scholarly journals Frequency dependent attenuation of seismic waves for Delhi and surrounding area, India

2015 ◽  
Vol 58 (2) ◽  
Author(s):  
Babita Sharma ◽  
Prasantha Chingtham ◽  
Anup K. Sutar ◽  
Sumer Chopra ◽  
Haldhar P. Shukla
Keyword(s):  
Seismic Waves ◽  
Quality Factors ◽  
P Waves ◽  
Frequency Dependent ◽  
S Waves ◽  
Intrinsic Attenuation ◽  
Attenuation Parameter ◽  
Coda Normalization Method ◽  
Coda Normalization ◽  
Single Backscattering Model

<p align="left">The attenuation properties of Delhi &amp; surrounding region have been investigated using 6<em>2</em> local earthquakes recorded at nine stations. The frequency dependent quality factors <em>Q</em><em><sub>a</sub></em> (using P-waves) and <em>Q</em><em><sub>b</sub></em> (using S-waves) have been determined using the coda normalization method. Quality factor of coda-waves (<em>Q<sub>c</sub></em>) has been estimated using the single backscattering model in the frequency range from 1.5 Hz to 9 Hz. Wennerberg formulation has been used to estimate <em>Q<sub>i</sub></em> (intrinsic attenuation parameter) and <em>Q<sub>s</sub></em> (scattering attenuation parameter) for the region. The values <em>Q</em><em><sub>a</sub>, Q</em><em><sub>b, </sub>Q<sub>c, </sub>Q<sub>i</sub> and Q<sub>s</sub></em> estimated are frequency dependent in the range of 1.5Hz-9Hz. Frequency dependent relations are estimated as <em>Q</em><em><sub>a</sub>=52f<sup>1.03</sup>, Q</em><em><sub>b</sub>=98f<sup>1.07</sup> and Q<sub>c</sub>=158f<sup>0.97</sup></em>. <em>Q<sub>c</sub></em> estimates lie in between the values of <em>Q<sub>i</sub></em> and <em>Q<sub>s</sub></em> but closer to <em>Q<sub>i</sub></em> at all central frequencies. Comparison between <em>Q<sub>i</sub> </em>and <em>Q<sub>s</sub></em> shows that intrinsic absorption is predominant over scattering for Delhi and surrounding region. </p>

Intrinsic and Scattering Attenuations in the Crust of the Racha Region, Georgia

2019 ◽  
Vol 14 (02) ◽  
pp. 2050006
Author(s):  
Ia Shengelia ◽  
Nato Jorjiashvili ◽  
Tea Godoladze ◽  
Zurab Javakhishvili ◽  
Nino Tumanova
Keyword(s):  
Time Window ◽  
Frequency Range ◽  
Quality Factors ◽  
Lapse Time ◽  
Intrinsic Attenuation ◽  
Total Attenuation ◽  
Relative Contribution ◽  
Normalization Methods ◽  
Coda Normalization ◽  
Back Scattering

Three hundred and thirty-five local earthquakes were processed and the attenuation properties of the crust in the Racha region were investigated using the records of seven seismic stations. We have estimated the quality factors of coda waves ([Formula: see text]) and the direct [Formula: see text] waves ([Formula: see text]) by the single back scattering model and the coda normalization methods, respectively. The Wennerberg’s method has been used to estimate relative contribution of intrinsic ([Formula: see text]) and scattering ([Formula: see text]) attenuations in the total attenuation. We have found that [Formula: see text] and [Formula: see text] parameters are frequency-dependent in the frequency range of 1.5–24[Formula: see text]Hz. [Formula: see text] values increase both with respect to lapse time window from 20[Formula: see text]s to 60[Formula: see text]s and frequency. [Formula: see text] and [Formula: see text] parameters are nearly similar for all frequency bands, but are smaller than [Formula: see text]. The obtained results show that the intrinsic attenuation has more significant effect than scattering attenuation in the total attenuation. The increase of [Formula: see text] with lapse time shows that the lithosphere becomes more homogeneous with depth.

scholarly journals Converted‐wave seismic exploration: Applications

Geophysics ◽  
2003 ◽  
Vol 68 (1) ◽  
pp. 40-57 ◽  
Author(s):  
Robert R. Stewart ◽  
James E. Gaiser ◽  
R. James Brown ◽  
Don C. Lawton
Keyword(s):  
Seismic Waves ◽  
Seismic Exploration ◽  
Fracture Density ◽  
Converted Wave ◽  
P Waves ◽  
Near Surface ◽  
S Waves ◽  
Subsurface Fluid ◽  
Processing Techniques ◽  
Gas Bearing

Converted seismic waves (specifically, downgoing P‐waves that convert on reflection to upcoming S‐waves are increasingly being used to explore for subsurface targets. Rapid advancements in both land and marine multicomponent acquisition and processing techniques have led to numerous applications for P‐S surveys. Uses that have arisen include structural imaging (e.g., “seeing” through gas‐bearing sediments, improved fault definition, enhanced near‐surface resolution), lithologic estimation (e.g., sand versus shale content, porosity), anisotropy analysis (e.g., fracture density and orientation), subsurface fluid description, and reservoir monitoring. Further applications of P‐S data and analysis of other more complicated converted modes are developing.

High-frequency spectra observed at Anza, California: Implications for Q structure

1988 ◽  
Vol 78 (2) ◽  
pp. 692-707
Author(s):  
S. E. Hough ◽  
J. G. Anderson
Keyword(s):  
High Frequency ◽  
P Waves ◽  
Frequency Spectra ◽  
S Waves ◽  
Intrinsic Attenuation ◽  
Depth Dependence ◽  
Wide Range ◽  
Distance Dependence ◽  
Attenuation Mechanism ◽  
Inversion Procedure

Abstract Data from the Anza array in southern California have been analyzed to yield a model for the depth dependence of attenuation. The result is obtained from a formal inversion of the distance dependence of the spectral decay parameter, κ, observed from sources at a wide range of distances from single stations. The inversion procedure assumes constant Qi in plane layers and finds models which are as nearly constant with depth as possible. We find that the data cannot be explained by a model in which Qi is constant with depth and that the data generally require three-layer models. The resulting models typically give Qi for P waves between 300 and 1000 in the top 5 km, rising to 1000 to 3000 at greater depths, and decreasing to 700 to 1000 around 12 km depth. Qi for S waves is slightly higher in most cases. Because this depth dependence of Qi is generally correlated with the depths of earthquake epicenters, we suggest that Qi may be due to a pressure and temperature-controlled intrinsic attenuation mechanism.

4. Seismic waves

2018 ◽  
pp. 53-61
Author(s):  
Mike Goldsmith
Keyword(s):  
Seismic Wave ◽  
Rayleigh Waves ◽  
Seismic Waves ◽  
Shear Waves ◽  
Free Vibrations ◽  
Love Waves ◽  
Sound Waves ◽  
P Waves ◽  
Tectonic Plates ◽  
S Waves

Sound waves travel very easily underground, often for many thousands of kilometres. These are usually referred to as a kind of seismic wave and are most often triggered by earthquakes, which result from a sudden slip of tectonic plates, down to about 700 kilometres below the Earth’s surface. ‘Seismic waves’ describes the four types of seismic wave generated by earthquakes: P-waves (primary waves), S-waves (shear waves), Love waves (usually the most powerful and destructive of seismic waves), and Rayleigh waves, which are created when P and S waves reach the Earth’s surface together, combining to form undulating ground rolls. Free vibrations and star waves are also described.

Nonlinear Rheology at Shallow Depths with Reference to the 2016 Kumamoto Earthquakes

2019 ◽  
Vol 109 (6) ◽  
pp. 2674-2690 ◽  
Author(s):  
Norman H. Sleep ◽  
Nori Nakata
Keyword(s):  
Seismic Waves ◽  
Inelastic Strain ◽  
P Wave ◽  
Seismic Velocities ◽  
P Waves ◽  
S Waves ◽  
Shallow Subsurface ◽  
Horizontal Acceleration ◽  
Normal Traction ◽  
Uppermost Layer

Abstract Strong S waves produce dynamic stresses, which bring the shallow subsurface into nonlinear inelastic failure. We examine implications of nonlinear viscous flow, which may be appropriate for shallow muddy soil, and contrast them with those of Coulomb friction within a shallow reverberating uppermost layer with low‐seismic velocities. Waves refract into essentially vertical paths at the shallow layers and produce tractions on horizontal planes. The Coulomb ratio of shear traction to lithostatic stress for S waves equals the resolved horizontal acceleration normalized to the acceleration of gravity. The ratio of dynamic vertical normal traction to lithostatic stresses is the vertical normalized acceleration from P waves. The predicted viscous inelastic strain rate in muddy soil begins at low normalized accelerations and then increases mildly and nonlinearly with increasing normalized acceleration. Failure is unaffected when P waves decrease the vertical normal traction. Seismic waves recorded at KiK‐net station KMMH16 for the 2016 Kumamoto mainshock and strong foreshock show these effects. Inelastic deformation commences at a normalized horizontal acceleration of ∼0.25 and reduces S‐ and P‐wave velocities within the uppermost ∼15  m reverberating layer. Normalized horizontal accelerations and the Coulomb stress ratio reach ∼1.25. Strong S waves arrived even when strong P waves produced vertical tension on horizontal planes. In contrast, inelastic Coulomb failure commences at a normalized horizontal acceleration equal to the effective coefficient of friction; rapid inelastic strain precludes even higher accelerations. Furthermore, horizontal planes should fail from the stresses of strong S waves during the tensional cycle of strong P waves.

Corner frequencies of P and S waves and models of earthquake sources

1973 ◽  
Vol 63 (6-1) ◽  
pp. 2091-2104 ◽  
Author(s):  
Peter Molnar ◽  
Brian E. Tucker ◽  
James N. Brune
Keyword(s):  
Seismic Waves ◽  
Wave Spectra ◽  
S Wave ◽  
P Waves ◽  
S Waves ◽  
Earthquake Sources ◽  
Dislocation Models ◽  
San Fernando

Abstract P- and S-wave spectra of 144 aftershocks 12≦M≦412 of the February 9, 1971 San Fernando earthquake corroborate previous work showing that the corner frequencies for P waves in general are greater than those for S waves. This observation is consistent not only with models that treat earthquakes as volume sources, but also with physically reasonable dislocation models for which (1) the source is approximately equidimensional, (2) both the duration of slip at each point on the fault and the time for the ruptured area to develop are not long compared with the time for seismic waves to cross the ruptured area, and (3) much of the source radiates essentially simultaneously. There may be other physically reasonable dislocation models compatible with the observations. Savage's calculations indicate that models that involve propagating dislocations on long thin faults are not adequate for describing most moderate and small earthquakes studied.

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