A modeling study of acoustic propagation through movingshallow-water solitary wave packets     

Duda  T.F. Preisig  J.C. 《Oceanic Engineering, IEEE Journal of》1999,24(1):16-32

Propagation of 400-Hz sound through continental-shelf internal solitary wave packets is shown by numerical simulation to be strongly influenced by coupling of normal modes. Coupling in a packet is controlled by the mode coefficients at the point where sound enters the packet, the dimensions of the waves and packet, and the ambient depth structures of temperature and salinity. In the case of a moving packet, changes of phases of the incident modes with respect to each other dominate over the other factors, altering the coupling over time and thus inducing signal fluctuations. The phasing within a moving packet varies with time scales of minutes, causing coupling and signal fluctuations with comparable time scales. The directionality of energy flux between high-order acoustic modes and (less attenuated) low-order modes determines a gain factor for long-range propagation. A significant finding is that energy flux toward low-order modes through the effect of a packet near a source favoring high-order modes will give net amplification at distant ranges. Conversely, a packet far from a source sends energy into otherwise quiet higher modes. The intermittency of the coupling and of high-mode attenuation via bottom interaction means that signal energy fluctuations and modal diversity fluctuations at a distant receiver are complementary, with energy fluctuations suggesting a source-region packet and mode fluctuations suggesting a receiver-region packet. Simulations entailing 33-km propagation are used in the analyses, imitating the SWARM experiment geometry, allowing comparison with observations  相似文献   

Developments in solid earth geophysics volume 15: Proceedings of the Seventeenth Assembly of the European Seismological Commission Budapest, 24–29 August 1980. E. Bisztricsany and Gy. Szeidovitz (Editors). Elsevier Scientific Publishing Company,Amsterdam-Oxford-New York, 1983, XVIII + 689 pages,ISBN 0-444-99662-1.     

S.J. Duda 《Physics of the Earth and Planetary Interiors》1985,37(4):293-295

Various methods for the prediction of secular variation are tested by applying them to data for a single element at a single station. None of them is of any use for more than a few years.  相似文献   

Immune response of greenback flounder Rhombosolea tapirina after exposure to contaminated marine sediment and diet.     

J A Mondon  S Duda  B F Nowak 《Marine environmental research》2000,50(1-5):443-450

Non-specific immune response of greenback flounder, Rhombosolea tapirina, exposed to contaminated marine sediments was examined. Reference sediments from Port Sorell and contaminated sediments from Deceitful Cove, Tasmania, Australia were investigated. Hatchery-reared flounder were exposed to reference sediment, contaminated sediment or contaminated sediment and diet for 6 weeks. Phagocytic capacity and lysozyme response in flounder were examined on cessation of exposure trial. Significant differences were found in phagocytic capacity and lysozyme response between treatments. Exposure to contaminated sediment, irrespective of diet or benthic disturbance elicited inhibition of phagocytic efficiency in flounder. Disturbance of contaminated sediment stimulated lysozyme activity. The immune response in flounder indicates potential immunotoxicity of sediment from Deceitful Cove.  相似文献   

Coupled acoustic mode propagation through continental-shelfinternal solitary waves     

Preisig  J.C. Duda  T.F. 《Oceanic Engineering, IEEE Journal of》1997,22(2):256-269

Three techniques are used to investigate mode coupling as acoustic energy passes through continental-shelf internal solitary waves (ISW's). Results from all techniques agree. The waves considered here are single downward undulations of a thermocline layer separating upper and lower well-mixed layers. Two techniques are numerical: parabolic equation (PE) solution and a sudden approximation joining range-invariant regions at sharp vertical interfaces. The third technique is an analytic derivation of ISW scale lengths separating adiabatic (at large scale) and coupled-mode propagation. Results show that energy is exchanged between modes as ISW's are traversed. The sharp interface solutions help explain this in terms of spatially confined coupling and modal phase interference. Three regimes are observed: 1) for short ISW's, coupling upon wave entrance is reversed upon exit, with no net coupling; 2) for ISW scales of 75-200 m, modal phase alteration averts the exit reversal, giving net coupling; transparent resonances yielding no net coupling are also observed in this regime; and 3) for long ISW's, adiabaticity is probable but not universal. Mode refraction analysis for nonparallel acoustic-ISW alignment suggests that these two-dimensional techniques remain valid for 0° (parallel) to 65° (oblique) incidence, with an accordant ISW stretching  相似文献   

Numerical Modeling of the Observed Wiechert Seismograph Magnification     

M. Herak  I. Allegretti  D. Herak  S. J. Duda 《Pure and Applied Geophysics》1998,152(3):539-550

—The paper presents results of experiments designed to measure the actual dynamic magnification of the Wiechert 1000 kg horizontal seismometer when excited by seismic waves. This is accomplished by comparing 51 digital records of seismic events recorded by the Wiechert and a well calibrated reference seismometer. The results obtained indicate that the magnification of the Wiechert seismometer is influenced by the interaction of its mass and frame, especially for high frequencies. This interaction has been modeled by considering a system of two coupled pendulums, yielding a theoretical dynamic magnification curve which exhibits main features of the observed magnification. The dis crepancy between the nominal and the actual response of the Wiechert seismograph may lead to errors in studies involving spectral analyses of recorded seismograms, and to overestimation of local earth quake magnitudes.  相似文献   

Consistency of Magnitudes of the Largest Earthquakes of the First Half of the 20TH Century Determined on the Basis of Göttingen and Zagreb Wiechert Seismograms     

Ivo Allegretti  Davorka Herak  Marijan Herak  Seweryn J. Duda 《Studia Geophysica et Geodaetica》2000,44(1):13-25

The magnitudes (M _S , m _bP , m _bS ) of the largest historical earthquakes which occurred in the first half of the 20 ^th century, calculated on the basis of records of Wiechert horizontal seismographs in Göttingen (Germany) and Zagreb (Croatia), are compared with one another, as well as with the magnitudes reported in worldwide catalogues. Systematic trends are observed in the data regarding the temporal stability of magnitude estimations in Göttingen, as well as the apparent non-linearity of the instrument responsle in the case of the Wiechert seismograph in Zagreb. We were unable to clearly identify their causes – possible explanations include effects caused by the interaction of the seismometer's frame and mass, as well as local soil conditions, but nonhomogeneity of the reference catalogues cannot be ruled out. The results indicate that a careful re-examination and cross-checking of the reported magnitude figures for the earthquakes from the first half of the 20th century is required.  相似文献   

Determination of spectral properties of earthquakes from their magnitudes     

R. Nortmann  S. J. Duda 《Tectonophysics》1983,93(3-4)

Following the recommendation of the “IASPEI Commission on Magnitudes” from 1967, P-wave magnitudes of distant earthquakes are being computed with the aid of the calibration functions of Gutenberg and Richter (1956). With the development of the instrumental seismology, especially in view of the availability of broad-band recordings, the question arises whether the functions are still adequate.In this investigation new calibration functions for P- and S-waves are presented, which are not only dependent on epicentral distance and focal depth, but also on the period of the spectral component of the wave. The determination of calibration functions is based on the currently most plausible global models for the velocity and anelasticity distribution. Taking into account the effective bandwidth of the instruments employed, eventually leads to the so-called spectral magnitudes.From the spectral magnitudes m(T) , the energy density spectrum E(T) of the respective wave can readily be computed. The corresponding formula is E(T) = 10^{2m(T)− 1.4}, with E(T) in joules per hertz.  相似文献   

Spectral magnitude and seismic radiated energy computed from CDSN records     

Pei-Shan Chen  Seweryn J. Duda 《地震学报(英文版)》1993,6(4):803-811

We have employed 10 digital records and computed the spectral magnitude and the seismic radiated energy for 18 large earthquakes (M _s≥6) occurred in Eur-asian belt during 1986–1989. The nine digital stations (CD-SN) distribute all over China and one in Germany. The spectral magnitudes of various period have different stability among stations. The stability is better for maximum spectral magnitudemi and seismic radiated energyE, their differences among stations are smaller, especially for the stations where the ray path main penetrates the low mantle. But the stability of corner period is usually not good. The relation between seismic radiated energy and seismic moment magnitudeM _w is lg (E)=1.5Mw+c, wherec is a constant. The maximum spectral magnitudemi=M _w+0.1, it is consistant with theoretical prediction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 418–426, 1993. This work supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledge.  相似文献   

Integrated Reservoir Management for the Long Term-The Carpinteria Offshore Field     

E. M. Whitney  R. P. Kendall  M. R. Brickey  S. E. Coombs  C. A. Duda  V. K. Duda 《Marine Georesources & Geotechnology》1999,17(2):103-116

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2008年5月12日汶川地震谱震级及相关问题研究(英文)     

Seweryn J.Duda  Jaromir Jansky 《CT理论与应用研究》2009,18(2):15-23

基于P波和S波的谱震级特征对汶川地震进行了定量研究,可以看出P波和S波的最大谱震级出现在不同的周期上。对这一现象的构造物理意义进行了讨论,推测相对于P波而言,地震发生期间辐射的S波能量来自异常大的震源体积。选择部分全球地震的谱特征为背景,对汶川地震的体波谱震级特征进行了分析,结论是汶川地震的特征与其所处的周边环境是一致的。  相似文献