On the generation of tangential ground motion by underground explosions in jointed rocks

Vorobiev, O.; Ezzedine, S. M.; Antoun, T.; Glenn, L. A.

doi:10.1093/gji/ggu478

Cited by 19 publications

(12 citation statements)

References 33 publications

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“…The maximum motion is observed in the direction of the maximum shear stress (at 45 ∘ to the principal stress directions). As it was shown in Vorobiev et al (2015Vorobiev et al ( , 2017, joint-driven mechanism very often produces maximum tangential velocity and displacement magnitudes during the second phase of the pulse when polarity of the motion changes because initial shock wave compression is followed by a unloading wave. Because the joint strength is smaller during unloading, more joints start to slide, and since the radial velocity changes sign, so does the tangential.…”

Section: Distinguishing Between Two Mechanisms Of Shear Wave Generationmentioning

confidence: 87%

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Two Sources of Nonisotropic Radiation From Underground Explosions in Granite

Vorobiev

2017

JGR Solid Earth

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Significant tangential ground motion observed during underground explosions makes it difficult to distinguish them from natural earthquakes. Such motion can be generated by the source geometry and emplacement conditions, by the heterogeneous nature of the rock mass (mechanical properties may vary in space due to the presence of cracks, joints, faults, and various geologic layers) and also by the nonuniform in situ stress state. The last mechanism is increasingly important with depth when the difference in main principal stresses becomes significant. This paper is focused on the role of material strength of the rock mass in generation of nonradial motion during explosions in prestressed media. Numerical modeling of underground chemical explosions in granite at various depths has been conducted to compare two possible mechanisms of shear wave generation. The first, caused by rock mass anisotropy, is important at shallow depth. The second is related to elastic‐plastic relaxation around the cavity created by the explosion. Tangential motions for these two mechanisms have different signatures.

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Section: Distinguishing Between Two Mechanisms Of Shear Wave Generationmentioning

confidence: 87%

“…The joints have properties distinct from the material properties. Detailed description of the constitutive laws used for the joints is given in Hurley et al (2017) and Vorobiev et al (2015).…”

Section: Modeling Assumptionsmentioning

confidence: 99%

Two Sources of Nonisotropic Radiation From Underground Explosions in Granite

Vorobiev

2017

JGR Solid Earth

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“…This paper focussed on the anisotropic influence of multiple joint sets on the response of rock by specifying the rock medium to be isotropic, which is a reasonable assumption in the near field . Future work is planned to generalize the model to include general elastic anisotropy to be able to more accurately capture anisotropic elastic wave propagation far from the explosive source.…”

Section: Discussionmentioning

confidence: 99%

“…A number of models have been developed for jointed rocks (eg, Sayers and Kachanov and Tsvankin and Grechka, but most of them are limited to elastic seismic wave propagation. These elastic models cannot simulate the nonlinearity controlling anisotropic joint slippage observed in mesoscale simulations near the source of the explosion (eg, Vorobiev et al and Vorobiev.…”

Section: Introductionmentioning

confidence: 99%

A thermomechanical anisotropic continuum model for geological materials with multiple joint sets

Vorobiev

Rubin

2018

Num Anal Meth Geomechanics

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Summary Joints in geological materials introduce elastic compliance and weak planes on which sliding can occur. Although these materials can have multiple joint sets, they often have preferred orientations that cause both elastic and inelastic anisotropic response even when the unjointed material is isotropic. Azimuthal variations in radial velocity and polarity of tangential motion have been observed in experimental data for wave propagation caused by an initially spherical source in a geological material with multiple joint sets. This observed tangential ground motion was found to be related to mechanical anisotropy caused by preferred orientations of joints in the rock. This paper describes thermomechanical continuum constitutive equations, which model the effects of multiple persistent joint sets. A number of quasi‐static examples are considered, which show that the proposed model predicts anisotropic effects of sliding on multiple joint sets similar to those exhibited by computationally expensive mesoscale calculations, which model joint sets explicitly.

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“…In the case of preexisting stress in the medium, the explosion can release tectonic elastic strain throughout the damaged zone around the cavity [ Press and Archambeau , ; Toksoz et al , ; Wallace et al , ; Stevens and Thompson , ] or by triggering a nearby earthquake [ Aki et al , ; Aki and Tsai , ], which also leads to shear waves generation. Moreover, interesting numerical experiments tend to show that sliding of discrete rock masses at joints under the effect of the stress wave could be the origin of tangential components of motion [ Heuzé et al , ; Vorobiev et al , ], which can also be compared to observations in the far‐field by using coupling techniques between hydrodynamic modeling and elastic modeling [ Pitarka et al , ].…”

Section: Introduction and Motivationsmentioning

confidence: 99%

Homogenized moment tensor and the effect of near‐field heterogeneities on nonisotropic radiation in nuclear explosion

2016

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We investigate the effect of small‐scale heterogeneities close to a seismic explosive source, at intermediate periods (20–50 s), with an emphasis on the resulting nonisotropic far‐field radiation. First, using a direct numerical approach, we show that small‐scale elastic heterogeneities located in the near‐field of an explosive source, generate unexpected phases (i.e., long period S waves). We then demonstrate that the nonperiodic homogenization theory applied to 2‐D and 3‐D elastic models, with various pattern of small‐scale heterogeneities near the source, leads to accurate waveforms at a reduced computational cost compared to direct modeling. Further, it gives an interpretation of how nearby small‐scale features interact with the source at low frequencies, through an explicit correction to the seismic moment tensor. In 2‐D simulations, we find a deviatoric contribution to the moment tensor, as high as 21% for near‐source heterogeneities showing a 25% contrast of elastic values (relative to a homogeneous background medium). In 3‐D this nonisotropic contribution reaches 27%. Second, we analyze intermediate‐periods regional seismic waveforms associated with some underground nuclear explosions conducted at the Nevada National Security Site and invert for the full moment tensor, in order to quantify the relative contribution of the isotropic and deviatoric components of the tensor. The average value of the deviatoric part is about 35%. We conclude that the interactions between an explosive source and small‐scale local heterogeneities of moderate amplitude may lead to a deviatoric contribution to the seismic moment, close to what is observed using regional data from nuclear test explosions.

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On the generation of tangential ground motion by underground explosions in jointed rocks

Cited by 19 publications

References 33 publications

Two Sources of Nonisotropic Radiation From Underground Explosions in Granite

Two Sources of Nonisotropic Radiation From Underground Explosions in Granite

A thermomechanical anisotropic continuum model for geological materials with multiple joint sets

Homogenized moment tensor and the effect of near‐field heterogeneities on nonisotropic radiation in nuclear explosion

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