SHEAR‐WAVE DETECTION IN NEAR‐SURFACE SEISMIC REFRACTION STUDlES

Geophysics ◽  
1966 ◽  
Vol 31 (5) ◽  
pp. 981-983 ◽  
Author(s):  
James H. Whitcomb
Keyword(s):  
Physical Properties ◽  
Shear Wave ◽  
Shear Waves ◽  
Seismic Refraction ◽  
Geological Survey ◽  
Near Surface ◽  
Wave Detection

The U. S. Geological Survey, on behalf of the National Aeronautics and Space Administration, has begun investigations designed to relate the data obtained from seismic refraction profiles to the physical properties of lunar analog earth materials. The velocity of shear waves is a significant property, but the recording of these waves presented a serious problem.

Shear‐wave splitting in cross‐hole surveys: Modeling

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 57-65 ◽  
Author(s):  
Enru Liu ◽  
Stuart Crampin ◽  
David C. Booth
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Pore Space ◽  
Shear Waves ◽  
Shear Wave Splitting ◽  
Surface Layers ◽  
Near Surface ◽  
Crustal Rocks ◽  
Wave Splitting ◽  
Almost All

Shear‐wave splitting, diagnostic of some form of effective seismic anisotropy, is observed along almost all near‐vertical raypaths through the crust. The splitting is caused by propagation through distributions of stress‐aligned vertical parallel fluid‐filled cracks, microcracks, and preferentially oriented pore space that exist in most crustal rocks. Shear waves have severe interactions with the free surface and may be seriously disturbed by the surface and by near‐surface layers. In principle, cross‐hole surveys (CHSs) should be free of much of the near‐surface interference and could be used for investigating shear waves at higher frequencies and greater resolution along shorter raypaths than is possible with reflection surveys and VSPs. Synthetic seismograms are examined to estimate the effects of vertical cracks on the behavior of shear waves in CHS experiments. The azimuth of the CHS section relative to the strike of the cracks is crucial to the amount of information about seismic anisotropy that can be extracted from such surveys. Interpretation of data from only a few boreholes located at azimuths chosen from other considerations is likely to be difficult and inconclusive. Application to interpreting acoustic events generated by hydraulic pumping is likely to be more successful.

Geostatistical simulation for geophysical applications—Part II: Geophysical modeling

Geophysics ◽  
1990 ◽  
Vol 55 (11) ◽  
pp. 1441-1446 ◽  
Author(s):  
P. N. Shive ◽  
T. Lowry ◽  
D. H. Easley ◽  
L. E. Borgman
Keyword(s):  
Physical Properties ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Three Dimensional ◽  
Companion Paper ◽  
Geostatistical Simulation ◽  
Near Surface ◽  
Geophysical Modeling ◽  
Karst Environment ◽  
Geophysical Surveys

A companion paper (this issue) describes a method for producing three‐dimensional simulations of physical properties for different geologic situations. Here we create a simulation for a particular case, which is a near‐surface (<80 ft deep) description of a karst environment. We simulate seismic velocity, density, resistivity, and the dielectric constant for this situation. We then conduct (in the computer) hypothetical geophysical surveys at the surface of the model. These surveys are seismic refraction, microgravity, dc resistivity, and ground‐probing radar. Physical properties appropriate for cavities are then entered in the model. Repeating the geophysical surveys over the model with cavities provides a convenient method of evaluating their potential for cavity detection. Anomalies produced by normal variations in physical properties may simulate or obscure anomalies from target features. More data about the correlation of physical properties, particularly in the horizontal directions, will be required to evaluate this problem properly.

scholarly journals Shear-wave detection of asymmetric c-axis fabrics in the GISP2 ice core, Greenland

1994 ◽  
Vol 40 (136) ◽  
pp. 491-496 ◽  
Author(s):  
S. Anandakrishnan ◽  
J.J. Fltzpatrick ◽  
R.B. Alley ◽  
A.J. Gow ◽  
D.A. Meese
Keyword(s):  
Shear Wave ◽  
Ice Core ◽  
Shear Waves ◽  
Compressional Wave ◽  
Optical Methods ◽  
Ultrasound Technique ◽  
Optical Techniques ◽  
The Core ◽  
Wave Detection ◽  
Wave Data

Abstractc-axis fabrics of the GISP2 ice core from central Greenland have been measured rapidly and accurately in the field, using both compressional and shear waves generated by an inexpensive, commercially available, “idiot-proof” device. Compressional-wave data were collected at 10 m intervals for the upper 2250 m of the ice sheet and show progressive clustering of c axes toward the vertical with increasing depth but no large steps at climatic boundaries in the core. The degree of clustering measured by ultrasound agrees closely with that measured using traditional optical techniques but the ultrasound technique is easier and faster than optical methods. A slight asymmetry in the c-axis clustering is revealed by the shear-wave data and increases with increasing depth, indicating that deformation is not symmetric about the vertical at the site.

Physics of shear-waves propagating in saturated and unsaturated soils: new potential for monitoring soil dynamics and stability

2021 ◽  
Author(s):  
Ranajit Ghose
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Unsaturated Soils ◽  
Shear Waves ◽  
Soil Layer ◽  
Time Lapse ◽  
Soil Dynamics ◽  
Near Surface

&lt;p&gt;Shear waves are uniquely informative because of their vector nature &amp;#8211; with both polarization and propagation of shear waves being useful sources of information, their sensitivity to &lt;em&gt;in-situ&lt;/em&gt; stress and grain-to-grain contact, and also because of the low velocity of shear waves in relatively soft formations - offering short wavelength and hence high resolution. Decimetre-scale resolution found in shear-wave reflection data in soft soil has resulted in new application possibilities. Medium anisotropy extracted from multi-component shear-wave data has provided information on natural symmetries in small-strain rigidity and/or stress in the shallow subsurface, which are caused by factors that are of great interest to the engineers. AVO response of shear waves at near-surface soil-layer boundaries has also proven to be useful for extracting local information in the subsoil.&lt;/p&gt;&lt;p&gt;In the present research we have looked at the sensitivity of shear-wave velocity and the underlying physics in both saturated and unsaturated near-surface soils, and if these can practically be used for monitoring soil dynamics and soil stability. Time-lapse changes in shear-wave velocity could be used to monitor changes in &lt;em&gt;in-situ&lt;/em&gt; stress in the saturated sands. More recently, we have developed methodologies to invert time-lapse shear-wave velocity information together with geo-electrical information to obtain&lt;em&gt; in-situ&lt;/em&gt; values of water saturation and suction in different partially saturated soil units. Incorporation of this information in a spatially varying sense is imperative in order to make assessment of stability of unsaturated soil slopes subjected to rainfall, modelling flooding and sediment flows due to increased surface runoff and erosion, sustainable agriculture through in-situ water moisture monitoring, and modelling pollutant transport through soils.&lt;/p&gt;

High-frequency borehole seismograms recorded in the San Jacinto Fault zone, Southern California. Part 1. Polarizations

1991 ◽  
Vol 81 (4) ◽  
pp. 1057-1080 ◽  
Author(s):  
Richard C. Aster ◽  
Peter M. Shearer
Keyword(s):  
Shear Wave ◽  
Fault Zone ◽  
Particle Motion ◽  
Southern California ◽  
Shear Waves ◽  
P Wave ◽  
S Wave ◽  
Near Surface ◽  
San Jacinto Fault ◽  
San Jacinto Fault Zone

Abstract Two borehole seismometer arrays (KNW-BH and PFO-BH) have been established in the Southern California Batholith region of the San Jacinto Fault zone by the U.S. Geological Survey. The sites are within 0.4 km of Anza network surface stations and have three-component seismometers deployed at 300 m depth, at 150 m depth, and at the surface. Downhole horizontal seismometers can be oriented to an accuracy of about 5° using regional and near-regional initial P-wave particle motions. Shear waves recorded downhole at the KNW-BH indicate that the strong alignment of initial S-wave particle motions previously observed at the (surface) KNW Anza site (KNW-AZ) is not generated in the near-surface weathered layer. The KNW-BH surface instrument, which sits atop a highly weathered zone, displays a significantly different (≈ 20°) initial S-wave polarization direction from that observed downhole and at KNW-AZ, which is bolted to an outcrop. Although downhole initial shear-wave particle motion directions are consistent with a shear-wave splitting hypothesis, observations of orthogonally polarized slow shear waves are generally elusive, even in seismograms recorded at 300 m. A cross-correlation measure of the apparent relative velocities of Sfast and Sslow horizontally polarized S waves suggests shallow shear-wave anisotropy, consistent with the observed initial S-wave particle motion direction, of 2.3 ± 1.7 per cent between 300 and 150 m and 7.5 ± 3.5 per cent between 150 and 0 m.

scholarly journals Shear-wave detection of asymmetric c-axis fabrics in the GISP2 ice core, Greenland

1994 ◽  
Vol 40 (136) ◽  
pp. 491-496 ◽  
Author(s):  
S. Anandakrishnan ◽  
J.J. Fltzpatrick ◽  
R.B. Alley ◽  
A.J. Gow ◽  
D.A. Meese
Keyword(s):  
Shear Wave ◽  
Ice Core ◽  
Shear Waves ◽  
Compressional Wave ◽  
Optical Methods ◽  
Ultrasound Technique ◽  
Optical Techniques ◽  
The Core ◽  
Wave Detection ◽  
Wave Data

Abstractc-axis fabrics of the GISP2 ice core from central Greenland have been measured rapidly and accurately in the field, using both compressional and shear waves generated by an inexpensive, commercially available, “idiot-proof” device. Compressional-wave data were collected at 10 m intervals for the upper 2250 m of the ice sheet and show progressive clustering ofcaxes toward the vertical with increasing depth but no large steps at climatic boundaries in the core. The degree of clustering measured by ultrasound agrees closely with that measured using traditional optical techniques but the ultrasound technique is easier and faster than optical methods. A slight asymmetry in thec-axis clustering is revealed by the shear-wave data and increases with increasing depth, indicating that deformation is not symmetric about the vertical at the site.

scholarly journals Near surface shear wave velocity in Bucharest, Romania

2008 ◽  
Vol 8 (6) ◽  
pp. 1299-1307 ◽  
Author(s):  
M. von Steht ◽  
B. Jaskolla ◽  
J. R. R. Ritter
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Compressional Wave ◽  
Seismic Zone ◽  
Surface Shear ◽  
Near Surface ◽  
Surface Shear Wave

Abstract. Bucharest, the capital of Romania with nearly 2 1/2 million inhabitants, is endangered by the strong earthquakes in the Vrancea seismic zone. To obtain information on the near surface shear-wave velocity Vs structure and to improve the available microzonations we conducted seismic refraction measurements in two parks of the city. There the shallow Vs structure is determined along five profiles, and the compressional-wave velocity (Vp) structure is obtained along one profile. Although the amount of data collected is limited, they offer a reasonable idea about the seismic velocity distribution in these two locations. This knowledge is useful for a city like Bucharest where seismic velocity information so far is sparse and poorly documented. Using sledge-hammer blows on a steel plate and a 24-channel recording unit, we observe clear shear-wave arrivals in a very noisy environment up to a distance of 300 m from the source. The Vp model along profile 1 can be correlated with the known near surface sedimentary layers. Vp increases from 320 m/s near the surface to 1280 m/s above 55–65 m depth. The Vs models along all five profiles are characterized by low Vs (<350 m/s) in the upper 60 m depth and a maximum Vs of about 1000 m/s below this depth. In the upper 30 m the average Vs30 varies from 210 m/s to 290 m/s. The Vp-Vs relations lead to a high Poisson's ratio of 0.45–0.49 in the upper ~60 m depth, which is an indication for water-saturated clayey sediments. Such ground conditions may severely influence the ground motion during strong Vrancea earthquakes.

DETERMINATION OF THE PHYSICAL PROPERTIES OF COMPLEXLY CONSTRUCTED MEDIA USING NEAR-SURFACE CROSSWELL METHOD

2019 ◽  
pp. 13-20 ◽  
Author(s):  
H. Guliyev ◽  
Kh. Aghayev ◽  
F. Mehraliyev ◽  
E. Ahmadova
Keyword(s):  
Physical Properties ◽  
Poisson’S Ratio ◽  
Seismic Anisotropy ◽  
Water Saturation ◽  
Shear Waves ◽  
Practical Importance ◽  
Poisson's Ratio ◽  
High Porosity ◽  
Reservoir Pressure ◽  
Near Surface

In case when the upper part of the medium has complex geological structure and geodynamic processes occur in it, the necessity of these data increases in projecting of the object under construction. Purpose. Studying of acoustic, elastic and anisotropic properties of the upper part of section of complicatedly constructed geological media. Methodology. Seismic observations are conducted in shallow wells in the areas of construction objects located in various seismogeological conditions by NSCW (Near-Surface Cross Well testing) method. Field seismic records are processed. Kinematic and dynamic parameters of pressure and differently polarized shear waves are determined. Thin-layered one-dimensional models of physical properties of the medium are created and interpreted on the basis of nonlinear theory of elastodynamics. Results. It is determined that the medium with high porous, water saturated rocks and anomalous high reservoir pressure has anomalous low value of velocities and gradient of their increase with depth. When this medium was re-examined after deep piles were built there, the overestimated seismic velocities are obtained, which is explained by a decrease in the section of anomalously high reservoir pressure and, accordingly, the porosity of the rocks after piles were built. When the hollowness is increased in unsaturated pebble rocks, the negative value of Poisson's ratio is obtained on the standard method. Seismic anisotropy related with the direction of the grains packing of the rocks is revealed on velocities of shear waves. The change of property of rocks on depth is manifested clearer on frequencies of waves than on their amplitudes. Scientific novelty. The elasticity moduli of the 3rd order are determined which are more sensible to variability of nonlinear elastic properties of rocks of the medium than the moduli of the 2nd order. The values of Poisson's ratio are recalculated for one and the same rocks located in different conditions of rock pressure on the basis of nonclassical theory of deformation. Practical importance. The obtained results can be applied to study the media characterized by complex seismogeological hydrodynamic conditions with clay-sandy rocks of high porosity and water saturation.

scholarly journals Near-surface seismic refraction tomography and MASW for site characterization in Phuentsholing, Bhutan Himalaya

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Raju Sarkar ◽  
Sreevalsa Kolathayar ◽  
Dowchu Drukpa ◽  
Kinley Choki ◽  
Shrijana Rai ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Seismic Refraction ◽  
P Wave ◽  
Response Analysis ◽  
Soil Parameters ◽  
Near Surface ◽  
Engineering Construction ◽  
Refraction Tomography

AbstractIt is essential to understand the soil characteristics of the subsurface layers for any engineering construction. In difficult terrains like hilly areas, conventional methods of investigation are expensive and difficult to conduct. It calls for nondestructive testing methods to get reliable estimates of subsurface properties. In the present study, seismic refraction tomography (SRT) technique and multichannel analysis of surface waves (MASW) methods were carried out along five selected profiles in Phuentsholing region of Bhutan Himalaya. The profile length ranges from 37 to 81.5 m, and depth of imaging down to 10 m. While the SRT data imaged the P-wave velocity (Vp) structures, the MASW imaged the shear wave velocity (Vs) structures. The P-wave images provide a fair knowledge of geological layers, while the MASW images provide S-wave velocity structures (Vs). These results are useful to estimate soil parameters, like the density, Poisson’s ratio, Young’s modulus, shear modulus, N-value and the ultimate bearing capacity. The seismic images reveal the presence of sand, sandy clay, gravels and shale layers below the selected sites. Bhutan Himalayas being seismically vulnerable, the obtained results in terms of shear wave velocity were accustomed to categorize the sites as per NEHRP site classes, and a ground response analysis was performed to determine the reliable amplification factors. From the study, it is suggested that the engineering construction is feasible at all the sites except in one site, where an indication of saturated soil is observed which is vulnerable for liquefaction, and ground needs to be improved before construction at that site.

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