Pore fluids and seismic attenuation in rocks

Winkler, Kenneth W.; Nur, Amos

doi:10.1029/gl006i001p00001

Cited by 344 publications

(182 citation statements)

References 22 publications

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“…The results are shown in Figure 9. It can be seen that P-waves tend to attenuate more than SH-waves, consistent with the theoretical prediction based on the conceptual model of Winkler and Nur (1979) for partially saturated rocks. The opposite behavior observed in the samples (WUK2 at 45°and WUK47B at 90°) can be related in the same way as mentioned above to more intrinsic attenuation caused by the presence of more cracks and fractures in the sample.…”

Section: Samplesupporting

confidence: 76%

Ultrasonic velocity and attenuation anisotropy of shales, Whitby, United Kingdom

et al. 2016

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We have conducted ultrasonic experiments, between 0.3 and 1 MHz, to measure velocity and attenuation (Q −1 ) anisotropy of P-and S-waves in dry Whitby Mudstone samples as a function of stress. We found the degree of anisotropy to be as large as 70% for velocity and attenuation. The sensitivity of P-wave anisotropy change with applied stress is more conspicuous than for S-waves. The closure of large aspect-ratio pores (and/or micro cracks) seems to be a dominant mechanism controlling the change of anisotropy. Generally, the highest attenuation is perceived for samples that have their bed layering perpendicular (90°) to the wave path. The observed attenuation in the samples is partly due to the scattering on the different layers, and it is partly due to the intrinsic attenuation. Changes in attenuation due to crack closure during the loading stage of the experiment are an indication of the intrinsic attenuation. The remaining attenuation can then be attributed to the layer scattering. Finally, the changes in attenuation anisotropy with applied stress are more dynamic with respect to changes in velocity anisotropy, supporting the validity of a higher sensitivity of attenuation to rock property changes.

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Section: Samplesupporting

confidence: 76%

Ultrasonic velocity and attenuation anisotropy of shales, Whitby, United Kingdom

et al. 2016

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“…HASEMI et al (1984) attributed the velocity variation to variation in temperature and degree of partial melting. The obtained attenuation structure strongly supports their interpretation because the attenuation reflects the variation of temperature and degree of fluid saturation more sensitively than the velocity does (e.g., JACKSON and ANDERSON, 1970;WINKLER and NUR, 1979). The low-Q zones in layer 2 are intersected by a relatively high-Q zone elongating in the NE-SW direction where volcanoes are distributed sparsely.…”

Section: Attenuation Structuresupporting

confidence: 54%

Determination of seismic attenuation structure and source strength by inversion of seismic intensity data: Tohoku district, northeastern Japan arc.

Hashida

Shimazaki

1987

J,Phys,Earth

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As the first application of the method of Hashida and Shimazaki (J. Phys. Earth, 32, 299-316, 1984), a three-dimensional seismic attenuation structure and source strengths are estimated by inversion of seismic intensity data for earthquakes that occurred in the Tohoku district, Japan. We carefully selected 1,630 intensity data from 101 earthquakes so that the intensities are consistent with accelerations converted from Kawasumi's relation and so that a well-resolved attenuation structure is obtained. A reasonable fit of the formula proposed in our preceding paper to the actual intensity data guarantees that a systematically biased attenuation structure is not obtained. A comparison of the obtained attenuation structure with velocity structures estimated by previous studies shows that high (low) Q nearly corresponds to high (low) V. The correlation of both structures indicates that the attenuation structure estimated by the proposed method is reliable. The resultant attenuation structure shows a remarkable contrast in the attenuation coefficient and two prominent features. The first feature is low-Q zones down to a depth of 90 km, which corresponds to the distribution of volcanoes. The second is high-Q zones that correspond to the subducting Pacific slab. The high-Q slab is in contact with the high-Q zone in a depth range of 30-60 km, which lies on the east side of the volcanic front. The presence of high-stress earthquakes in this depth range, such as the 1978 Miyagi-ken-oki earthquake, is explained by a model in which the contact of the underthrusting Pacific plate with the surface high-Q zone accumulates higher stress and thus causes stronger seismic coupling. The estimated source strength, which is expressed as a point source acceleration, correlates well with earthquake magnitude. Normalized source acceleration, which is an average acceleration over a source area, is estimated. The acceleration suggests that the stress drop of an earthquake becomes higher with magnitude and with depth. The relation between JMA magnitude (MJ) and seismic intensity at a hypocentral * Now at Seismological and Volcanological Department , Japan Meteorological Agency, Tokyo, Japan. T. HASHIDA and K. SHIMAZAKI distance of 100 km (I100) is found to be I100=1.5 MJ-6.5 for crustal events. This I100 is in agreement with the value reported by Utsu (Bull. Earthq. Res. Inst., 59, 219-233, 1984) which was determined from events excluding those which show anomalous distributions of intensity data. This agreement suggests that our method of estimating earthquake magnitude from intensity data is effective for removing the effect of structure.

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“…This optimum degree of saturation has been found to increase with a decrease in the grain size of granular material (Cho and Santamarina 2001). It has been noted that the damping ratio decreases continuously with an increase in the confining pressure for sandstone rock (Winkler and Nur 1979). Winkler and Nur (1979) observed that the value of the damping ratio becomes (1) minimum for dry rock, (2) a little higher for partially saturated rock, and (3) maximum for fully saturated rock.…”

mentioning

confidence: 72%

Damping of Sands for Varying Saturation

Madhusudhan¹,

Kumar

2013

J. Geotech. Geoenviron. Eng.

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A series of resonant column tests have been performed in the torsional mode of vibration to assess the effect of saturation, starting from the near dry state to the fully saturated state, on the damping ratio of sands corresponding to the threshold strain level. Tests were carried out on three different gradations of sand for various combinations of relative density and effective confining pressure. For fine sands, a certain optimum degree of saturation exists at which the damping ratio minimizes; it is known that a decrease in S r from a fully saturated state leads to a continuous increase in the matric suction. With an increase in the relative density, the optimum degree of saturation for fine sand increases marginally from 1.38 to 1.49%, but does not show any dependency on the effective confining pressure. In contrast, the minimum values of the damping ratio for medium and coarse sands are found to always correspond to the near dry state. The damping ratio decreases continuously with increases in relative density and effective confining pressure. The threshold strain level has been found to decrease continuously with increases in relative density and effective confining pressure.

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Pore fluids and seismic attenuation in rocks

Cited by 344 publications

References 22 publications

Ultrasonic velocity and attenuation anisotropy of shales, Whitby, United Kingdom

Ultrasonic velocity and attenuation anisotropy of shales, Whitby, United Kingdom

Determination of seismic attenuation structure and source strength by inversion of seismic intensity data: Tohoku district, northeastern Japan arc.

Damping of Sands for Varying Saturation

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