Short-period oceanic surface waves of the rayleigh and first shear modes

1958 ◽  
Vol 39 (3) ◽  
pp. 482 ◽  
Author(s):  
Jack Oliver ◽  
Maurice Ewing
Keyword(s):  
Surface Waves ◽  
Oceanic Surface ◽  
Short Period ◽  
Shear Modes

The effect of oceanic sediments on surface-wave propagation

1975 ◽  
Vol 65 (6) ◽  
pp. 1531-1552
Author(s):  
Donald J. Weidner
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Rayleigh Waves ◽  
Propagation Path ◽  
Surface Wave Propagation ◽  
Oceanic Surface ◽  
Oceanic Sediments ◽  
Wave Phase Velocity ◽  
Short Period ◽  
Mid Atlantic Ridge

abstract Several characteristics of oceanic surface waves can be altered by the presence of low rigidity sediments along the propagation path. Love and Rayleigh waves from mid-Atlantic ridge earthquakes bear many effects of oceanic sediments. The general absence of these surface waves for periods shorter than about 15 sec can be attributed to either attenuation or scattering in thin sediments. Thin sediments also disperse short-period Love waves. Sediments whose thickness exceeds about 2 km are responsible for removing surface-wave energy with periods up to 40 sec. These sediments also alter the particle motion of Rayleigh waves and are responsible for a complicated dispersion relation. These thick sediments substantially reduce the surface-wave phase velocity at periods in excess of 100 sec.

On the nature of oceanic seismic surface waves with predominant periods of 6 to 8 seconds

1961 ◽  
Vol 51 (3) ◽  
pp. 437-455
Author(s):  
Jack Oliver ◽  
James Dorman
Keyword(s):  
Surface Waves ◽  
Deep Sea ◽  
Rayleigh Waves ◽  
Seismic Refraction ◽  
Normal Modes ◽  
Quantitative Agreement ◽  
Period Range ◽  
Oceanic Surface ◽  
Short Period ◽  
Seismic Surface Waves

Abstract The train of normally-dispersed, short-period, oceanic surface waves, commonly identified by the near-sinusoidal nature of all three components of ground motion in the period range of about 6 to 8 seconds, is shown to correspond to propagation in the first Love and first shear normal modes. Theoretical dispersion curves which agree with the observed dispersion of these short-period waves, as well as with dispersion of Rayleigh waves and Love waves of longer periods, are obtained for layered models of the oceanic crust which are consistent with results of seismic refraction studies. In order to obtain good quantitative agreement between theory and observation, it is essential that the effect of the small but finite rigidity of the deep-sea sedimentary layer be included in the calculations.

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.

scholarly journals Automated detection and association of surface waves

1994 ◽  
Vol 37 (3) ◽  
Author(s):  
R. G. North ◽  
C. R. D. Woodgold
Keyword(s):  
Surface Waves ◽  
Group Velocity ◽  
Rayleigh Waves ◽  
Arrival Time ◽  
Narrow Band ◽  
Broad Band ◽  
Detection Algorithm ◽  
Automated Detection ◽  
Short Period ◽  
Group Velocities

An algorithm for the automatic detection and association of surface waves has been developed and tested over an 18 month interval on broad band data from the Yellowknife array (YKA). The detection algorithm uses a conventional STA/LTA scheme on data that have been narrow band filtered at 20 s periods and a test is then applied to identify dispersion. An average of 9 surface waves are detected daily using this technique. Beamforming is applied to determine the arrival azimuth; at a nonarray station this could be provided by poIarization analysis. The detected surface waves are associated daily with the events located by the short period array at Yellowknife, and later with the events listed in the USGS NEIC Monthly Summaries. Association requires matching both arrival time and azimuth of the Rayleigh waves. Regional calibration of group velocity and azimuth is required. . Large variations in both group velocity and azimuth corrections were found, as an example, signals from events in Fiji Tonga arrive with apparent group velocities of 2.9 3.5 krn/s and azimuths from 5 to + 40 degrees clockwise from true (great circle) azimuth, whereas signals from Kuriles Kamchatka have velocities of 2.4 2.9 km/s and azimuths off by 35 to 0 degrees. After applying the regional corrections, surface waves are considered associated if the arrival time matches to within 0.25 km/s in apparent group velocity and the azimuth is within 30 degrees of the median expected. Over the 18 month period studied, 32% of the automatically detected surface waves were associated with events located by the Yellowknife short period array, and 34% (1591) with NEIC events; there is about 70% overlap between the two sets of events. Had the automatic detections been reported to the USGS, YKA would have ranked second (after LZH) in terms of numbers of associated surface waves for the study period of April 1991 to September 1992.

Short-period surface waves across the Iberian Peninsula area

1979 ◽  
Vol 56 (1-2) ◽  
pp. 65
Author(s):  
G. Payo ◽  
J.A. Pérez
Keyword(s):  
Surface Waves ◽  
Iberian Peninsula ◽  
Short Period

scholarly journals Evaluating Monin-Obukhov Scaling in the Unstable Oceanic Surface Layer

2020 ◽  
Author(s):  
Zhihua Zheng ◽  
Ramsey R. Harcourt ◽  
Eric A. D’Asaro
Keyword(s):  
Surface Layer ◽  
Surface Waves ◽  
Scaling Laws ◽  
Similarity Theory ◽  
Vertical Mixing ◽  
Temperature Gradients ◽  
Langmuir Turbulence ◽  
Near Surface ◽  
Oceanic Surface ◽  
Using Data

AbstractMonin-Obukhov Similarity Theory (MOST) provides important scaling laws for flow properties in the surface layer of the atmosphere and has contributed to most of our understanding of the near-surface turbulence. The prediction of near-surface vertical mixing in most operational ocean models is largely built upon this theory. However, the validity of MOST in the upper ocean is questionable due to the demonstrated importance of surface waves in the region. Here we examine the validity of MOST in the statically unstable oceanic surface layer, using data collected from two open ocean sites with different wave conditions. The observed vertical temperature gradients are found to be about half of those predicted by MOST. We hypothesize this is attributable to either the breaking of surface waves, or Langmuir turbulence generated by the wave-current interaction. Existing turbulence closure models for surface wave breaking and for Langmuir turbulence are simplified to test these two hypotheses. Although both models predict reduced temperature gradients, the simplified Langmuir turbulence model matches observations more closely, when appropriately tuned.

scholarly journals Low-Frequency Earthquakes along the Ryukyu Islands Triggered by Teleseismic Earthquakes

2021 ◽  
Author(s):  
Ayumi Kinjo ◽  
Mamoru Nakamura
Keyword(s):  
Surface Waves ◽  
Low Frequency ◽  
Stress Sensitivity ◽  
Peak Ground Velocity ◽  
Ryukyu Islands ◽  
Plate Interface ◽  
Okinawa Island ◽  
Short Period ◽  
Ryukyu Arc ◽  
The Ryukyu Islands

Abstract Tremors and low-frequency earthquakes (LFEs), which occur in the plate interface, can provide useful information about the state of aseismic stress transfer in mega-earthquake fault zones. We estimated the distribution of stress sensitivity in the subducted plate interface by using triggered LFEs. Specifically, we detected LFEs in the Ryukyu Trench triggered by the surface waves of large teleseismic earthquakes by using the waveform records of broadband and short-period seismometers installed in the Ryukyu Arc. We selected a total of 45 teleseismic earthquakes with magnitudes of more than 7.5, which occurred between 2004 and 2017, for the analysis. We could detect the triggered LFEs for five teleseismic earthquakes. Then, we determined the hypocenters of LFEs by using the relative arrival times of LFEs for each station. The LFEs were distributed in the south of Okinawa Island and the Yaeyama area. Moreover, they were distributed around the source fault of the slow slip events. These were almost the same as the position of LFEs accompanying very low-frequency earthquakes (VLFEs). However, the epicenters of the triggered LFEs were concentrated near the locations of the most active LFE clusters accompanying VLFEs. This suggests that the sensitivity for inducing LFEs was higher near the most active clusters of the LFEs accompanying the VLFEs. The amplitudes of the triggered LFEs were proportional to the peak ground velocity of the surface waves. This indicates that the LFEs accompanying VLFEs are activated by stress acceleration in the Yaeyama and Okinawa areas and the triggered LFEs observed in these areas can be a result of the activation of the ambient tremors due to increased stress.

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