A comparative study of coda–Q values estimations from synthetic and digital seismograms

Abstract The attenuation of shear waves in the crust is estimated, for frequencies between 1.5 and 12.0 Hz, by applying a single-station method based on the rate of decay of the S-wave to coda-wave amplitude ratio with distance. The data used come from local earthquakes that occurred in the Thessaloniki area, northern Greece, during the period 1983 through 1989 and were recorded by the telemetered network of the Geophysical Laboratory of the University of Thessaloniki. The Qs values obtained are 115, 244, 477, and 755 for 1.5, 3.0, 6.0, and 12.0 Hz, respectively. These values are very close to the coda Q values estimated for the same area using the S-to-S single scattering model for lapse times between 30 and 100 sec but they are higher than the coda Q values for lapse times between 10 and 30 sec. The estimated Qs is found to be strongly frequency dependent, proportional to f0.91, which is very close to the frequency dependence of the coda Q.

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Coda Q before the 1983 Hawaii (MS = 6.6) earthquake

Bulletin of the Seismological Society of America ◽

10.1785/bssa0780031279 ◽

1988 ◽

Vol 78 (3) ◽

pp. 1279-1296

Author(s):

Zhong-Xian Huang ◽

Max Wyss

Keyword(s):

Unit Volume ◽

Main Shock ◽

B Value ◽

Rectangular Region ◽

S Wave ◽

Coda Q ◽

Seismicity Rate ◽

High Q ◽

Source Mechanisms ◽

Q Values

Abstract Coda Q values were derived for more than 300 microearthquakes that occurred in a 6-yr period before the 16 November 1983 Kaoiki, Hawaii, earthquake (MS = 6.6). The sources were located within a 14 × 16 km rectangular region surrounding the main shock epicenter, and most of them occurred at depths between 5 and 10 km. Digital recordings from three stations at epicentral distances ranging from 0 to 18 km were used. Coda Q was calculated from the amplitude decay rate of the S-wave coda in nine frequency bands from 4.5 to 27 Hz. The average Q of the NW part of the studied area is about 15 per cent higher than that of the SE part. These two subregions also showed differences in seismicity, b value, and microearthquake source mechanisms. In the high-Q volume, the b value was 1.0, and the rate of earthquakes per unit volume was about 50 per cent of the rate in the low-Q volume where b = 1.3. One interpretation of these observations is that more extensive faulting in the SE Kaoiki fault zone leads to lower Q, higher b value, and a higher seismicity rate. During the 5 to 6 yr before the mainshock, the 1-yr average Q values were stable. No significant Q change could be identified as a precursor to the main shock.

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A comparative study of scattering, intrinsic, and coda Q−1for Hawaii, Long Valley, and central California between 1.5 and 15.0 Hz

Journal of Geophysical Research Atmospheres ◽

10.1029/91jb03094 ◽

1992 ◽

Vol 97 (B5) ◽

pp. 6643 ◽

Cited By ~ 159

Author(s):

Kevin Mayeda ◽

Stuart Koyanagi ◽

Mitsuyuki Hoshiba ◽

Keiiti Aki ◽

Yuehua Zeng

Keyword(s):

Comparative Study ◽

Coda Q ◽

Central California ◽

Long Valley

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Energy-flux model of seismic coda: Separation of scattering and intrinsic attenuation

Bulletin of the Seismological Society of America ◽

10.1785/bssa0770041223 ◽

1987 ◽

Vol 77 (4) ◽

pp. 1223-1251

Author(s):

Arthur Frankel ◽

Leif Wennerberg

Keyword(s):

Decay Rate ◽

Energy Flux ◽

Single Scattering ◽

Coda Q ◽

Scattering Attenuation ◽

Seismic Coda ◽

Wide Range ◽

Flux Model ◽

Strong Scattering ◽

Q Values

Abstract A new model of seismic coda is presented, based on the balance between the energy scattered from the direct wave and the energy in the seismic coda. This energy-flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic (anelastic) attenuation of the medium. This formula is valid for both weak and strong scattering and implicitly includes multiple scattering. The model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity. Some of the simulations also included intrinsic dissipation. The energy-flux model explains the coda decay and amplitude observed in the synthetics, for random media with a wide range of scattering Q. In contrast, the single-scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation (scattering Q ≦ 150). The simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate, as predicted by the energy-flux model. The coda decay rate is sensitive, however, to the intrinsic Q of the medium. The ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation. Thus, analysis of the decay rate and amplitude of the coda can, in principle, produce separate estimates for the scattering and intrinsic Q values of the crust. We analyze the coda from two earthquakes near Anza, California. Intrinsic Q values determined from these seismograms using the energy-flux model are comparable to coda Q values found from the single-scattering theory. These results indicate that coda Q values are, at best, measures of the intrinsic Q of the lithosphere and are unrelated to the scattering Q.

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Measurements of intrinsic and scattering seismic attenuation in the crust

Bulletin of the Seismological Society of America ◽

10.1785/bssa0850051373 ◽

1995 ◽

Vol 85 (5) ◽

pp. 1373-1380 ◽

Cited By ~ 3

Author(s):

Edoardo Del Pezzo ◽

Jesus Ibanez ◽

José Morales ◽

Aybige Akinci ◽

Rosalba Maresca

Keyword(s):

Seismic Attenuation ◽

Campi Flegrei ◽

Etna Volcano ◽

S Wave ◽

Coda Q ◽

Shallow Earthquakes ◽

Tectonically Active ◽

Intrinsic And Scattering Attenuation ◽

Q Values ◽

Degree Of Heterogeneity

Abstract Intrinsic and scattering attenuation parameters, Qi and QS, have been measured in three different tectonic areas for local and shallow earthquakes located close to the receiver. The approach developed by Wennerberg (1993), which takes into account the numerical correction of the coda-Q parameter for the multiple scattering formulation of Zeng, was used to infer from the estimates of coda Q and direct S-wave Q the intrinsic (Qi) and scattering (QS) Q values. Results for 1 to 12 Hz range show that Qi is comparable to QS for the Etna volcano and for the Campi Flegrei area, while Qi for the tectonically active area of Granada is lower than QS. Coda Q is close to intrinsic Q, suggesting that, at least in the crust, coda Q is a good estimate of the intrinsic Q. Volcanic areas show a reasonable higher degree of heterogeneity, if compared with the nonvolcanic area of Granada.

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