Reflection and Transmission Coefficients for an Incident Plane Shear Wave at an Interface Separating Two Dissimilar Poroelastic Solids |
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| Authors: | Xu Liu Stewart Greenhalgh |
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| Institution: | 1. Department of Geology and Geophysics, University of Adelaide, Adelaide, 5005, Australia
2. Institute of Geophysics, ETH Zurich, Sonneggstrasse 5, 8092, Zurich, Switzerland
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| Abstract: | Using Biot’s poroelasticity theory, we derive expressions for the reflection and transmission coefficients for a plane shear wave incident on an interface separating two different poroelastic solids. The coefficients are formulated as a function of the wave incidence angle, frequency and rock properties. Specific cases calculated include the boundary between water-saturated sand and water-saturated sandstone and the gas–water interface in sand. The results show a very different interface response to that of an incident P wave. Plane SV wave incidence does not significantly excite the Biot slow P wave if the frequency of the wave is below the transition frequency. Above this frequency, an incident plane SV wave can generate a mode-converted slow Biot P wave which is actually a normal propagating wave and not highly attenuating as in the usual (diffusive) case. For an incident SV wave onto a gas–water interface, even at very high frequency, there is no significant Biot second P wave produced. For small incident angles, the gas–water interface is essentially transparent. With increasing angles, there can arise an unusual "definitive angle" in the reflection/transmission coefficient curves which is related to the change of fluid viscosity on both sides of the interface and provides a possible new means for underground fluid assessment. |
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