Comparison of techniques that use the single scattering model to compute the quality factorQ from coda waves

Using simulated coda waves, the resolution of the single-scattering model to extract codaQ (Q _c ) and its power law frequency dependence was tested. The back-scattering model ofAki andChouet (1975) and the single isotropic-scattering model ofSato (1977) were examined. The results indicate that: (1) The inputQ _c models are reasonably well approximated by the two methods; (2) almost equalQ _c values are recovered when the techniques sample the same coda windows; (3) lowQ _c models are well estimated in the frequency domain from the early and late part of the coda; and (4) models with highQ _c values are more accurately extracted from late code measurements.     

Thermal regime of the Earth's outer core

Summary First an introduction into the dynamo problem and the core paradox is given. A novel theory of the volume dependence of Grüneisen's parameter is used for calculating the adiabatic temperatures on the assumption that the melting temperature of the material is reached at the boundary between the inner and outer cores of the Earth (IOB). On this condition, thermal convectionthroughout the outer core is impossible according to the melting-point curves ofKennedy andHiggins (1973) andLiu (1975), whereas it is permitted by that ofLeppaluoto (1972),Boschi (1975), andStacey (1977). Various possibilities of solving the core paradox are described.Mitt. d. ZIPE Nr. 682.     

Focal mechanism study of South American earthquakes

Summary This study presents the focal mechanism solutions of four South American earth-quakes. These solutions have been determined using the sign of the initial motion ofP wave, and the polarization angle ofS wave. A regional study of the strike of the fault plane, the direction of motion, and the regional stress pattern has been made in which the focal mechanism solutions determined byStauder andBollinger were also used.     

Application of the extreme value approaches to the apparent magnitude distribution of the earthquakes

The apparent magnitude of an earthquakey is defined as the observed magnitude value and differs from the true magnitudem because of the experimental noisen. Iff(m) is the density distribution of the magnitudem, and ifg(n) is the density distribution of the errorn, then the density distribution ofy is simply computed by convolvingf andg, i.e.h(y)=f*g.If the distinction betweeny andm is not realized, any statistical analysis based on the frequency-magnitude relation of the earthquake is bound to produce questionable results. In this paper we investigate the impact of the apparent magnitude idea on the statistical methods that study the earthquake distribution by taking into account only the largest (or extremal) earthquakes. We use two approaches: the Gumbel method based on Gumbel theory (Gumbel, 1958), and the Poisson method introduced byEpstein andLomnitz (1966). Both methods are concerned with the asymptotic properties of the magnitude distributions. Therefore, we study and compare the asymptotic behaviour of the distributionsh(y) andf(m) under suitable hypotheses on the nature of the experimental noise. We investigate in detail two dinstinct cases: first, the two-side limited symmetrical noise, i.e. the noise that is bound to assume values inside a limited region, and second, the normal noise, i.e. the noise that is distributed according to a normal symmetric distribution.We further show that disregarding the noise generally leads to biased results and that, in the framework of the apparent magnitude, the Poisson approach preserves its usefulness, while the Gumbel method gives rise to a curious paradox.     

Intraplate seismicity of the Pacific Basin, 1913–1988

We establish here a comprehensive database of intraplate seismicity in the Pacific Basin. Relocation and analysis of 894 earthquakes yield 403 reliable intraplate earthquakes during 1913–1988. These numbers do not include earthquake swarms, which account for another 838 events. Most of the remainder (304 events) are actually plate boundary earthquakes that have been erroneously located in intraplate regions. A significant number occur in recent years when location capabilities should have guarded against this situation. Relocations involve a careful linear inversion ofP andS arrivals, accompanied by a Monte Carlo statistical analysis. We have also attentively removed the high number of clerical errors and nuclear tests that exist in epicenter bulletins.A geographical examination of the relocated epicenters reveals several striking features. There are three NW-SE lineaments north of the Fiji Plateau and in Micronesia; diffuse seismicity and incompatible focal mechanisms argue against the southernmost, discussed byOkal et al. (1986) andKroenke andWalker (1986), as the simple relocation of the Solomon trench to the North. Besides another striking lineament, along the 130°W meridian, there is also a strong correlation between seismicity and bathymetry in certain parts of the Basin. In the Eastcentral Pacific and Nazca plates there are many epicenters on fracture zones and fossil spreading ridges, and hot spot traces like the Louisville, Nazca and Cocos Ridges also display seismicity.     

Far-field displacements from a rectangular fault with two rupture velocities

Summary Analytic expressions for the far-field displacement both in the time and the frequency domains are obtained for the kinematic earthquake model of a rupture which nucleates at a point, grows in the form of a rectangle and stops at a later time.The spectra ofS andP waves are analyzed with the object of determining fault dimensions from the corner frequencies. The approach by which the solution of the present problem is obtained can be extended to get closed form solutions to the problem of rupture front expanding in the form of a polygon and terminating over a fault area which has the form of another polygon.     

Attenuation of high-frequency earthquake waves in South America

Earlier attenuation studies for the South American continent indicate that for Sn and Lg waves there is low attenuation in the shield region east of the Andes, whereas in the west of South America, with some exceptions, there is high attenuation. Those studies, however, were nonquantitative. In this study theQ ₀ (1-Hz values) for Lg waves for South America are presented, based on a scattering model ofAki (1969) as extended byHerrmann (1980) for the coda waves of shallow local and near-regional earthquakes. The results of the codaQ method are compared with those obtained byNuttli's method (1973). TheseQ ₀ values are in good agreement with the apparentQ ₀ of Lg waves obtained by the latter method. The data were obtained from over 100 local and regional earthquakes recorded by 12 WWSSN stations throughout continental South America. They provided a range of frequencies from 0.4 to 1.4 Hz, for which the frequency dependence ofQ was investigated by assumingQ=Q ₀(f/f ₀). The observed data indicate that the tectonic region of western South America is characterized by lowQ ₀ and a large frequency-dependent factor , the values ranging from 150 to 350 and 0.4 to 0.7, respectively. TheQ ₀ values increase in the shield region east of the Andes, but frequency dependence decreases. The average crustalQ ₀ for north and central Argentina ranges from 420 to 580, and ranges from 0.2 to 0.3. TheQ ₀ is larger in the Brazil region, ranging from 580 to 980, and varies from 0.0 to 0.2. In the lower-attenuation region of eastern South America higher values of attenuation correlate with greater thickness of the sedimentary layers.     

CodaQ as a combination of scattering and intrinsic attenuation: Numerical simulations with the boundary integral method

Numerical modelling ofSH wave seismograms in media whose material properties are prescribed by a random distribution of many perfectly elastic cavities and by intrinsic absorption of seismic energy (anelasticity) demonstrates that the main characteristics of the coda waves, namely amplitude decay and duration, are well described by singly scattered waves in anelastic media rather than by multiply scattered waves in either elastic or anelastic media. We use the Boundary Integral scheme developed byBenites et al. (1992) to compute the complete wave field and measure the values of the direct waveQ and coda wavesQ in a wide range of frequencies, determining the spatial decay of the direct wave log-amplitude relation and the temporal decay of the coda envelope, respectively. The effects of both intrinsic absorption and pure scattering on the overall attenuation can be quantified separately by computing theQ values for corresponding models with (anelastic) and without (elastic) absorption. For the models considered in this study, the values of codaQ ^–1 in anelastic media are in good agreement with the sum of the corresponding scatteringQ ^–1 and intrinsicQ ^–1 values, as established by the single-scattering model ofAki andChouet (1975). Also, for the same random model with intrinsic absorption it appears that the singly scattered waves propagate without significant loss of energy as compared with the multiply scattered waves, which are strongly affected by absorption, suggesting its dominant role in the attenuation of coda waves.     

Magnetohydrodynamic oscillations due to precessional motion

Summary The motion of a non-viscous liquid medium with an ideal electrical conductivity, enclosed in the ellipsoidal cavity of an envelope subject to precessional motion, is investigated. Inside the cavity there is a toroidal magnetic field. It is proved that the precessional motion of the envelope generates forced oscillations of the medium with a period of 24 hours and two different types of eigen oscillations. Expressions for computing the amplitudes and frequencies of all types of oscillations are derived. The maximum values of disturbance fields are determined for geophysically acceptable parameters.     

P in the shadow zone of the earth's core—Part I

Summary Regional variations have been indicated in the slope of theP travel-time curve in the shadow zone of the earth's core. Further study is needed since the uncertainties of the slope are large, especially for the observations from North American stations. There is no significant difference between themean slope of theP travel-time curve in the 95°102.9 range and those obtained byJeffreys, andJeffreys andBullen. However, there is a significant difference between themean slope in the 103° to 135° range as obtained in this study, and those obtained byJeffreys andBullen, and in a later revision byJeffreys. Themean travel-time curve ofP in the shadow zone of the earth's core should be lowered. A trial travel-time table is given with amean slope of 4.41 sec/deg. This table is in close agreement with the times obtained byGutenberg andRichter, and with the trial travel-times ofLehmann. Under the assumption of diffraction the longitudinal wave velocity has been determined to be 13.7 km/sec at the core-mantle boundary.This paper was presented at the Annual Meeting of the Seismological Society of America Reno, Nevada, 1966.     

Zur Bestimmung einer rotenOscillatoria— ein Beitrag zur Variabilität vonOscillatoria rubescens D.C.

Summary For the purpose of determination a redOscillatoria species was after isolation cultivated and compared withO. rubescens (clones 51,Staub). Increase of trichoms and dry matter, length and diametre of trichoms and length of cells were measured; total volume of gas vacuoles and spectral absorption of the algal suspension between 380–730 nm were determined. The algae under discussion were attached to the speciesO. rubescens. Differences and accordances between the species studied andO. rubescens andO. prolifica as well, heterogeneity ofO. rubescens and variability of the characteristics ofO. rubescens are discussed.      

Maximally-efficient-generation approach in the dynamo theory

Abstract

We propose a method of derivation of global asymptotic solutions of the hydromagnetic dynamo problem at large magnetic Reynolds number. The procedure reduces to matching the local asymptotic forms for the magnetic field generated near individual extrema of generation strength. The basis of the proposed method, named here the Maximally-Efficient-Generation Approach (MEGA), is the assertion that properties of global asymptotic solutions of the kinematic dynamo are determined by the distribution of the generation strength near its leading extrema and by the number and distribution of the extrema.

The general method is illustrated by the global asymptotic solution of the α²-dynamo problem in a slab. The nature of oscillatory solutions revealed earlier in numerical simulations and the reasons for the dominance of even magnetic modes in slab geometry are clarified.

Applicability of the asymptotic solutions at moderate values of the asymptotic parameter is also discussed. We confirm this applicability using comparisons with complementary asymptotic expansions and numerical simulations. In particular, this justifies application of the MEGA solutions to estimation of the generation threshold.     

L in Potsdam,Seddin and Niemegk

Summary This paper deals with the deriving ofL based on the observations in Potsdam, Seddin and Niemegk. The calculation uses the investigations on finestructure ofSq published in previous papers. Two sunspot cycles were used, a quiet one and a disturbed one. The influence of the solar activity is clearly marked. The results are in good conformity with those ofS. Chapman andAd. Schmidt, but there are remarkable deviations in the results caused by using hourly values and not hourly mean values. These results are discussed, especially their mean deviations.Communication No. 173 of the Central Earth Physics Institute of the German Academy of Sciences at Berlin, GDR-15 Potsdam, Telegrafenberg.-This paper was presented at the XV General Assembly of IUGG, held in Moscow in August 1971.     

Simultaneous inversion of velocity structures and hypocentral locations: Application to the Friuli seismic area NE Italy

A layeredP- andS-wave velocity model is obtained for the Friuli seismic area using the arrival time data ofP- andS-waves from local earthquakes. A damped least-squares method is applied in the inversion.The data used are 994P-wave arrival times for 177 events which have epicenters in the region covered by the Friuli seismic network operated by Osservatorio Geofisico sperimentale (OGS) di Trieste, which are jointly inverted for the earthquake hypocenters andP-wave velocity model. TheS-wave velocity model is estimated on the basis of 978S-wave arrival times and the hypocenters obtained from theP-wave arrival time inversion. We also applied an approach thatP- andS-wave arrival time data are jointly used in the inversion (Roecker, 1982). The results show thatS-wave velocity structures obtained from the two methods are quite consistent, butP-wave velocity structures have obvious differences. This is apparent becauseP-waves are more sensitive to the hypocentral location thanS-waves, and the reading errors ofS-wave arrival times, which are much larger than those ofP-waves, bring large location errors in the joint inversion ofP- andS-wave arrival time. The synthetic data tests indicated that when the reading errors ofS-wave arrivals are larger than four times that ofP-wave arrivals, the method proposed in this paper seems more valid thanP- andS-wave data joint inversion. Most of the relocated events occurred in the depth range between 7 and 11 km, just above the biggest jump in velocity. This jump might be related to the detachment line hypothesized byCarulli et al. (1982). From the invertedP- andS-wave velocities, we obtain an average value 1.82 forV _p /V _s in the first 16 km depth.     

Principal horizontal stresses in Southern Africa

A review ofin situ stress measurements at eight regional localities in Africa south of the 15°S parallel shows that average directions of the horizontal pricipal stresses are N-S and E-W. These directions agree with principal stress orientations deduced from earthquake fault plane solutions. However, the maximum and minimum principal horizontal stresses are not consistently oriented parallel to either the N-S or E-W direction; they may vary within an individual region because of local geological structures and from region to region. At the sites within the Witwatersrand sediments (all at depths greater than 500 m) the maximum stress tends to lie NW-SE but at three of the four sites outside the Witwatersrand sediments (all at depths less than 500 m) this stress is oriented approximately N-S.The data reported here are compared with horizontal stresses predicted for Southern Africa bySolomon, Sleep andRichardson (1975) from various plate tectonic driving force models. The agreement between orientations is fair for all sites but only the deép sites in the Witwatersrand sediments have comparable stress magnitudes.     

A new measure of seismicity

Summary In this paper an attempt has been made to analyse the World shallow focus earth-quakes by the method ofGutenberg andRichter. Frequency-magnitude analysis of various earthquakes indicate that in the relation logN=a–b M, the ratio (b/a)^–1 satisfies fairly well the seismicity of a region and it is felt that this ratio may be used as a measure of seismicity for a given region.     

On waves generated by a moving pressure field,II: Cnoidal wave effects

Summary In a recent paperHunt andTanner [3]²) investigated the waves generated by a steadily moving two-dimensional pressure distribution, which was zero ahead of the disturbance and a constantp ₀, tehind it, these regions being joined smoothly by a cubic function. Only those solutions with supercritical flow in both regions were considered, these were found to lead to an asymmetric solitary wave.This result is now extended to take account of the possibility of subcritical flow in either or both the regions, that is when there is a cnoidal wave train either behind and or ahead of the main solitary wave crest.The wave profiles are determined by the iterative method employed in the previous paper. This together with the wave drag associated with each system is computed for various values ofp ₀/U ², where is the fluid density andU a typical velocity.     

Die Sonnenstrahlung und ihre Messung

Summary History and results of a 41/2-years-expedition to Argentine. A determination of the sun's «temperature» can only be given by the laws ofBoltzmann-Stefan andWien, because the temperature of the different layers is different. In the measurements of the sun's radiation the law ofBoltzmann-Stefan was introduced (T ⁴, where is a constant, andT the Kelvin-Temperature) while in the passed 100 years the difference between the sun's and the instruments radiation was taken as radiation, although this difference was arbitrariously variable with the instruments temperature. The effect of the vertical exchange of airmasses, on the radiation of the sun and the radiation of the air between the sun and the instrument was cleared. With these corrections one can not receive more as the difference between the so called solar constant and the albedo of the atmosphere. If the highest values are used (smallest albedo) the approximated value of the solar constant becomes 2.4, corresponding well to the value, derived from the supposed temperature of the sun.     

Predictors of the peak width for networks with exponential links

We investigate optimal predictors of the peak (S) and distance to peak (T) of the width function of drainage networks under the assumption that the networks are topologically random with independent and exponentially distributed link lengths. Analytical results are derived using the fact that, under these assumptions, the width function is a homogeneous Markov birth-death process. In particular, exact expressions are derived for the asymptotic conditional expectations ofS andT given network magnitudeN and given mainstream lengthH. In addition, a simulation study is performed to examine various predictors ofS andT, includingN, H, and basin morphometric properties; non-asymptotic conditional expectations and variances are estimated. The best single predictor ofS isN, ofT isH, and of the scaled peak (S divided by the area under the width function) isH. Finally, expressions tested on a set of drainage basins from the state of Wyoming perform reasonably well in predictingS andT despite probable violations of the original assumptions.     

Relazioni tra la velocità del vento e le caratteristiche del moto ondoso al largo e in costa

Summary The A. points out that the confirmation of the theory ofNeumann's significative waves, which differ from those ofSverdrup andMunk, would require observations of an accuracy not yet available. The existence of these waves would not change, anyhow,Sverdrup andMunk's conclusions out of the wind area.