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Cracked, Porous Rocks and Fluids: Moon and Earth Paradox

Laboratoire de Géologie, Ecole Normale Supérieure/CNRS, UMR8538, PSL Research University, 75005 Paris, France
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Minerals 2019, 9(11), 693; https://doi.org/10.3390/min9110693
Received: 14 October 2019 / Revised: 6 November 2019 / Accepted: 7 November 2019 / Published: 9 November 2019
(This article belongs to the Special Issue Mineral Physics—In Memory of Orson Anderson)
Elastic wave velocities are key parameters in geosciences. In seismology at a large scale, or in seismic exploration at a more local and shallower scale, they were the main source of information for a long time. At the time of the Apollo mission, Anderson explained the unexpected result of very low velocities in Moon surface rocks by an intense cracking resulting from meteoritic impacts. Yet, it was also known that the Q factor was high. This could appear as a paradox. In the shallow layers of the Earth, rocks are porous. These shallow layers are of major importance in the Earth since they contain fluids. This is why velocities are higher and Q values lower in the Earth’s shallow layers than in the Moon’s shallow layers. Cracks have a determining effect on elastic properties because they are very compliant. Fluids also play a key role. Combining poroelasticity and effective elasticity, two independent theories much developed since the time of the Apollo mission, makes it possible to revisit the contrasting results observed in the Moon case and in the Earth case. Experimental results obtained on cracked synthetic glass show that dry cracks result in a strong decrease in velocity. On the other hand, saturated porous limestones exhibit a strong frequency-dependent attenuation when thermally cracked. The presence of fluid is the key factor.
Keywords: rock physics; pores; cracks; fluids; effective medium theory; poroelasticity rock physics; pores; cracks; fluids; effective medium theory; poroelasticity
MDPI and ACS Style

Borgomano, J.V.; Fortin, J.; Guéguen, Y. Cracked, Porous Rocks and Fluids: Moon and Earth Paradox. Minerals 2019, 9, 693.

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