Dynamic and static moduli

Cheng, C.H.; Johnston, David H.

doi:10.1029/gl008i001p00039

Cited by 157 publications

(89 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…5.28, 5.29, and 5.30 show the ratio of static and dynamic Young's, bulk, and shear moduli, respectively, as functions of applied compressive stress. All these ratios presented similar trends: the higher the compressive stress, the higher the ratio, as we seen in the sandstones and granites studied by Cheng and Johnston (1981). In the first cycle, for compressive stresses lower than 30 bars during loading, the ratios were higher than for higher compressive stresses and unloading.…”

Section: Static and Dynamic Elastic Constants Comparisonsupporting

confidence: 63%

See 1 more Smart Citation

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Mavko¹

2006

View full text Add to dashboard Cite

Summary of Accomplishments and ResultsWe completed our planned work on anisotropy in loose unconsolidated sediments.An important accomplishment was to understand the seismic velocity anisotropy resulting from the combined roles of depositional stratification and stress in unconsolidated sands. This work has lead to one Ph.D. dissertation, and two conference presentations (SEG, 2003). The expanded abstracts from the conference proceedings were attached in the annual report for [2003][2004]. The completed Ph.D. dissertation is forms part of this final report as attachment A.The dissertation presents an experimental study of velocity anisotropy in unconsolidated sands at measured compressive stresses up to 40 bars, which correspond to the first hundred meters of the subsurface. Two types of velocity anisotropy are considered, that due to intrinsic textural anisotropy, and that due to stress anisotropy.Three types of tests were performed: (1) hydrostatic pressure, (2) quasihydrostatic stress, in which, cubic samples are placed in the polyaxial cell and approximately equal forces are applied in each of the three principal directions; and (3) uniaxial strain, in which, cubic samples are placed in the polyaxial cell and an axial stress is applied in the Zdirection, while the horizontal platens are held fixed, at approximately zero displacement. The hydrostatic pressure test is used to compare the standard velocity measurements with the velocity anisotropy measured in the polyaxial cell. The quasi-hydrostatic stress test is used to study the velocity anisotropy resulting from intrinsic anisotropy of the granular materials. The uniaxial strain test is used to study the velocity anisotropy resulting from stress anisotropy in sands. We found that intrinsic and stress-induced anisotropy can be detected in sands using Vp. The intrinsic velocity anisotropy was studied using P-wave velocities and the textural anisotropy was studied using the spatial autocorrelation function of sediment images for sands and glass beads. The results suggest that P-wave velocity anisotropy and textural anisotropy are related for grain segregation or stratification. We found that sand samples display a bi-linear dependence of velocity anisotropy with stress anisotropy. There exists a transition stress beyond which the stressinduced anisotropy outweighs the intrinsic anisotropy for three different sands. In addition, the dissertation discusses the problem of extrapolating acoustic velocities measured under hydrostatic pressure to quasi-hydrostatic stress. Measured Vp under hydrostatic pressure is higher than Vp measured under quasi-hydrostatic stress in the sand, for the same depositional anisotropy and similar isotropic stress. This difference might be due to boundary effects in the apparatus, and due to complexity of the stress field inside of the granular material samples. Finally, we found that the model of Norris I find that intrinsic and stress-induced anisotropy can be detected in sands using Vp. I study the intrinsic velocity anisotropy usi...

show abstract

Section: Static and Dynamic Elastic Constants Comparisonsupporting

confidence: 63%

“…For example, Cheng and Johnston (1981) showed that the ratio between the static and dynamic bulk moduli, Ks/Kd, at atmospheric pressure is lower for samples with higher crack porosity:…”

Section: Static and Dynamic Elastic Constants Comparisonmentioning

confidence: 99%

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Mavko¹

2006

View full text Add to dashboard Cite

show abstract

“…Laboratory experiments [Cheng and Johnston, 1981;Adelinet et al, 2010] show that statically determined values of Young's modulus, E s , are always less than dynamically determined values, E d , and that the E s /E d ratio increases with confining pressure, and decreases with porosity and crack density. Here, confining pressure is estimated by integrating the product of the density and the depth (Figure 6d).…”

Section: Mechanical Properties Of the Crustmentioning

confidence: 99%

“…(d) Ambient lithostatic pressure computed from the presumed density structure. (e) Ratio of static to dynamic Young's modulus from laboratory measurements [Cheng and Johnston, 1981]. (f) Estimated static value of Young's modulus.…”

Section: Mechanical Properties Of the Crustmentioning

confidence: 99%

“…[30] We further consider an elevated porosity and crack density close to the surface, leading to a lower ratio of E s /E d of 0.1 which was determined by Cheng and Johnston [1981] for tuffs at very low confining pressures. The E s /E d ratio for larger confining pressures is estimated from the study of Adelinet et al [2010].…”

Section: Mechanical Properties Of the Crustmentioning

confidence: 99%

See 1 more Smart Citation

Magma sources involved in the 2002 Nyiragongo eruption, as inferred from an InSAR analysis

Wauthier¹,

Cayol²,

Kervyn³

et al. 2012

J. Geophys. Res.

View full text Add to dashboard Cite

along a 20 km-long fracture network extending from the volcano to the city of Goma. The event was captured by InSAR data from the ERS-2 and RADARSAT-1 satellites. A combination of 3D numerical modeling and inversions is used to analyze these displacements. Using Akaike Information Criteria, we determine that a model with two subvertical dikes is the most likely explanation for the 2002 InSAR deformation signal. A first, shallow dike, 2 km high, is associated with the eruptive fissure, and a second, deeper dike, 6 km high and 40 km long, lies about 3 km below the city of Goma. As the deep dike extends laterally for 20 km beneath the gas-rich Lake Kivu, the interaction of magma and dissolved gas should be considered as a significant hazard for future eruptions. A likely scenario for the eruption is that the magma supply to a deep reservoir started ten months before the eruption, as indicated by LP events and tremor. Stress analysis indicates that the deep dike could have triggered the injection of magma from the lake and shallow reservoir into the eruptive dike. The deep dike induced the opening of the southern part of this shallow dike, to which it transmitted magma though a narrow dike. This model is consistent with the geochemical analysis, the lava rheology and the pre-and post-eruptive seismicity. We infer low overpressures (1-10 MPa) for the dikes. These values are consistent with lithostatic crustal stresses close to the dikes and low magma pressure. As a consequence, the dike direction is probably not controlled by stresses but rather by a reduced tensile strength, inherited from previous rift intrusions. The lithostatic stresses indicate that magmatic activity is intense enough to relax tensional stresses associated with the rift extension.

show abstract

Microstructural controls on the physical and mechanical properties of edifice‐forming andesites at Volcán de Colima, Mexico

et al. 2014

View full text Add to dashboard Cite

The reliable assessment of volcanic unrest must rest on an understanding of the rocks that form the edifice. It is their microstructure that dictates their physical properties and mechanical behavior and thus the response of the edifice to stress perturbations during unrest. We evaluate the interplay between microstructure and rock properties for a suite of edifice-forming rocks from Volcán de Colima (Mexico). Microstructural analyses expose (1) a pervasive, isotropic microcrack network, (2) a high, subspherical vesicle density, and (3) a wide vesicle size distribution. This complex microstructure severely impacts their physical and mechanical properties. In detail, porosities are high and range from 8 to 29%. As a consequence, elastic wave velocities, Youngs moduli, and uniaxial compressive strengths are low, and permeabilities are high. All of the rock properties demonstrate a wide range. For example, strength decreases by a factor of 8 and permeability increases by 4 orders of magnitude over the porosity range. Below a porosity of 11-14%, the permeability-porosity trend follows a power law with a much higher exponent. Microstructurally, this represents a critical vesicle content that efficiently connects the microcrack population and permits a much more direct path through the sample, rather than restricting flow to long and tortuous microcracks. Values of tortuosity inferred from the Kozeny-Carman permeability model support this hypothesis. However, we find that the complex microstructure precludes a complete description of their mechanical behavior through micromechanical modeling. We urge that the findings of this study be considered in volcanic hazard assessments at andesitic stratovolcanoes.

show abstract

Dynamic and static moduli

Cited by 157 publications

References 8 publications

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Magma sources involved in the 2002 Nyiragongo eruption, as inferred from an InSAR analysis

Microstructural controls on the physical and mechanical properties of edifice‐forming andesites at Volcán de Colima, Mexico

Contact Info

Product

Resources

About