scholarly journals Observations of multiple seismic events

1964 ◽  
Vol 54 (1) ◽  
pp. 19-39
Author(s):  
W. L. Pilant ◽  
L. Knopoff
Keyword(s):  
Amplitude Ratio ◽  
Multipath Propagation ◽  
Wave Train ◽  
Seismic Surface Waves ◽  
Derived Properties ◽  
Beat Phenomenon ◽  
Wave Trains ◽  
The Individual ◽  
Comparable Magnitude ◽  
Resultant Wave

abstract Two or more dispersed wave trains each with constant amplitude will interfere giving a resultant wave train which is amplitude modulated, if the individual waves have their principal energies in a common frequency band and if the trains arrive with time separations small compared to their total length. The dispersive characteristics of the trains need not be the same. If the component trains are of comparable magnitude, the modulation due to interference becomes significant and a “beat” phenomenon occurs. Multiple trains of dispersed seismic surface waves may occur because of a temporal and/or spatial distribution at the source or because of multipath propagation. Each of these causal mechanisms influences the amplitude and phase spectra of the resultant wave train; derived properties such as phase velocities and amplitude ratios are also influenced. In the case of multipath propagation, wavelength dependent time delays may occur. Two cases of twin earthquakes are analyzed, and the significant features of interference are demonstrated. In one case, estimates are obtained for the amplitude ratio and time delay of the second shock with respect to the first. The interpretation of seismograms and spectra influenced by multiple events is discussed.

Phase-matched filters: Application to the study of Love waves

1979 ◽  
Vol 69 (1) ◽  
pp. 27-44
Author(s):  
Tom Goforth ◽  
Eugene Herrin
Keyword(s):  
Rayleigh Waves ◽  
Matched Filter ◽  
Multipath Propagation ◽  
Group Velocity Dispersion ◽  
Wave Train ◽  
Seismic Signal ◽  
Love Waves ◽  
Complex Spectrum ◽  
Matched Filters ◽  
Wave Trains

abstract Seismic surface waves are usually composed of overlapping wave trains representing multipath propagation. A first task in the analysis of such waves is to identify and separate the various component wave trains so that each can be analyzed separately. Phase-matched filters are a class of linear filters in which the Fourier phase of the filter is made equal to that of a given signal. Herrin and Goforth (1977) described an iterative technique which can be used to find a phase-matched filter for a particular component of a seismic signal. Application of the filters to digital records of Rayleigh waves allowed multiple arrivals to be identified and removed, and allowed recovery of the complex spectrum of the primary wave train along with its apparent group-velocity dispersion curve. A comparable analysis of Love waves presents additional complications. Love waves are contaminated by both Love and Rayleigh multipathing and by primary off-axis Rayleigh energy. In the case of explosions, there is much less energy generated as Love waves than as Rayleigh waves. The applicability of phase-matched filtering to Love waves is demonstrated by its use on earthquakes occurring in the Norwegian Sea and near Iceland and on a nuclear explosion in Novaya Zemlya. Despite severe multipathing in two of the three events, the amplitude and phase of each of the primary Love waves were recovered without significant distortion.

Stability of periodic waves in shallow water

1974 ◽  
Vol 66 (1) ◽  
pp. 81-96 ◽  
Author(s):  
P. J. Bryant
Keyword(s):  
Shallow Water ◽  
Wave Train ◽  
Periodic Wave ◽  
Fundamental Wave ◽  
Cnoidal Waves ◽  
Margin Of Stability ◽  
Fundamental Wavelength ◽  
Stokes Waves ◽  
Wave Trains ◽  
Permanent Shape

Waves of small but finite amplitude in shallow water can occur as periodic wave trains of permanent shape in two known forms, either as Stokes waves for the shorter wavelengths or as cnoidal waves for the longer wavelengths. Calculations are made here of the periodic wave trains of permanent shape which span uniformly the range of increasing wavelength from Stokes waves to cnoidal waves and beyond. The present investigation is concerned with the stability of such permanent waves to periodic disturbances of greater or equal wavelength travelling in the same direction. The waves are found to be stable to infinitesimal and to small but finite disturbances of wavelength greater than the fundamental, the margin of stability decreasing either as the fundamental wave becomes more nonlinear (i.e. contains more harmonics), or as the wavelength of the periodic disturbance becomes large compared with the fundamental wavelength. The decreasing margin of stability is associated with an increasing loss of spatial periodicity of the wave train, to the extent that small but finite disturbances can cause a form of interaction between consecutive crests of the disturbed wave train. In such a case, a small but finite disturbance of wavelength n times the fundamental wavelength converts the wave train into n interacting wave trains. The amplitude of the disturbance subharmonic is then nearly periodic, the time scale being the time taken for repetitions of the pattern of interactions. When the disturbance is of the same wavelength as the permanent wave, the wave is found to be neutrally stable both to infinitesimal and to small but finite disturbances.

On a uniformly valid model for surface wave interaction

1993 ◽  
Vol 247 ◽  
pp. 589-601 ◽  
Author(s):  
Yehuda Agnon
Keyword(s):  
Surface Wave ◽  
Water Waves ◽  
Wave Train ◽  
Wave Interaction ◽  
Shallow Water Waves ◽  
First Order ◽  
Near Resonance ◽  
Wave Trains ◽  
Velocity Changes ◽  
Forced Waves

Nonlinear interaction of surface wave trains is studied. Zakharov's kernel is extended to include the vicinity of trio resonance. The forced wave amplitude and the wave velocity changes are then first order rather than second order. The model is applied to remove near-resonance singularities in expressions for the change of speed of one wave train in the presence of another. New results for Wilton ripples and the drift current and setdown in shallow water waves are readily derived. The ideas are applied to the derivation of forced waves in the vicinity of quartet and quintet resonance in an evolving wave field.

Shear-coupled higher mode seismic surface waves

1967 ◽  
Vol 57 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Stuart Crampin
Keyword(s):  
Surface Waves ◽  
Wave Motion ◽  
S Wave ◽  
Higher Modes ◽  
Mode Wave ◽  
Mode Dispersion ◽  
Seismic Surface Waves ◽  
Wave Trains ◽  
Group Velocities

abstract Some higher mode wave trains with irregular dispersion, and some anomalies in the S-wave motion at epicentral distances less than 30°, are shown to be shear-coupled higher modes. The group velocities along the higher mode portions of the paths agree well with observations of direct higher mode dispersion in Scandinavia.

scholarly journals Tropical Cyclogenesis Associated with Rossby Wave Energy Dispersion of a Preexisting Typhoon. Part I: Satellite Data Analyses*

2006 ◽  
Vol 63 (5) ◽  
pp. 1377-1389 ◽  
Author(s):  
Tim Li ◽  
Bing Fu
Keyword(s):  
Rossby Wave ◽  
Satellite Data ◽  
Wave Energy ◽  
Large Scale ◽  
Wave Train ◽  
Vertical Shear ◽  
Energy Dispersion ◽  
Data Analyses ◽  
Wave Trains ◽  
Rossby Wave Train

Abstract The structure and evolution characteristics of Rossby wave trains induced by tropical cyclone (TC) energy dispersion are revealed based on the Quick Scatterometer (QuikSCAT) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) data. Among 34 cyclogenesis cases analyzed in the western North Pacific during 2000–01 typhoon seasons, six cases are associated with the Rossby wave energy dispersion of a preexisting TC. The wave trains are oriented in a northwest–southeast direction, with alternating cyclonic and anticyclonic vorticity circulation. A typical wavelength of the wave train is about 2500 km. The TC genesis is observed in the cyclonic circulation region of the wave train, possibly through a scale contraction process. The satellite data analyses reveal that not all TCs have a Rossby wave train in their wakes. The occurrence of the Rossby wave train depends to a certain extent on the TC intensity and the background flow. Whether or not a Rossby wave train can finally lead to cyclogenesis depends on large-scale dynamic and thermodynamic conditions related to both the change of the seasonal mean state and the phase of the tropical intraseasonal oscillation. Stronger low-level convergence and cyclonic vorticity, weaker vertical shear, and greater midtropospheric moisture are among the favorable large-scale conditions. The rebuilding process of a conditional unstable stratification is important in regulating the frequency of TC genesis.

On the scattering of short surface waves by a finite dock

1968 ◽  
Vol 64 (4) ◽  
pp. 1109-1129 ◽  
Author(s):  
F. G. Leppington
Keyword(s):  
Wave Train ◽  
Normal Incidence ◽  
Great Depth ◽  
Travelling Wave ◽  
Reflection And Transmission ◽  
Large Wave ◽  
Transmission Coefficients ◽  
Weakly Coupled ◽  
Wave Trains ◽  
Induced Velocity

AbstractA sinusoidal travelling wave-train is at normal incidence upon a two-dimensional finite dock fixed on the surface of a body of water of great depth, and the problem investigated herein is that of finding the limiting form of the induced velocity potential for short waves. Of particular interest are the amplitudes of the wave-trains reflected and transmitted towards infinity by such an obstacle. The potential is expressed as a sum of coupled semi-infinite dock potentials, whence results a pair of weakly coupled integral equations for the solution. This formulation of the problem is shown to be amenable to an approximate solution for large wave-numbers, and the first few terms are derived in formal expansions for the reflection and transmission coefficients.

Broadcast Distance of the Mutual Display Call in the Emperor Penguin

Behaviour ◽  
1991 ◽  
Vol 119 (3-4) ◽  
pp. 302-316 ◽  
Author(s):  
Patrice Robisson
Keyword(s):  
Background Noise ◽  
Individual Recognition ◽  
Emperor Penguin ◽  
Scattering Medium ◽  
Fundamental Frequencies ◽  
Aptenodytes Forsteri ◽  
Medium Range ◽  
Beat Phenomenon ◽  
The Individual ◽  
Individual Information

AbstractIn the colonial emperor penguin Aptenodytes forsteri, the broadcast distance of the mutual display call (the distance over which the individual information conveyed by the call is transmitted) was determined. The variables measured were (1) the sound amplitude that averaged 94.8 dB SPL for birds facing toward the microphone and 85.7 dB SPL for birds facing away, (2) the sound attenuation that decreased with about 6 dB per doubling distance, (3) the ratio of the signal to the background noise of the colony which was 20-25 dB during the rearing period of chicks, and (4) the degradation of the signal structure by the scattering medium (penguin bodies) and distance, which affected the timbre, but not the two fundamental frequencies of the call that produced a beat phenomenon. This distance, 4-7 m indicates that the call is transmitted at short- or medium-range, and corresponds closely to the distance covered between two stops where a parent in search for its chick calls. The beat phenomenon undegraded by the scattering medium and distance is likely to serve individual recognition, assuming there is a relationship between the broadcast distance and the functional structure of emperor penguin call.

scholarly journals Exploring the Tropically Excited Arctic Warming Mechanism with Station Data: Links between Tropical Convection and Arctic Downward Infrared Radiation

2016 ◽  
Vol 73 (3) ◽  
pp. 1143-1158 ◽  
Author(s):  
Matthew D. Flournoy ◽  
Steven B. Feldstein ◽  
Sukyoung Lee ◽  
Eugene E. Clothiaux
Keyword(s):  
Water Vapor ◽  
Rossby Wave ◽  
Infrared Radiation ◽  
Wave Train ◽  
Tropical Convection ◽  
The Arctic ◽  
Water Vapor Flux ◽  
Arctic Warming ◽  
Vapor Flux ◽  
Wave Trains

Abstract The Tropically Excited Arctic Warming (TEAM) mechanism ascribes warming of the Arctic surface to tropical convection, which excites poleward-propagating Rossby wave trains that transport water vapor and heat into the Arctic. A crucial component of the TEAM mechanism is the increase in downward infrared radiation (IR) that precedes the Arctic warming. Previous studies have examined the downward IR associated with the TEAM mechanism using reanalysis data. To corroborate previous findings, this study examines the linkage between tropical convection, Rossby wave trains, and downward IR with Baseline Surface Radiation Network (BSRN) downward IR station data. The physical processes that drive changes in the downward IR are also investigated by regressing 300-hPa geopotential height, outgoing longwave radiation, water vapor flux, ERA-Interim downward IR, and other key variables against the BSRN downward IR at Barrow, Alaska, and Ny-Ålesund, Spitsbergen. Both the Barrow and the Ny-Ålesund station downward IR anomalies are preceded by anomalous tropical convection and poleward-propagating Rossby wave trains. The wave train associated with Barrow resembles the Pacific–North America teleconnection pattern, and that for Ny-Ålesund corresponds to a northwestern Atlantic wave train. It is found that both wave trains promote warm and moist advection from the midlatitudes into the Arctic. The resulting water vapor flux convergence, multiplied by the latent heat of vaporization, closely resembles the regressed ERA-Interim downward IR. These results suggest that the combination of warm advection, latent heat release, and increased cloudiness all contribute toward an increase in downward IR.

scholarly journals NATURAL WAVE TRAINS: DESCRIPTION AND REPRODUCTION

1978 ◽  
Vol 1 (16) ◽  
pp. 16 ◽  
Author(s):  
H. Lundgren ◽  
S.E. Sand
Keyword(s):  
Numerical Models ◽  
Wave Train ◽  
Three Dimensional ◽  
Correct Description ◽  
Linear Superposition ◽  
Natural Wave ◽  
Wave Trains ◽  
Steep Waves ◽  
Deterministic Description ◽  
The Waves

In many applications there is a great need for a correct description of the natural, irregular three-dimensional sea and its reproduction in physical and numerical models. Because of the tremendous difficulties inherent in the nonlinearities, the science of coastal engineering is still very far from this ultimate goal. Indeed, the scope of this paper is comparatively very modest: To describe and reproduce natural, irregular two-dimensional waves, i.e. waves propagating in one direction in a flume. In addition, this scope is fulfilled only by assuming linear superposition of Fourier terms. As opposed to the usual spectral description, the deterministic description presented here does not eliminate the phase information in the wave train recorded. Because of the nonlinearities, however, the linear deterministic description invariably degenerates with the distance travelled by the waves. It appears though from the present paper that the degeneration is fairly slow even for rather steep waves.

scholarly journals Precursory atmospheric circulations with Rossby wave trains leading to Eurasian extreme cold events

2021 ◽  
Author(s):  
Wenqin zhuo ◽  
Fei Huang ◽  
Ruichang Ding ◽  
Jin Luo
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Wave Train ◽  
Teleconnection Pattern ◽  
Boreal Winter ◽  
Formation Mechanisms ◽  
Baffin Bay ◽  
Atmospheric Circulations ◽  
Westerly Jet ◽  
Wave Trains

Abstract This work examines precursory atmospheric circulations with various wave trains contributing to extreme cooling over central Eurasia in boreal winter from 1979-2016 based on the ERA-Interim dataset. The empirical orthogonal function (EOF) method is used to classify the anomalous sea level pressure field averaged in two weeks prior to extreme cooling. Based on the classification, three types of precursory atmospheric circulation patterns are named according to the origins of wave trains, and their formation mechanisms are revealed as well . Type1: Baffin Bay-origin pattern, which forms in the downstream development of Rossby wave packets generated from the downward stratospheric energy transmission over the Baffin Bay. Type2: Pacific-origin pattern, similar to a Eurasian (EU) teleconnection pattern, arises at the exit area of the westerly jet in the central North Pacific where cyclonic shear exists; then it develops along the northerly westerly jet over the North Atlantic, which may act as a waveguide to the Eurasian continent. Type 3: Atlantic-origin, manifests as the negative phase of type 2, consistent with the Scandinavian (SCAND) pattern, which may results from the air-sea interaction induced by the warm anomaly of sea surface temperature in the middle of North Atlantic. In conclusion, the three types of precursory atmospheric wave train patterns that bring extreme cooling to Eurasia possess diverse disturbing sources and development mechanisms. The results, which are investigated based on a quasi-biweekly time scale , deepen our understanding of the atmospheric genesis of extreme weather and have specific indicative significance to improve the technique of extended forecast.

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