currents

Summary An apparatus is described which enables progressive demagnetization of rock specimens under alternating fields in order to remove the unstable components of magnetization while retaining a measurable fraction of the stable component.The apparatus is utilized to study the stability of magnetization created in rock specimens by artificial lightning currents. It is shown that the remanent magnetization due to strong lightning currents could be fairly stable and in certain cases peak a. c. fields of intensity as high as 1700 Oe may fail to destroy completely the effect of this hard component.Possible means for avoiding the magnetic noise effect of lightning on paleomagnetic investigations are discussed.

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Zusammenfassung Es wird eine Apparatur beschrieben die es ermöglicht, Gesteinsproben mit Hilfe von Wechselfeldern schrittweise zu Entmagnetisieren. Dabei werden die unstabilen Komponenten der Magnetisierung entfernt, während ein Teil der stabilen Magnetisierung erhalten bleibt.Die Apparatur wurde verwendet, um die Stabilität der in den Gesteinsproben durch künstliche Beblitzung erzeugten Magnetisierung zu untersuchen. Es wird gezeigt, dass die durch starke Blitze erzeugte remanente Magnetisierung recht stabil sein kann und dass es in gewissen Fällen selbst Wechselfeldern mit Feldstärken bis zu 1700 Oe nicht gelingt, diese harte Magnetisierung zum Verschwinden zu bringen.Möglichkeiten, um den störenden Einfluss der Blitze bei päleomagnetischen Untersuchungen zu vermeiden, werden besprochen.

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Part II of the dissertation Theoretical study of the magnetic attraction due to rock bodies and experimental investigation of the stability of rock magnetism submitted to the Swiss Federal Institute of Technology (ETH), Zurch, for the degree of Doctor of Natural Sciences.