Frequency dependent characteristics of coda wave quality factor in central and southcentral Alaska

1988 ◽  
Vol 128 (1-2) ◽  
pp. 295-307 ◽  
Author(s):  
G. J. Steensma ◽  
N. N. Biswas
Keyword(s):  
Quality Factor ◽  
Coda Wave ◽  
Frequency Dependent ◽  
Southcentral Alaska

Attenuation and dispersion of P-waves in fluid-saturated porous rocks with a distribution of coplanar cracks - scattering approach

Geophysics ◽  
2020 ◽  
pp. 1-54
Author(s):  
Yongjia Song ◽  
Jun Wang ◽  
Hengshan Hu ◽  
Bo Han
Keyword(s):  
Quality Factor ◽  
Scattering Problem ◽  
Crack Density ◽  
Relaxation Frequency ◽  
P Wave ◽  
Frequency Dependent ◽  
Low Frequencies ◽  
Attenuation And Dispersion ◽  
Dispersion And Attenuation ◽  
Coplanar Cracks

Wave-induced fluid flow (WIFF) between cracks and micro-pores is one of the major mechanisms in causing attenuation and dispersion within seismic frequency ranges. Previous non-interaction-approximation (NIA) models often assume the distribution of cracks is dilute, neglecting the influences of interacting cracks on dispersion and attenuation. To overcome this restriction, we investigate the interaction between coplanar cracks and their influences on seismic dispersion and attenuation. First, a scattering problem for a longitudinal (P) wave normally impinging on a plane with equally distributed coplanar cracks in a porous medium is solved using integral transform approach. Then, based on the solution, an effective wavenumber is derived for P-wave propagation in a porous material with coplanar cracks. It is found that the magnitude of dispersion and attenuation can significantly increase when the spacing between adjacent cracks decreases even if the crack density is unchanged. Moreover, frequency-dependent asymptotic behavior of inverse quality factor is also different from that of the NIA models at frequencies lower than the WIFF relaxation frequency. Specifically, the inverse quality factor scales with the square root of frequency at low frequencies. When the spacing between adjacent cracks is large, an additional frequency-dependent scale occurs at relatively higher frequencies (but still lower than the WIFF relaxation frequency) with inverse quality factor scales with the first power of frequency. When the spacing becomes much larger so that the interaction between the adjacent cracks is negligible, the present model exactly reduces to a NIA model for a distribution of aligned slit cracks and the first power scale can prevail attenuation within low frequencies.

Determination of high-frequency attenuation characteristic of coda waves in the central region of Nepal Himalaya

2020 ◽  
Vol 60 ◽  
pp. 75-86
Author(s):  
Thakur Prasad Kandel ◽  
Masumi Yamada ◽  
Prakash Pokhrel
Keyword(s):  
Quality Factor ◽  
Central Region ◽  
High Frequency ◽  
Wave Attenuation ◽  
Tectonic Setting ◽  
Coda Wave ◽  
Window Length ◽  
Seismic Stations ◽  
High Attenuation ◽  
Coda Wave Attenuation

The high-frequency coda wave attenuation in the central region of Nepal, in and around the Kathmandu valley, is estimated using vertical component seismograms of local earthquakes recorded at 16 different seismic stations of NAMASTE array. The estimated result is expressed in terms of Qc, quality factor (inverse of coda wave attenuation). The value of coda quality factor (Qc) is estimated at eight central frequencies of 1.5, 3.0, 6.0, 9.0, 12.0, 15.0, 18.0, and 21.0 Hz through four different coda window length from 20 to 50 s at 10 s interval by using the single backscattering model. The value of coda Qc obtained from this study, shows a clear dependence on a frequency according to the power relation, Qc (f)= Q0 f n, where Q0  is Qc  at 1 Hz, and f is frequency and n represents the degree of frequency dependence. The mean value of Qc of 16 different seismic stations was obtained as (110 ± 10.6) f 1.03±0.03 at 30 s coda window length, which represents the high attenuation characteristics of the study area, and attenuation decreases with increasing central frequency. Qo increases from 73.1 ± 10.1 to 156.1 ± 13.6 and n decreases from 1.12 ± 1.05 to 0.92±0.03 when the coda window length increases from 20 to 50 s. It is concluded that the study area is tectonically very active, highly heterogeneous, and heterogeneity decrease with depth. The coda Q obtained in this study is compatible with the result obtained in the region having a similar tectonic setting.

Laboratory evidence for Krauklis-wave resonance in fractures and implications for seismic coda wave analysis

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. T285-T293 ◽  
Author(s):  
Pei-Ju Rita Shih ◽  
Marcel Frehner
Keyword(s):  
Analytical Solution ◽  
Resonance Frequency ◽  
Quality Factor ◽  
Laboratory Data ◽  
Rock Properties ◽  
Coda Wave ◽  
Resonance Effects ◽  
Seismic Coda ◽  
Major Interest ◽  
Over Time

Krauklis waves are of major interest because they can lead to resonance effects in fluid-filled fractures. This resonance is marked by seismic signals with a dominant signature frequency, which may reveal fracture-related rock properties. In our laboratory study, we used homogeneous Plexiglas samples containing a single well-defined (i.e., manufactured) fracture. We recorded the signals obtained from propagating ultrasonic P- and S-waves (source frequency: 0.6, 1, and 2.25 MHz) along a sample without a fracture and samples with a fracture with different inclination angles of 30°, 45°, and 60° with respect to the short axis. The experimental results obtained from an incident S-wave confirmed that the presence of the fracture led to resonance effects at frequencies lower than the dominant source frequency, which slowly decayed over time in the recorded seismic coda after the first arrival. The resonance frequency was independent of the fracture orientation and the source frequency. We have interpreted this narrow-banded coda signal as a resonance in the fracture, and the frequency at which this occurred was an intrinsic property of the fracture size and elastic properties. To verify our laboratory results, we used an analytical solution, which provided a relationship between the fracture width, fracture length, resonance frequency, and temporal quality factor (i.e., exponential decay over time). The temporal quality factor obtained from our laboratory data agreed very well with the analytical solution. Hence, we concluded that the observed signature frequency (approximately 0.1 MHz) in the seismic coda was indeed a resonance effect. Finally, we have developed possible applications on the reservoir scale to infer fracture-related properties based on seismic coda analysis.

Frequency‐dependent Q‐estimation of Love‐type channel waves and the application of Q‐correction to seismograms

Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1773-1789 ◽  
Author(s):  
Xiao‐Ping Li ◽  
Wolfgang Schott ◽  
Horst Rüter
Keyword(s):  
Dispersion Relation ◽  
Coal Seam ◽  
Quality Factor ◽  
Wave Energy ◽  
Nonlinear Function ◽  
Ratio Method ◽  
Elastic Model ◽  
Quality Factors ◽  
Frequency Dependent ◽  
Channel Wave

We present the absorption dispersion relation of Love‐type channel waves for a simple, symmetric, homogenous, three‐layered, linear elastic model assuming that the quality factors of coal [Formula: see text] and country rock [Formula: see text] are constant. We introduce complex propagation functions into the known dispersion relation describing most of the properties of the Love‐ type channel waves. The complex dispersion relation is expanded into power series of [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text] factor of the Love‐type channel wave). The real part of the ensuing dispersion relation gives the usual dispersion relation. The imaginary part yields the frequency relation between the quality factor of Love‐type channel waves and the constant quality factors of coal and rock. In this case, [Formula: see text] depends on the frequency because the phase velocity is a function of frequency. Therefore, the attenuation coefficient is a nonlinear function of frequency. The analysis of the analytical result shows that at high frequencies the Love‐type channel wave energy is completely propagating inside the coal seam, and hence its propagation is determined by the physical properties of the coal alone. As the frequency approaches zero, the Love‐type channel wave energy is completely propagating in the rock, since the thickness of the coal is small compared to the wavelength of the channel wave, and hence the channel wave does not “see” the coal seam. The spectral ratio method is used to estimate the frequency‐dependent quality factor [Formula: see text] of Love‐type channel waves. This technique is demonstrated by applying it first to synthetic data and then to data of a well‐designed transmission survey. Finally, we use the estimated [Formula: see text] to derive an inverse Q‐operator and apply it for Q‐correction to both data sets.

Seismic attenuation tomography using body-wave energy normalised by the heterogeneous coda

2020 ◽  
Author(s):  
Panayiota Sketsiou ◽  
Luca De Siena ◽  
Simona Gabrielli ◽  
Ferdinando Napolitano
Keyword(s):  
Quality Factor ◽  
Wave Energy ◽  
Body Wave ◽  
Seismic Attenuation ◽  
Coda Wave ◽  
Total Quality ◽  
Lapse Time ◽  
Density Spectrum ◽  
Coda Normalization ◽  
Coda Attenuation

<p>Seismic waves lose energy during propagation in heterogeneous Earth media. Their decrease of amplitude, defined as seismic attenuation, is central in the description of seismic wave propagation. The attenuation of coherent waves can be described by the total quality factor, <em>Q</em>, and it is defined as the fractional energy lost per cycle, controlling the decay of the energy density spectrum with lapse time. The coda normalization (CN) method is a method to measure the attenuation of P- or S-waves by taking the ratio of the direct wave energy and late coda wave energy in order to remove the source and site effects from P- and S-wave spectra. One of the main assumptions of the CN method is that coda attenuation, i.e. the decay of coda energy with lapse time measured by the coda quality factor <em>Q<sub>c</sub></em> is constant. However, several studies showed that Q<sub>c</sub> is not uniform in the crust for the lapse times considered in most attenuation studies. In this work, we propose a method to overcome this assumption, measuring coda attenuation for each source-station path and evaluating the effect of different scattering regimes on the corresponding imaging. The data consists of passive waveforms from the fault network in the Pollino Area (Southern Italy) and Mount St. Helens volcano (USA).</p>

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