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.

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.

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.

Manipulation of seismic Rayleigh waves using a phase-gradient rubber metasurface

2020 ◽  
Vol 34 (13) ◽  
pp. 2050142
Author(s):  
Yanbin He ◽  
Tianning Chen ◽  
Xinpei Song
Keyword(s):  
Phase Shift ◽  
Rayleigh Wave ◽  
Surface Waves ◽  
Rayleigh Waves ◽  
Evanescent Waves ◽  
Smart Device ◽  
Phase Gradient ◽  
Seismic Surface Waves ◽  
Seismic Rayleigh Waves ◽  
Specific Phase

In this paper, a new method is proposed to manipulate seismic Rayleigh waves using phase-gradient metasurfaces. This highly compact artificial structure enables the anomalous refraction of Rayleigh waves according to the generalized Snell’s law (GSL). The soil-embedded metasurface is composed of only one column of commercial rubber blocks, which can provide an accurate phase shift to the Rayleigh wave. To verify the flexibility of this method, several metasurfaces are designed. Numerical results demonstrate that the Rayleigh waves can be focused, split, or converted into evanescent waves by using specific phase gradient configurations. The investigation also suggests the strong potential of metasurface as a smart device for shielding of seismic surface waves.

Normal modes of continental surface waves

1958 ◽  
Vol 48 (1) ◽  
pp. 33-49 ◽  
Author(s):  
Jack Oliver ◽  
Maurice Ewing
Keyword(s):  
Surface Waves ◽  
Normal Modes ◽  
Wave Dispersion ◽  
Low Velocity ◽  
Surface Wave Dispersion ◽  
Mode Dispersion ◽  
Seismic Surface Waves ◽  
Low Velocity Layer ◽  
Rayleigh Mode ◽  
Velocity Layer

Abstract When the path between epicenter and station traverses only continental structure, the dispersion of the entire train of directly arriving seismic surface waves can be explained as the result of normal mode propagation in a crust-mantle system in which the velocity increases in some manner with depth within the crust. At least four modes, the Rayleigh mode, Sezawa's M2 mode, and the first two Love waves, may appear prominently on the seismogram. The characteristics of the higher-mode dispersion curves permit the explanation of the Lg phase of Press and Ewing, B䳨's Lg1 and Lg2, and, in some cases, Caloi's Sa without recourse to a low-velocity layer in the crust or mantle. Speculation on changes in these curves for less simplified models indicates that the remaining cases of Sa as well as Leet's C or coupled wave may be explained by classical theory. The occurrence of the higher-mode waves is widespread; they are found on the four continents for which data are available. Higher-mode data, particularly when combined with information from the fundamental modes, make surface-wave dispersion, previously a useful tool, a much more potent method for the study of crustal structure.

The effect of surficial sedimentary layers on continental surface waves

1958 ◽  
Vol 48 (4) ◽  
pp. 339-354 ◽  
Author(s):  
Jack Oliver ◽  
Maurice Ewing
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Frequency Component ◽  
The United States ◽  
High Frequency Component ◽  
Detailed Knowledge ◽  
Mode Propagation ◽  
Long Distance ◽  
Period Range ◽  
Short Period

Abstract Surface waves in the 1/2-second to 12-second period range, recorded at several stations in eastern North America from the eastern Tennessee shock of June 23, 1957, are the bases for several deductions concerning the effect of sedimentary layers on continental surface wave propagation. These are: (1) The velocities of surface waves of the fundamental Love and Rayleigh modes having periods less than about 10 seconds may be strongly affected by sedimentary layers of average thickness. The decrease in velocity accounts, at least in part, for the prolongation of surface-wave trains in this period range when sedimentary layers of appreciable thickness have been traversed. (2) Higher-mode propagation for both types of surface waves is a possible explanation for the velocities, frequencies, and amplitudes of the phase Sg at moderate epicentral distances, and of its long-distance counterpart the high-frequency component of Lg. The lower-frequency components of Lg have been explained previously by other aspects of normal-mode propagation in the crust. (3) Study of dispersion of short-period surface waves can result in fairly detailed knowledge of velocity-depth relation within the sedimentary column and may also reveal information on anisotropy. (4) The results of this study must bear heavily on studies of microseism propagation. As an example, the increase of microseismic activity along the entire east coast of the United States when a storm moves onto the continental shelf may be attributed to channeling of the waves in the deep sedimentary trough beneath the shelf.

Propagation of PL waves across the United States

1964 ◽  
Vol 54 (1) ◽  
pp. 151-160
Author(s):  
Jack Oliver
Keyword(s):  
Rayleigh Waves ◽  
Velocity Dispersion ◽  
Wave Length ◽  
Seismic Refraction ◽  
The United States ◽  
Geometrical Spreading ◽  
Period Range ◽  
Long Period ◽  
Reflection Data ◽  
Phase Velocity Dispersion

abstract The two large Mexican earthquakes of May 1962 excited PL waves which were unusually well recorded by long period seismographs at a number of U. S. stations of the standardized network of the USC&GS. These data were used to make the first direct determinations of attenuation and of phase velocity dispersion of PL waves in the crust-mantle wave guide. When the effects of dispersion and geometrical spreading are removed, the Q for PL waves in the period range of 35 to 50 seconds is about 10, in contrast to a Q of about 150 for Rayleigh waves of the same wave length. There is a clear dependence of PL dispersion on crustal structure, with data for western profiles indicating crustal thicknesses greater than those for eastern profiles. Such information is complementary to information on dispersion of other types of surface waves and to seismic refraction and reflection data and can provide additional constraint on models of the crust-mantle system.

Surface-wave dispersion analysis in Mexico City

1995 ◽  
Vol 85 (4) ◽  
pp. 1116-1126
Author(s):  
Francisco J. Chávez-García ◽  
Jaime Ramos-Martínez ◽  
Evangelina Romero-Jiménez
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Ground Motion ◽  
Mexico City ◽  
Rayleigh Waves ◽  
Strong Motion ◽  
Clay Layer ◽  
Period Range ◽  
Wave Trains ◽  
Refraction Data

Abstract In this article, we present an observational investigation of ground motion at Mexico City focused on surface waves. Our purpose is 2-fold; first, to understand incident ground motion during the great Michoacán earthquake of 19 September 1985, and second, to characterize surface waves propagating in the lake-bed zone. To this end we analyze the strong-motion records obtained at Mexico City for the large (MS = 8.1) earthquake of 19 September 1985. It is shown that, in the low-frequency range, we observe the Rayleigh fundamental mode in both the vertical and the radial components, and the Love fundamental mode in the transverse component at all the strong-motion stations. The vertical component also shows the first higher mode of Rayleigh waves. We use a very broadband record obtained at station CU for the smaller (MS = 6.7) earthquake of 14 May 1993 to verify that the dispersion computed from the model of Campillo et al. (1989) represents well the average surface-wave propagation between the coast and Mexico City in the 7- to 10-sec period range. We use this result to assign absolute times to the strong-motion records of the Michoacán event. This allowed us to identify additional wave trains that propagate laterally in directions other than great circle in the 3- to 5-sec period range. These wave trains are identified as Love waves. In a second analysis, we study a set of refraction data obtained during a small-scale (250 m) experiment on the virgin clay of the lake-bed zone. Phase-velocity dispersion curves for several modes of Rayleigh waves are identified in the refraction data and inverted to obtain an S-wave velocity profile. This profile is used as the uppermost layering in a 2D model of Mexico City valley. The results of numerical simulation show that surface waves generated by lateral finiteness of the clay layer suffer large dispersion and attenuation. We conclude that surface waves generated by the lateral heterogeneity of the upper-most stratigraphy very significantly affect ground motion near the edge of the valley, but their importance is negligible for distances larger than 1.5 km from the edge. Thus, locally generated surface waves propagating through the clay layer cannot explain late arrivals observed for the 1985 event. We suggest that the long duration of strong motion is due to the interaction between lateral propagation of waves guided by deep layers (1 to 4 km) and the surficial clay layer. This interaction is possible by the coincidence of the dominant frequency of the uppermost layers and the frequency of the deeply guided waves.

scholarly journals Interpretation of deformed ionograms induced by vertical ground motion of seismic Rayleigh waves and infrasound in the thermosphere

2016 ◽  
Vol 34 (2) ◽  
pp. 271-278 ◽  
Author(s):  
Takashi Maruyama ◽  
Kamil Yusupov ◽  
Adel Akchurin
Keyword(s):  
Ground Motion ◽  
Acoustic Waves ◽  
Rayleigh Waves ◽  
Ionospheric Disturbances ◽  
Vertical Ground Motion ◽  
Short Period ◽  
Seismic Surface Waves ◽  
Chile Earthquake ◽  
Fluctuation Amplitude ◽  
Vertical Ground

Abstract. The vertical ground motion of seismic surface waves launches acoustic waves into the atmosphere and induces ionospheric disturbances. Disturbances due to Rayleigh waves near the short-period Airy phase appear as wavy fluctuations in the virtual height of an ionogram and have a multiple-cusp signature (MCS) when the fluctuation amplitude is increased. An extremely developed MCS was observed at Kazan, Russia, after the 2010 M 8.8 Chile earthquake. The ionogram exhibited steep satellite traces for which the virtual heights increased rapidly with frequency starting near the top of cusps and continuing for 0.1–0.2 MHz. This complicated ionogram was analyzed by applying a ray tracing technique to the radio wave propagation in the ionosphere that was perturbed by acoustic waves. Acoustic wavefronts were inclined by the effects of finite Rayleigh wave velocity and sound speed in the thermosphere. The satellite echo traces were reproduced by oblique returns from the inclined wavefronts, in addition to the nearly vertical returns that are responsible for the main trace.

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