Observation and Theory of Strain–Infrasound Coupling during Ground-Coupled Infrasound Generated by Rayleigh Waves in the Longitudinal Valley (Taiwan)

2020 ◽  
Vol 110 (6) ◽  
pp. 2991-3003
Author(s):  
Alexandre Canitano
Keyword(s):  
Atmospheric Pressure ◽  
Rayleigh Waves ◽  
Seismic Waves ◽  
Seismic Velocity ◽  
Pressure Fluctuations ◽  
Radial Distance ◽  
Period Range ◽  
Intrinsic Nature ◽  
Strain Waves ◽  
Cross Correlation Analysis

ABSTRACT In this study, changes in atmospheric pressure recorded by absolute microbarometers operating in the Longitudinal Valley (Taiwan) during the passing seismic waves from strong earthquakes (Mw≥6) are systematically analyzed during the 2007–2019 period. Using a continuous wavelet transform analysis, local infrasound signals are detected for 23% of the events (21 events out of 89), with Mw ranging from 6.0 to 9.1 at a radial distance of 15 to about 4000 km from the central Longitudinal Valley. Infrasound signals are observed in the period range from about 1 to 20 s; they have maximal amplitudes ranging from 0.4 to 20 Pa and initiate predominantly during the passage of Rayleigh waves. The atmospheric pressure response to dilatational strain waves during seismoacoustic disturbances is investigated using collocated borehole strainmeter stations, and dynamic interactions between signals are characterized using a sliding windowed time-lagged cross-correlation analysis. The infrasound response shows a phase shift of −60° to −100°, with respect to the dilatation strain signal with a coupling factor of 0.002–0.006  Pa/nϵ for most of the cases (62%). Whereas acoustic pressure fluctuations are generated instantaneously by the vertical seismic velocity, the phase delay is related to the intrinsic nature of the dilatational strain. Observational strain–infrasound coupling parameters are in close agreement with theoretical estimates in the case of ground-coupled acoustic signals generated by Rayleigh waves. The study represents the first attempt to analyze ground-coupled infrasonic waves with strain waves and illustrates the potential of collocated strainmeter–microbarometer stations for basic seismoacoustic studies.

The Stochastic Parametric Mechanism for Growth of Wind-Driven Surface Water Waves

2008 ◽  
Vol 38 (4) ◽  
pp. 862-879 ◽  
Author(s):  
Brian F. Farrell ◽  
Petros J. Ioannou
Keyword(s):  
Surface Water ◽  
Growth Rates ◽  
Atmospheric Pressure ◽  
Water Waves ◽  
Wave Amplitude ◽  
Pressure Fluctuations ◽  
Theoretical Understanding ◽  
Wave Growth ◽  
Atmospheric Pressure Fluctuations ◽  
Surface Water Waves

Abstract Theoretical understanding of the growth of wind-driven surface water waves has been based on two distinct mechanisms: growth due to random atmospheric pressure fluctuations unrelated to wave amplitude and growth due to wave coherent atmospheric pressure fluctuations proportional to wave amplitude. Wave-independent random pressure forcing produces wave growth linear in time, while coherent forcing proportional to wave amplitude produces exponential growth. While observed wave development can be parameterized to fit these functional forms and despite broad agreement on the underlying physical process of momentum transfer from the atmospheric boundary layer shear flow to the water waves by atmospheric pressure fluctuations, quantitative agreement between theory and field observations of wave growth has proved elusive. Notably, wave growth rates are observed to exceed laminar instability predictions under gusty conditions. In this work, a mechanism is described that produces the observed enhancement of growth rates in gusty conditions while reducing to laminar instability growth rates as gustiness vanishes. This stochastic parametric instability mechanism is an example of the universal process of destabilization of nearly all time-dependent flows.

An algorithm for automated tsunami warning in French Polynesia based on mantle magnitudes

1989 ◽  
Vol 79 (4) ◽  
pp. 1177-1193
Author(s):  
Jacques Talandier ◽  
Emile A. Okal
Keyword(s):  
Rayleigh Wave ◽  
Seismic Moment ◽  
Rayleigh Waves ◽  
French Polynesia ◽  
Tsunami Warning ◽  
Period Range ◽  
Wave Duration ◽  
T Wave ◽  
The Moment ◽  
Historical References

Abstract We have developed a new magnitude scale, Mm, based on the measurement of mantle Rayleigh-wave energy in the 50 to 300 sec period range, and directly related to the seismic moment through Mm = log10M0 − 20. Measurements are taken on the first passage of Rayleigh waves, recorded on-scale on broadband instruments with adequate dynamical range. This allows estimation of the moment of an event within minutes of the arrival of the Rayleigh wave, and with a standard deviation of ±0.2 magnitude units. In turn, the knowledge of the seismic moment allows computation of an estimate of the high-seas amplitude of a range of expectable tsunami heights. The latter, combined with complementary data from T-wave duration and historical references, have been integrated into an automated procedure of tsunami warning by the Centre Polynésien de Prévention des Tsunamis (CPPT), in Papeete, Tahiti.

Short-period seismic noise

1967 ◽  
Vol 57 (1) ◽  
pp. 55-81
Author(s):  
E. J. Douze
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Body Waves ◽  
Deep Hole ◽  
Period Range ◽  
Short Period ◽  
The Subject ◽  
Hole Arrays

abstract This report consists of a summary of the studies conducted on the subject of short-period (6.0-0.3 sec period) noise over a period of approximately three years. Information from deep-hole and surface arrays was used in an attempt to determine the types of waves of which the noise is composed. The theoretical behavior of higher-mode Rayleigh waves and of body waves as measured by surface and deep-hole arrays is described. Both surface and body waves are shown to exist in the noise. Surface waves generally predominate at the longer periods (of the period range discussed) while body waves appear at the shorter periods at quiet sites. Not all the data could be interpreted to define the wave types present.

Ellipticity of Rayleigh waves recorded in the Midwest

1977 ◽  
Vol 67 (2) ◽  
pp. 369-382
Author(s):  
John L. Sexton ◽  
A. J. Rudman ◽  
Judson Mead
Keyword(s):  
Local Structure ◽  
Rayleigh Waves ◽  
Signal To Noise Ratio ◽  
Interference Effects ◽  
Signal To Noise ◽  
Period Range ◽  
Model Studies ◽  
Single Station ◽  
Special Value ◽  
The Time Domain

Abstract Measurements of ellipticity of Rayleigh waves recorded in the U.S. Midwest have been examined for azimuth dependence, effects of interference, and repeatability, as well as the hypothesis that a single station may be used to determine local structure. Time- and frequency-domain analyses were performed for each event, with more consistent results from the time-domain method. Results indicate that for the period range of 10 to 50 sec, ellipticity depends primarily upon local structure and does not exhibit significant azimuthal dependence. Most ellipticity values for a given period are repeatable within 5 per cent of other measured values from all source regions, with the greatest deviation being about 10 per cent. The cause of the deviations is attributed to interfering waves and/or poor signal-to-noise ratios. Interference effects result in scatter in ellipticity values. An ellipticity peak in the period range of 18 to 22 sec has variable magnitude for different events, depending upon the amount of interference present and the signal-to-noise ratio. Interference effects also manifest themselves as sharp decreases in group-velocity observations even after filtering. Model studies show that ellipticity peaks can exist, which are due to the layered structure and not necessarily to interference effects. Ellipticity measurements (10- to 50-sec-period range) from a single station are useful for determination of a crustal model for the vicinity of the recording station, but should be used in conjunction with other available geophysical and geological data. Ellipticity measurements are shown to be of special value for model determination in areas with sedimentary layering, a result in agreement with the Boore-Toksöz 1969) study.

Analysis of Rayleigh-wave multipath propagation at LASA

1970 ◽  
Vol 60 (5) ◽  
pp. 1701-1731 ◽  
Author(s):  
Jack Capon
Keyword(s):  
Rayleigh Waves ◽  
Multipath Propagation ◽  
Continental Margins ◽  
Period Range ◽  
Analysis Technique ◽  
High Resolution Analysis ◽  
Resolution Analysis ◽  
Propagation Paths ◽  
Using Data ◽  
Almost All

Abstract An investigation has been made of the multipath propagation of Rayleigh waves by using data obtained from the large aperture seismic array (LASA). The use of the LASA in conjunction with a high-resolution analysis technique provides a greater angular resolution and accuracy than was previously possible for the analysis of the multipath propagation. Measurements have been made of this phenomenon for the Rayleigh waves of 26 events distributed at various azimuths and distances from LASA. On the bas of these measurements reasonably good conjectures are made concerning the actual propagation paths for groups in the 20- to 40-sec period range. It is shown that in almost all cases these propagation paths can be associated with refractions and reflections at the continental margins.

Membrane transport activity and ultradian ion flux oscillations associated with cell cycle of Thraustochytrium sp.

2001 ◽  
Vol 28 (2) ◽  
pp. 87 ◽  
Author(s):  
Lana Shabala ◽  
Sergey Shabala ◽  
Tom Ross ◽  
Tom McMeekin
Keyword(s):  
Nutritional Status ◽  
Membrane Transport ◽  
Close Association ◽  
Essential Element ◽  
Ion Flux ◽  
Transport Activity ◽  
Period Range ◽  
Bathing Medium ◽  
Zoospore Release ◽  
Cross Correlation Analysis

Membrane transport activity associated with growth and nutritional status of a marine microheterotroph Thraustochytrium sp. was studied using non-invasive ion-selective slowly vibrating microelectrodes (the MIFE technique). Net fluxes of H + , Ca 2+ and Na + underwent regular changes as the cell progressed from the zoospore to sporangium stages of development. The most pronounced change was a decrease in the net H + influx, which we suggest could be associated with the changes in cytoskeletal organization required for cell cleavage and zoospore release. As cell development progressed from the zoospore stage towards maturity, non-damping endogenous ultradian oscillations (period range of several minutes) became evident. At the sporangium stage, as many as 85% of cells possessed oscillatory membrane transport activity. It is suggested that ultradian ion flux oscillations in Thraustochytrium sp. may be causally linked with cell developmental processes. Discrete Fourier transform and cross-correlation analysis revealed a close association between oscillatory patterns of H + and Na + fluxes. The possibility that these oscillations result from the rhythmical activity of a Na + /H + co-transporter located at the plasma membrane of Thraustochytrium sp. is considered. Oscillations in net Ca 2+ flux were apparently not linked to those in H+ and Na + , and are believed to be due to some other physiological processes. Periods of net H + and Na + flux oscillations were strongly dependent on the external Na + concentrations in the bathing medium. As sodium is considered to be an essential element in Thraustochytrium sp., it is suggested that the functional role of such ultradian oscillations may be their involvement in the frequency-encoding mechanism that provides developing cells with information about environment, and nutritional status in particular.

Crosscoherence-based interferometry for the retrieval of first arrivals and subsequent tomographic imaging of differential weathering

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. Q37-Q48 ◽  
Author(s):  
Joachim Place ◽  
Deyan Draganov ◽  
Alireza Malehmir ◽  
Christopher Juhlin ◽  
Chris Wijns
Keyword(s):  
Seismic Waves ◽  
Seismic Velocity ◽  
Signal To Noise Ratio ◽  
Seismic Profile ◽  
Seismic Interferometry ◽  
Near Surface ◽  
Tomographic Images ◽  
Traveltime Tomography ◽  
Seismic Methods ◽  
Source Signal

Exhumation of crust exposes rocks to weathering agents that weaken the rocks’ mechanical strength. Weakened rocks will have lower seismic velocity than intact rocks and can therefore be mapped using seismic methods. However, if the rocks are heavily weathered, they will attenuate controlled-source seismic waves to such a degree that the recorded wavefield would become dominated by ambient noise and/or surface waves. Therefore, we have examined the structure of differential weathering by first-break traveltime tomography over a seismic profile extending approximately 3.5 km and acquired at a mining site in Zambia using explosive sources and a source based on the swept-impact seismic technique (SIST). Seismic interferometry has been tested for the retrieval of supervirtual first arrivals masked by uncorrelated noise. However, use of crosscorrelation in the retrieval process makes the method vulnerable to changes in the source signal (explosives and SIST). Thus, we have developed a crosscoherence-based seismic-interferometry method to tackle this shortcoming. We investigate the method’s efficiency in retrieving first arrivals and, simultaneously, correctly handling variations in the source signal. Our results illustrate the superiority of the crosscoherence- over crosscorrelation-based method for retrieval of the first arrivals, especially in alleviating spurious ringyness and in terms of the signal-to-noise ratio. These benefits are observable in the greater penetration depth and the improved resolution of the tomography sections. The tomographic images indicate isolated bodies of higher velocities, which may be interpreted as fresh rocks embedded into a heavily weathered regolith, providing a conspicuous example of differential weathering. Our study advances the potential of seismic methods for providing better images of the near surface (the critical zone).

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