Attenuation of seismic waves near an explosion*

1954 ◽  
Vol 44 (3) ◽  
pp. 481-491
Author(s):  
B. F. Howell ◽  
E. K. Kaukonen
Keyword(s):  
Energy Loss ◽  
Surface Waves ◽  
Seismic Waves ◽  
Compressional Wave ◽  
Wave Surface ◽  
Shot Point ◽  
Weathered Layer

Abstract The energies of the first recorded pulses of seismic waves generated by a series of buried explosions is plotted as a function of distance from the shot point. At short distances the first pulse is a combination of the direct compressional wave, surface waves, and other pulses. Beyond 800 feet it is a pulse refracted at the bottom of the weathered layer. The refracted pulse has about 1/600 the energy of the direct pulse. The rate of attenuation of the two pulses is examined in an attempt to determine whether all the energy loss can reasonably be attributed to normal exponential absorption.

Seismic waves in a wedge

1975 ◽  
Vol 65 (6) ◽  
pp. 1697-1719
Author(s):  
Z. Alterman ◽  
R. Nathaniel
Keyword(s):  
Free Surface ◽  
Surface Waves ◽  
Particle Motion ◽  
Seismic Waves ◽  
Wedge Angle ◽  
Compressional Wave ◽  
Elastic Wedge ◽  
Compressional Wave Velocity ◽  
Quarter Plane ◽  
The Waves

abstract The equations for elastic-wave propagation caused by an explosive point source are solved, by a finite difference scheme, for the case of an elastic wedge, with free boundary. Varying the wedge angle shows that the amplitude of the motion, at the corner, increases as the wedge angle is decreased. The results indicate that for wedges with angles varying from 0° to 180°, the amplitude decreases with decreasing β/α (shear- to compressional-wave velocity). The corner of the wedge generates surface waves and the elliptical particle motion in the waves is analyzed. The particle motion is elliptic and the major axes of the ellipses are inclined at half the wedge angle to the free surface. The surface wave travels to the corner from where it is “transmitted” and reflected. Surface waves are shifted by 180° - θ after transmission. For the case of a quarter plane, we get the same result as Alterman and Loewenthal (1970).

What Is Tsunami Earthquake?

2021 ◽  
Author(s):  
Toshikazu Ebisuzaki
Keyword(s):  
Surface Waves ◽  
Seismic Waves ◽  
Submarine Landslides ◽  
Lower Efficiency ◽  
Tsunami Waves ◽  
Tsunami Earthquakes ◽  
Seismic Surface Waves ◽  
Tsunami Earthquake ◽  
Volcanic Islands ◽  
2004 Tsunami

Abstract A tsunami earthquake is defined as an earthquake which induces abnormally strong tsunami waves compared with its seismic magnitude (Kanamori 1972; Kanamori and Anderson 1975; Tanioka and Seno 2001). We investigate the possibility that the surface waves (Rayleigh, Love, and tsunami waves) in tsunami earthquakes are amplified by secondly submarine landslides, induced by the liquefaction of the sea floor due to the strong vibrations of the earthquakes. As pointed by Kanamori (2004), tsunami earthquakes are significantly stronger in longer waves than 100 s and low in radiation efficiencies of seismic waves by one or two order of magnitudes. These natures are in favor of a significant contribution of landslides. The landslides can generate seismic waves with longer period with lower efficiency than the tectonic fault motions (Kanamori et al 1980; Eissler and Kanamori 1987; Hasegawa and Kanamori 1987). We further investigate the distribution of the tsunami earthquakes and found that most of their epicenters are located at the steep slopes in the landward side of the trenches or around volcanic islands, where the soft sediments layers from the landmass are nearly critical against slope failures. This distribution suggests that the secondly landslides may contribute to the tsunami earthquakes. In the present paper, we will investigate the rapture processes determined by the inversion analysis of seismic surface waves of tsunami earthquakes can be explained by massive landslides, simultaneously triggered by earthquakes in the tsunami earthquakes which took place near the trenches.

scholarly journals Delineation of Weathered Layer Using Uphole and Surface Seismic Refraction Methods in Parts of Niger Delta, Nigeria

2021 ◽  
Vol 26 (1) ◽  
pp. 58-66
Author(s):  
Mfoniso Aka ◽  
Okechukwu Agbasi
Keyword(s):  
Niger Delta ◽  
Average Velocity ◽  
Seismic Refraction ◽  
Low Velocity ◽  
Engineering Structures ◽  
Experimental Proof ◽  
Seismic Surveys ◽  
Shot Point ◽  
Weathered Layer ◽  
Velocity Zone

Uphole and surface seismic refraction surveys were carried out in parts of the Niger Delta, Nigeria, to delineate weathering thickness and velocity associated with aweathered layer. A total of twelve uphole and surface seismic refraction surveyswere shot, computed and analyzed. The velocity of the uphole seismic refraction ranged from 344.8 to 680.3 m/s with a thickness of 5.45 to 13.35 m. Surface seismic refraction ranged from 326.6 to 670.2 m/s and 4.30 to 12.0 m, respectively. The average velocity and thickness ranged from 559.6 to 548.0 m/s and 9.43 to 8.63m with differences of 11.6 m/s and 0.83 m respectively. The VW/VS ratios ranged from 0.955 to 1.059. This indicates that the uphole velocity is higher than the surface refraction velocity leading to low VW/VS values. This is a direct experimental proof of a low velocity zone, confirming the weathered nature of the area. The results of both refraction methods are reliable; the differences in surface refraction values are due to shot point offsets. Based on these findings, it is recommended that shots for seismic surveys should be located above 15.0 m in the area to delineate the effects associated with weathered layers to ensure that will be competent to withstand engineering structures.  

Determination of the energy in body and surface waves

1959 ◽  
Vol 49 (1) ◽  
pp. 1-10
Author(s):  
John De Noyer
Keyword(s):  
Surface Waves ◽  
Seismic Waves ◽  
Numerical Results

Abstract Part II of this paper is concerned with the application of the methods for estimating the energy in seismic waves that were presented in Part I. Numerical results for the energy in the various phases of several earthquakes have been obtained.

High‐frequency reflections in granite? Delineation of the weathering front in granodiorite at Piñon Flat, California

Geophysics ◽  
1999 ◽  
Vol 64 (6) ◽  
pp. 1828-1835 ◽  
Author(s):  
Stanley J. Radzevicius ◽  
Gary L. Pavlis
Keyword(s):  
High Frequency ◽  
Seismic Waves ◽  
Lower Layer ◽  
Specular Reflection ◽  
Earth Model ◽  
Remarkable Feature ◽  
Reflection Data ◽  
Weathered Layer ◽  
High Frequency Seismic Waves ◽  
Seismic Lines

We analyze data from two orthogonal seismic lines 336 m in length collected at Piñon Flat, California, over weathered granodiorite bedrock. Each line was made up of 10 reversed segments 84 m in length. We analyzed the first arrivals from these data and found dramatic variations in velocity along the profiles. An upper layer (approximately 2-m thick) known from trenching to be composed of soil and sandy grus had measured velocities ranging from 400 to 700 m/s. Velocities inferred from refraction analysis of first arrivals of the reversed lines revealed a heterogeneous lower layer below the soil with measured velocities of 1600–2700 m/s by a depth of 15 m. We interpret these data to be measuring velocities of a deeply weathered unit characterized by granodiorite corestones embedded in a matrix of saprolite. The most remarkable feature of these data emerged from attempting to process the same data as reflection data. Simple bandpass filtering in the 250–400 Hz band revealed a bright, impulsive arrival with three characteristic properties: (1) irregular velocity moveout that is inconsistent with that expected from a layered earth model, (2) the arrival is at a nearly constant time‐depth on all data, and (3) the arrival tends to be followed by a ringing coda whose frequency varies from trace to trace. This arrival ties exactly with a velocity discontinuity measured in a borehole located on one of the profiles that we interpret as the base of the weathered layer. We suggest this arrival is a specular reflection from a weathering front that occurs along horizontal sheeting joints at a fixed depth below the surface. This surface acts as an effective mirror for high‐frequency seismic waves which are then channeled upward through an intact, high-Q path of unaltered blocks of granodiorite to define the observed signals at the surface.

Shear and compressional‐wave surface and downhole tests in Southern Louisiana

1983 ◽  
Author(s):  
Robert J. Corbin ◽  
David W. Bell ◽  
Stephen H. Danbom
Keyword(s):  
Compressional Wave ◽  
Wave Surface ◽  
Southern Louisiana

STUDIES ON SEISMIC WAVES: III. PROPAGATION OF ELASTIC WAVES IN THE NEIGHBORHOOD OF A FREE BOUNDARY

Geophysics ◽  
1947 ◽  
Vol 12 (1) ◽  
pp. 57-71 ◽  
Author(s):  
C. Y. Fu
Keyword(s):  
Surface Waves ◽  
Elastic Waves ◽  
Seismic Waves ◽  
Classical Method ◽  
Epicentral Distance ◽  
Harmonic Waves ◽  
Inhomogeneous Waves ◽  
Different Types ◽  
Propagation Of Elastic Waves ◽  
The Waves

Continuous and spherical harmonic waves are generated at an internal point of the medium. By use of the classical method of Sommerfeld, the different modes of propagation near a free surface after the arrival of the waves are examined. From the approximate evaluations of the integrals, it is found that in addition to the ordinary types of body and surface waves, there are also inhomogeneous waves and surface waves which are not of the Rayleigh type. The amplitude factors of these latter waves vary inversely as the square instead of as the square root of the epicentral distance. Altogether, there are not less than five different types of waves and they are obtained from integrations in the neighborhood of the singularities of the integrals.

scholarly journals Crustal structure of central Myanmar (Burma) By surface wave dispersion

MAUSAM ◽  
2022 ◽  
Vol 44 (4) ◽  
pp. 347-352
Author(s):  
S. N. BHATTACHARYA
Keyword(s):  
Surface Waves ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Seismic Waves ◽  
Digital Data ◽  
Low Velocity ◽  
Surface Wave Dispersion ◽  
Gangetic Plain ◽  
Indo Gangetic Plain ◽  
Group Velocities

Digital records of seismic waves observed at Seismic Research Observatory, Cheng Mai. Thailand have been analysed for two earthquakes in western Nepal. Digital data are processed by the floating filter and phase equalization methods to obtain surface waves free from noise. Group velocities of Love and Rayleigh waves are obtained by frequency time analysis of these noise free surface waves. The period of group velocities ranges from 17 to 62 sec for fundamental mode Rayleigh waves and from 17 to 66 sec for fundamental mode Love waves. The wave paths cross both central Myanmar (Burma) and the Indo-Gangetic plain. The group velocity data of surface waves across central Myanmar (Burma) have been obtained after correction of the data for the path across the Indo-Gangetic plain. Inversion of data gives the average crustal and subcrustal structure of central Myanmar (Burma). The modelled structure shows two separate sedimentary layers each of  8 km thick, The lower sedimentary layer forms the low velocity zone of the crust. The total thickness of central Myanmar (Burma) crust is found to be 55 km

Seeking an eye using several ears: cyclonic storms as heard by seismic arrays.

2021 ◽  
Author(s):  
Julián Pelaez ◽  
Dirk Becker ◽  
Céline Hadziioannou
Keyword(s):  
Surface Waves ◽  
Seismic Waves ◽  
Time Lapse ◽  
P Waves ◽  
Seismic Arrays ◽  
The North ◽  
Continental Shelves ◽  
Stationary Signals ◽  
Seismic Wavefield ◽  
Cyclonic Storms

<p>Under certain conditions, ocean surface gravity waves (SGW) interact with the seafloor underneath to trigger relatively faint but measurable seismic waves known as ocean microseisms. Cyclonic storms (<em>e.g.</em> hurricanes, typhoons) wandering over the ocean are major (non-stationary) sources of the former, thus opening the possibility of tracking and studying cyclones by means of their corresponding microseims.</p><p>For this purpose, we identified storm-related microseisms hidden in the ambient seismic wavefield via array processing. Polarization beamforming, a robust and well-known technique is implemented. The analyses hinge on surface waves (Love and Rayleigh) which, in contrast to P-waves, are stronger but only constrain direction of arrival (without source remoteness). We use a few land-based virtual seismic arrays surrounding the North Atlantic to investigate the signatures of major hurricanes in the microseismic band (0.05-0.16 Hz), in a joint attempt to continuously triangulate their tracks.</p><p>In general, a better correlation with the tracks was observed for surface waves in comparison to P waves. At the same frequency band, there is a good agreement between storm-related Love and retrograde Rayleigh wave signatures, suggesting a common amplification mechanism and co-located excitation area. However, the Love wavefield appears to be comparatively more diffuse and weaker than that of Rayleigh waves, which in turn produced the sharpest and most accurate trackings. </p><p>Our findings show that storm microseisms are intermittently excited with modulated amplitude at localized oceanic regions, particularly over the shallow continental shelves and slopes, having maximum amplitudes virtually independent of storm category. In most cases no detection was possible over deep oceanic regions, nor at distant arrays. Additionally, the rear quadrants and trailing swells of the cyclone provide the optimum SGW spectrum for the generation of microseisms, often shifted more than 500 km off the "eye". Occasionally, the passage of a cyclone near an island appears to trigger strong stationary signals lasting for a couple of days.</p><p>As a result of the aforementioned and added to the strong attenuation of storm microseisms, the inversion of tracks or physical properties of storms using a few far-field arrays is discontinuous in most cases, being reliable only if benchmark atmospheric and/or oceanic data is available for comparison. </p><p>Even if challenging due to the complexity of the coupled phenomena responsible for microseisms, the inversion of site properties, such as bathymetric parameters (<em>e.g.</em> depth, seabed geomorphology), near-bottom geology or SGW spectrum might be possible if storms are treated as natural sources in time-lapse ambient noise investigations. This will likely require near-field (land and underwater) observations using optimal arrays or dense, widespread sensor networks. Improved detection and understanding of ocean microseisms carries a great potential to contribute to mechanically coupled atmosphere-ocean-earth models. </p>

A note on the effect of ripple firing on the spectra of quarry shots

1963 ◽  
Vol 53 (1) ◽  
pp. 79-85
Author(s):  
D. E. Willis
Keyword(s):  
Surface Waves ◽  
Shear Wave ◽  
Seismic Waves

Abstract A series of controlled quarry shots were recorded at a distance of approximately 900 feet to ascertain the effect of ripple firing on amplitude and spectra of the seismic waves. A measurable reduction in the amplitude of compressional and shear wave was observed at some frequencies. This effect was not so pronounced for the surface waves.

Sign in / Sign up

Export Citation Format

Share Document