The effect of cracks on the seismic velocities of basalt from Site 990, Southeast Greenland margin

Cerney, Brian; Carlson, R. L.

doi:10.2973/odp.proc.sr.163.106.1999

Cited by 6 publications

(9 citation statements)

References 25 publications

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“…[41] The estimated aspect ratio spectra c(a m ) ( Figure 7a) were then normalized by dividing them by total porosity f 0 (equation (12)) to obtain the normalized aspect ratio spectra (Figure 7b) [Cerney and Carlson, 1999;Tsuji and Iturrino, 2008]:…”

Section: Aspect Ratio Spectrummentioning

confidence: 99%

Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan

Tsuji¹,

Tokuyama²,

Pisani³

et al. 2008

J. Geophys. Res.

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[1] We developed a theoretical method for predicting effective stress and pore pressure based on rock physics model. We applied the method to reveal the pore pressure distribution within the Nankai accretionary prism off southwestern Japan and to investigate variations in pore pressure associated with evolution of the plate boundary décollement. From the crack aspect ratio spectrum estimated from laboratory and well-log data, we calculated a theoretical relationship between acoustic velocity and mean effective stress by using differential effective medium theory. By iteratively fitting the theoretically calculated velocity to the seismic velocities derived from 3D tomographic inversion, we estimated in situ mean effective stress within the accretionary prism. Pore pressure is then the difference between the effective stress and the confining stress. When we calculated pore pressure, we considered compressive state of stress in the accretionary prism. Our results confirm that pore fluid pressure is high within the subducting sedimentary sequence below the décollement; we determined a normalized pore pressure ratio (l*) of 0.4-0.7. Abnormal pore pressures develop in the underthrust sequence as a result of the increase in overburden load because of the thickened overlying prism and a low permeability barrier across the décollement. Overpressuring within the accreted sequence is initiated at the deformation front and proceeds landward. The increase in horizontal compaction within the accreted sequence may raise pore pressures within the accreted sequence, and the pore pressure (mean effective stress) contrast at the décollement becomes smaller landward of the deformation front.Citation: Tsuji, T., H. Tokuyama, P. Costa Pisani, and G. Moore (2008), Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan,

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Section: Aspect Ratio Spectrummentioning

confidence: 99%

Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan

Tsuji¹,

Tokuyama²,

Pisani³

et al. 2008

J. Geophys. Res.

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“…() demonstrated an exponential decrease in V p over the range from 2 to 6.5 km/s as a function of porosity for basalt cores from Saudi Arabia (at zero confining pressure). Cerney and Carlson () measured a range in V p for basalt cores IDP Hole 990A on the southeast Greenland margin during Ocean Drilling Program Leg 163, from 2.2 to 6.5 km/s, reflecting differences in down‐hole rock properties, mainly mineralogy and porosity (~2–7% porosity). Third, we measured 1D P‐wave profiles on a historic flow with pahoehoe textures in order to evaluate the initial V p velocity of the Pololu volcanics just following crystallization and prior to any further weathering at the Earth's surface.…”

Section: Seismic Characterization Of the Czmentioning

confidence: 99%

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation

Voigtlander

Clark

Zekkos

et al. 2018

Earth Surf Processes Landf

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The evolution of volcanic landscapes and their landslide potential are both dependent upon the weathering of layered volcanic rock sequences. We characterize critical zone structure using shallow seismic Vp and Vs profiles and vertical exposures of rock across a basaltic climosequence on Kohala peninsula, Hawai’i, and exploit the dramatic gradient in mean annual precipitation (MAP) across the peninsula as a proxy for weathering intensity. Seismic velocity increases rapidly with depth and the velocity–depth gradient is uniform across three sites with 500–600 mm/yr MAP, where the transition to unaltered bedrock occurs at a depth of 4 to 10 m. In contrast, velocity increases with depth less rapidly at wetter sites, but this gradient remains constant across increasing MAP from 1000 to 3000 mm/yr and the transition to unaltered bedrock is near the maximum depth of investigation (15–25 m). In detail, the profiles of seismic velocity and of weathering at wet sites are nowhere monotonic functions of depth. The uniform average velocity gradient and the greater depths of low velocities may be explained by the averaging of velocities over intercalated highly weathered sites with less weathered layers at sites where MAP > 1000 mm/yr. Hence, the main effect of climate is not the progressive deepening of a near‐surface altered layer, but rather the rapid weathering of high permeability zones within rock subjected to precipitation greater than ~1000 mm/yr. Although weathering suggests mechanical weakening, the nearly horizontal orientation of alternating weathered and unweathered horizons with respect to topography also plays a role in the slope stability of these heterogeneous rock masses. We speculate that where steep, rapidly evolving hillslopes exist, the sub‐horizontal orientation of weak/strong horizons allows such sites to remain nearly as strong as their less weathered counterparts at drier sites, as is exemplified by the 50°–60° slopes maintained in the amphitheater canyons on the northwest flank of the island. Copyright © 2017 John Wiley & Sons, Ltd.

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“…Cerney and Carlson (1999) conducted two steps for determining the aspect ratios using basalt: by selecting 14 values for the aspect ratio for the first model and 7 values for the aspect ratio for the final model. Cerney and Carlson (1999) conducted two steps for determining the aspect ratios using basalt: by selecting 14 values for the aspect ratio for the first model and 7 values for the aspect ratio for the final model.…”

Section: Aspect Ratio Distributionmentioning

confidence: 99%

“…Based on this function, Tran, Rai and Sondergeld (2008) modified the spectrum using 14 values of aspect ratios for Berea sandstone. Cerney and Carlson (1999) conducted two steps for determining the aspect ratios using basalt: by selecting 14 values for the aspect ratio for the first model and 7 values for the aspect ratio for the final model.…”

Section: Aspect Ratio Distributionmentioning

confidence: 99%

“…Calculation of pore volume concentrations using the inversion method (Cheng and Toksöz 1979) has been utilized by many researchers such as Cerney and Carlson (1999), Tsuji and Iturrino (2008), Wilkens, Fryer and Karsten (1991), Tao, King and Bidhendi (1995), Tran, Rai and Sondergeld (2008), as well as many others. However, their inversion technique has several drawbacks.…”

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Elastic moduli and the aspect ratio spectrum of rock using simulated annealing

Izumotani¹,

Onozuka²

2013

Geophysical Prospecting

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We propose a new method for estimating pore volume concentrations associated with inclusions with different aspect ratios and also the rock matrix and pore fluid moduli using very fast simulated annealing. We use the Kuster and Toksöz effective modulus formulations as a forward model that takes the pore shapes into consideration. In order to provide this method, we first estimated the model parameters, then calculated the P‐ and S‐wave velocities as a function of pressure in dry and saturated conditions and finally compared the calculated velocities with the measured ultrasonic velocities of sandstone, limestone and granite. The calculated velocity fitted well with the measured velocity. Furthermore, we verified the calculated bulk modulus and shear modulus of the rock matrix. As these moduli were consistent with the results from other experiments and were almost the same as those by the inversion method, we believe that this method can satisfactorily calculate the moduli. Next, we conducted optimization under several cases of moduli setting. We obtained the best results using the independent shear modulus under saturated conditions. The result indicates that the shear modulus varies according to the fluid in the pores in sandstone. Finally, we optimized the average aspect ratio of rock and found that the average aspect ratio may depend on the type of rock. The velocity calculated by the single aspect ratio is similar to the velocity calculated by using a spectrum of aspect ratios for the same rock.

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The effect of cracks on the seismic velocities of basalt from Site 990, Southeast Greenland margin

Cited by 6 publications

References 25 publications

Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan

Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation

Elastic moduli and the aspect ratio spectrum of rock using simulated annealing

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