Dilatancy and Fracture Induced Velocity Changes in Rock and their Relation to Frictional Sliding

1978 ◽  
pp. 743-764
Author(s):  
F. Rummel ◽  
H. J. Alheid ◽  
C. Frohn
Keyword(s):  
Frictional Sliding ◽  
Velocity Changes ◽  
Induced Velocity

Dilatancy and fracture induced velocity changes in rock and their relation to frictional sliding

1978 ◽  
Vol 116 (4-5) ◽  
pp. 743-764 ◽  
Author(s):  
F. Rummel ◽  
H. J. Alheid ◽  
C. Frohn
Keyword(s):  
Frictional Sliding ◽  
Velocity Changes ◽  
Induced Velocity

scholarly journals Pressure effects on water vapour lines: beyond the Voigt profile

2012 ◽  
Vol 370 (1968) ◽  
pp. 2495-2508 ◽  
Author(s):  
N. H. Ngo ◽  
H. Tran ◽  
R. R. Gamache ◽  
J. M. Hartmann
Keyword(s):  
Water Vapour ◽  
Line Shape ◽  
Pressure Effects ◽  
Shape Model ◽  
Line Shapes ◽  
Voigt Profile ◽  
Voigt Model ◽  
Velocity Changes ◽  
Dynamics Simulations ◽  
Induced Velocity

A short overview of recent results on the effects of pressure (collisions) regarding the shape of isolated infrared lines of water vapour is presented. The first part of this study considers the basic collisional quantities, which are the pressure-broadening and -shifting coefficients, central parameters of the Lorentzian (and Voigt) profile and thus of any sophisticated line-shape model. Through comparisons of measured values with semi-classical calculations, the influences of the molecular states (both rotational and vibrational) involved and of the temperature are analysed. This shows the relatively unusual behaviour of H 2 O broadening, with evidence of a significant vibrational dependence and the fact that the broadening coefficient (in cm −1 atm −1 ) of some lines increases with temperature. In the second part of this study, line shapes beyond the Voigt model are considered, thus now taking ‘velocity effects’ into account. These include both the influence of collisionally induced velocity changes that lead to the so-called Dicke narrowing and the influence of the dependence of collisional parameters on the speed of the radiating molecule. Experimental evidence of deviations from the Voigt shape is presented and analysed. The interest of classical molecular dynamics simulations, to model velocity changes, together with semi-classical calculations of the speed-dependent collisional parameters for line-shape predictions from ‘first principles’, are discussed.

Hydraulic Injection‐Induced Velocity Changes Revealed by Surface Wave Coda and Polarization Data at a Shale Play Site in Southwest China

2020 ◽  
Vol 125 (10) ◽  
Author(s):  
Yan Zhang ◽  
Fenglin Niu ◽  
Kai Tao ◽  
Jieyuan Ning ◽  
Haichao Chen ◽  
...  
Keyword(s):  
Surface Wave ◽  
Southwest China ◽  
Polarization Data ◽  
Velocity Changes ◽  
Induced Velocity

Theory of traveltime shifts around compacting reservoirs: 3D solutions for heterogeneous anisotropic media

Geophysics ◽  
2009 ◽  
Vol 74 (1) ◽  
pp. D25-D36 ◽  
Author(s):  
Rodrigo Felício Fuck ◽  
Andrey Bakulin ◽  
Ilya Tsvankin
Keyword(s):  
Isotropic Medium ◽  
Transversely Isotropic ◽  
Anisotropic Media ◽  
Time Lapse ◽  
Theory Of Elasticity ◽  
Closed Form Expression ◽  
Reservoir Compaction ◽  
Velocity Changes ◽  
Zero Offset ◽  
Induced Velocity

Time-lapse traveltime shifts of reflection events recorded above hydrocarbon reservoirs can be used to monitor production-related compaction and pore-pressure changes. Existing methodology, however, is limited to zero-offset rays and cannot be applied to traveltime shifts measured on prestack seismic data. We give an analytic 3D description of stress-related traveltime shifts for rays propagating along arbitrary trajectories in heterogeneous anisotropic media. The nonlinear theory of elasticity helps to express the velocity changes in and around the reservoir through the excess stresses associated with reservoir compaction. Because this stress-induced velocity field is both heterogeneous and anisotropic, it should be studied using prestack traveltimes or amplitudes. Then we obtain the traveltime shifts by first-order perturbation of traveltimes that accounts not only for the velocity changes but also for 3D deformation of reflectors. The resulting closed-form expression can be used efficiently for numerical modeling of traveltime shifts and, ultimately, for reconstructing the stress distribution around compacting reservoirs. The analytic results are applied to a 2D model of a compacting rectangular reservoir embedded in an initially homogeneous and isotropic medium. The computed velocity changes around the reservoir are caused primarily by deviatoric stresses and produce a transversely isotropic medium with a variable orientation of the symmetry axis and substantial values of the Thomsen parameters [Formula: see text] and [Formula: see text]. The offset dependence of the traveltime shifts should play a crucial role in estimating the anisotropy parameters and compaction-related deviatoric stress components.

An innovative method to simulate stress-induced velocity changes in anisotropic rock

2021 ◽  
Vol 11 (4) ◽  
pp. 1-18
Author(s):  
Q. Bai ◽  
H. Konietzky
Keyword(s):  
Seismic Velocity ◽  
Numerical Models ◽  
Crack Density ◽  
Bedding Plane ◽  
Anisotropic Rock ◽  
Proposed Model ◽  
Isotropic Structure ◽  
Velocity Changes ◽  
Induced Velocity ◽  
Stress Dependent

This contribution proposes a numerical microstructural modeling approach to investigate stress-induced seismic velocity changes on anisotropic rocks. By introducing pre-existing cracks with preferential orientations in bonded-particle assemblies, the transverse isotropic structure of the Whitby Mudstone is simulated. Using power-law distributed aperture and calibrated micro-properties, we successfully reproduce stress-dependent velocity changes on Whitby Mudstones with different anisotropic angles in relation to the applied loads. The proposed model also duplicates the directional dependence of wave speed with respect to the bedding plane as expected theoretically. The numerical models show that velocity increase results from the closure of pre-existing cracks due to load increase. Direct relations are established between velocity changes and opened crack density (or crack closure), which displays a similar tendency compared with theoretical predictions. This relation can be used to quantify the micromechanisms behind the velocity changes. The proposed model provides the ability to directly examine the micro-processes underlying velocity changes.

Seismic velocity recovery following the 2015 Mw 7.8 Gorkha earthquake, Nepal: Towards a coupled vision of damage and hydrological-induced velocity variations

2021 ◽  
Author(s):  
Luc Illien ◽  
Christoph Sens-Schönfelder ◽  
Christoff Andermann ◽  
Odin Marc ◽  
Kristen Cook ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Seismic Velocity ◽  
Monsoon Season ◽  
Seismic Interferometry ◽  
Linear Superposition ◽  
Gorkha Earthquake ◽  
Ground Shaking ◽  
Velocity Variations ◽  
Velocity Changes ◽  
Induced Velocity

<p>Following the passage of seismic waves, most geomaterials experience non-linear mesoscopic elasticity (<em>NLME</em>). This is described by a drop in elastic moduli that precedes a subsequent recovery of physical properties over a relaxation timescale. Thanks to the development of seismic interferometry techniques that allows for the continuous monitoring of relative seismic velocity changes <em>δv</em> in the subsurface, observations of <em>NLME</em> (<em>δv</em><sub><em>NLME</em></sub>) in the field are now numerous. In parallel, a growing community uses seismic interferometry to monitor velocity changes induced by seasonal hydrological variations (<em>δv<sub>hydro</sub></em>). Monitoring of these variations are often independently done and a linear superposition of both effects is mostly assumed when decomposing the observed <em>δv</em> signal (<em>δv</em> =  <em>δv<sub>NLME</sub></em> + <em>δv<sub>hydro</sub></em>). However, transient hydrological behaviour following co-seismic ground shaking has been widely reported in boreholes measurements and streamflow, which suggests that  <em>δv<sub>hydro</sub></em> may be impacted by the transient variation of material properties caused by <em>NLME</em>. In this presentation, we attempt to characterize the relative seismic velocity variations <em>δv</em> retrieved from a small dense seismic array in Nepal that was deployed in the aftermath of the  2015 Mw 7.8 Gorkha earthquake and that is prone to highly variable hydrological conditions. We first investigated the effect of aftershocks in computing <em>δv</em> at a 10-minute resolution centered around significant ground shaking events. After correcting <em>δv</em> for <em>NLME</em> caused by the Gorkha earthquake and its subsequent aftershocks, we test whether the corresponding residuals are in agreement with the background hydrological behaviour which we inferred from a calibrated hydrological model. This is not the case and we find that transient hydrological properties improve the data description in the early phase after the mainshock. We report three distinct relaxation time scales that are relevant for the recovery of seismic velocity at our field site:  <strong>1.</strong> A long time scale activated by the main shock of the Gorkha earthquake (~1 year) <strong>2.</strong> A relatively short timescale (1-3 days) that occurs after moderate aftershocks. <strong>3.</strong> An intermediate timescale (4-6 months) during the 2015 monsoon season that corresponds to the recovery of the hydrological system. This timescale could correspond to an enhanced permeability caused by Gorkha ground shaking. Our study demonstrates the capability of seismic interferometry to monitor transient hydrological properties after earthquakes at a spatial scale that is not available with classical hydrological measurements. This investigation demands calibrated hydrological models and a framework in which the different forcing of <em>δv</em> are coupled.</p>

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