Shear dilatancy in rock and precursory changes in seismic velocities

Previous studies examining the relationship between the groundwater table and seismic velocities have been guided by empirical relationships only. Here, we develop a physics-based model relating fluctuations in groundwater table and pore pressure with seismic velocity variations through changes in effective stress. This model justifies the use of seismic velocity variations for monitoring of the pore pressure. Using a subset of the Groningen seismic network, near-surface velocity changes are estimated over a four-year period, using passive image interferometry. The same velocity changes are predicted by applying the newly derived theory to pressure-head recordings. It is demonstrated that the theory provides a close match of the observed seismic velocity changes.

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Seismic velocities of granulite-facies xenoliths from Central Ireland: Implications for lower crustal composition and anisotropy

Tectonophysics ◽

10.1016/j.tecto.2005.07.003 ◽

2005 ◽

Vol 407 (1-2) ◽

pp. 81-99 ◽

Cited By ~ 21

Author(s):

Riana van den Berg ◽

J. Stephen Daly ◽

Matthew H. Salisbury

Keyword(s):

Granulite Facies ◽

Seismic Velocities ◽

Crustal Composition ◽

Lower Crustal

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Gaussian beam migration

Geophysics ◽

10.1190/1.1442788 ◽

1990 ◽

Vol 55 (11) ◽

pp. 1416-1428 ◽

Cited By ~ 293

Author(s):

N. Ross Hill

Keyword(s):

Gaussian Beam ◽

Wave Field ◽

Seismic Source ◽

Velocity Model ◽

Downward Continuation ◽

Gaussian Beams ◽

Seismic Velocities ◽

Migration Method ◽

Gaussian Beam Migration ◽

Lateral Variations

Just as synthetic seismic data can be created by expressing the wave field radiating from a seismic source as a set of Gaussian beams, recorded data can be downward continued by expressing the recorded wave field as a set of Gaussian beams emerging at the earth’s surface. In both cases, the Gaussian beam description of the seismic‐wave propagation can be advantageous when there are lateral variations in the seismic velocities. Gaussian‐beam downward continuation enables wave‐equation calculation of seismic propagation, while it retains the interpretive raypath description of this propagation. This paper describes a zero‐offset depth migration method that employs Gaussian beam downward continuation of the recorded wave field. The Gaussian‐beam migration method has advantages for imaging complex structures. Like finite‐difference migration, it is especially compatible with lateral variations in velocity, but Gaussian beam migration can image steeply dipping reflectors and will not produce unwanted reflections from structure in the velocity model. Unlike other raypath methods, Gaussian beam migration has guaranteed regular behavior at caustics and shadows. In addition, the method determines the beam spacing that ensures efficient, accurate calculations. The images produced by Gaussian beam migration are usually stable with respect to changes in beam parameters.

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Seismic cone penetration test and seismic tomography in permafrost

Canadian Geotechnical Journal ◽

10.1139/t04-026 ◽

2004 ◽

Vol 41 (5) ◽

pp. 796-813 ◽

Cited By ~ 19

Author(s):

Anne-Marie LeBlanc ◽

Richard Fortier ◽

Michel Allard ◽

Calin Cosma ◽

Sylvie Buteau

Keyword(s):

Seismic Tomography ◽

Dynamic Properties ◽

Cone Penetration Test ◽

The Body ◽

Body Waves ◽

Reconstruction Technique ◽

Seismic Velocities ◽

Penetration Test ◽

Cone Penetration ◽

Seismic Cone Penetration Test

Two high-resolution multi-offset vertical seismic profile (VSP) surveys were carried out in a permafrost mound near Umiujaq in northern Quebec, Canada, while performing seismic cone penetration tests (SCPT) to study the cryostratigraphy and assess the body waves velocities and the dynamic properties of warm permafrost. Penetrometer-mounted triaxial accelerometers were used as the VSP receivers, and a swept impact seismic technique (SIST) source generating both compressional and shear waves was moved near the surface following a cross configuration of 40 seismic shot-point locations surrounding each of the two SCPTs. The inversion of travel times based on a simultaneous iterative reconstruction technique (SIRT) provided tomographic images of the distribution of seismic velocities in permafrost. The Young's and shear moduli at low strains were then calculated from the seismic velocities and the permafrost density measured on core samples. The combination of multi-offset VSP survey, SCPT, SIST, and SIRT for tomographic imaging led to new insights in the dynamic properties of permafrost at temperatures close to 0 °C. The P- and S-wave velocities in permafrost vary from 2400 to 3200 m/s and from 900 to 1750 m/s, respectively, for a temperature range between 0.2 and 2.0 °C. The Young's modulus varies from 2.15 to 13.65 GPa, and the shear modulus varies from 1.00 to 4.75 GPa over the same range of temperature.Key words: permafrost, seismic cone penetration test, vertical seismic profiling, seismic tomography, dynamic properties.

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Thermal regime of the lithosphere in the Canadian ShieldThis article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and the evolution of a continent.

Canadian Journal of Earth Sciences ◽

10.1139/e09-059 ◽

2010 ◽

Vol 47 (4) ◽

pp. 389-408 ◽

Cited By ~ 17

Author(s):

Claire Perry ◽

Carmen Rosieanu ◽

Jean-Claude Mareschal ◽

Claude Jaupart

Keyword(s):

Heat Flow ◽

Heat Generation ◽

Seismic Refraction ◽

Surface Heat ◽

Canadian Shield ◽

P Wave ◽

Seismic Velocities ◽

Flow Measurements ◽

Surface Heat Flow ◽

Mantle Heat Flow

Geothermal studies were conducted within the framework of Lithoprobe to systematically document variations of heat flow and surface heat production in the major geological provinces of the Canadian Shield. One of the main conclusions is that in the Shield the variations in surface heat flow are dominated by the crustal heat generation. Horizontal variations in mantle heat flow are too small to be resolved by heat flow measurements. Different methods constrain the mantle heat flow to be in the range of 12–18 mW·m–2. Most of the heat flow anomalies (high and low) are due to variations in crustal composition and structure. The vertical distribution of radioelements is characterized by a differentiation index (DI) that measures the ratio of the surface to the average crustal heat generation in a province. Determination of mantle temperatures requires the knowledge of both the surface heat flow and DI. Mantle temperatures increase with an increase in surface heat flow but decrease with an increase in DI. Stabilization of the crust is achieved by crustal differentiation that results in decreasing temperatures in the lower crust. Present mantle temperatures inferred from xenolith studies and variations in mantle seismic P-wave velocity (Pn) from seismic refraction surveys are consistent with geotherms calculated from heat flow. These results emphasize that deep lithospheric temperatures do not always increase with an increase in the surface heat flow. The dense data coverage that has been achieved in the Canadian Shield allows some discrimination between temperature and composition effects on seismic velocities in the lithospheric mantle.

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