Mesures géophysiques en laboratoire

Mesures géophysiques en laboratoire

Intervenant : Coefficient Crédits ECTS Heures UE
Michael HEAP 1 3 25 obligatoire

Travaux dirigés en anglais

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1/ Dynamic elastic moduli and Vp/Vs ratio

Elastic moduli of rock are fundamental physical properties. In the geosciences, the use of elastic moduli is ubiquitous. Knowledge of rock elastic moduli is important for (1) the reliable modelling of ground deformation at volcanic edifices, (2) the calibration of damage mechanics criteria and the development of time-to-failure laws, (3) the understand of dyke propagation and arrest, (4) understanding stress rotations around fault zones, amongst many more. In this TP the students measure the dynamic elastic moduli of several crustal rock types.

2/ The attenuation of seismic waves

An important aspect of the distribution of seismic waves will be approached in this TP: their attenuation within a heterogeneous medium. Attenuation is the gradual loss in intensity of any kind of through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water. Likewise, the behaviour of brittle rock is not perfectly elastic. Therefore, during the propagation of seismic waves through rock, energy is lost and the seismic signals are attenuated.

3/ Quantitative microcrack analyses for rock

Quantitative microcrack analysis is a powerful tool. It has both field applications, e.g. assessing the crack damage surrounding a large fault zone and laboratory applications, e.g. assessing the crack damage in experimentally deformed specimens. The combined integration of these two analyses yields valuable information, key to understanding geophysical problems in nature.In this TP, the students perform quantitative microstructural analysis on samples of sandstone and not only calculate at their microcrack densities, but also their microcrack anisotropies.

4/ Image analysis: introduction to ImageJ

Image analysis has become an increasingly important tool in the geosciences, a result of the increasing use of X-ray computed tomography to study rock microstructure. In this TP the students use ImageJ to study the microstructure of various rocks, some of which contain interesting microstructural features.

5/ The electrical conductivity of rocks

The goal of this TP is to measure the electrical conductivity of rocks saturated in salt solutions. The electrical properties of rocks are related to microstructural characteristics of porous networks, particularly the inner surface and porosity of rocks. The uses of these data are far-reaching. They are even used to assess volcanic hazards!

6/ Water permeability in sand

In this TPthe students study the hydraulic properties of porous media. Permeability is an intrinsic property of porous media and characterizes the ease with which fluid can flow through the pore network of porous material. This is a critical parameter in geophysics in many areas, both fundamental and applied. It may include transportation problems of fluid in the crust, the recovery of natural resources (e.g. oil and geothermal), problems related to water supply populations (e.g. hydrogeology), and also the problems of underground storage of waste pollutants. In all these areas, the permeability is the key factor that controls the short- or long-term geological problems. In practice, permeability measurements on rock require fairly large equipment to measure because the values are relatively low. However, for highly porous media such as sand, it is possible to use a simple device that can highlight the phenomenology of flow in porous media.

7/ Capillary imbibition in rock

Capillary imbibition is a transport phenomenon in porous rocks, the understanding of which is of extreme importance in many fields such as groundwater engineering, petroleum engineering, soil physics, civil engineers, engineering geology and building materials. In this TP the students investigate capillary imbibition in sandstone and limestone.

8/ Rheology

The understanding of the rheology of geomaterials is fundamental in the study of how the Earth deforms. At a certain depth within the Earth’s crust, below the brittle-ductile transition, rock responds to an applied force with plastic flow, rather than brittle faulting. This is the result of the increase in temperature and pressure with depth. The study of the flow of matter is called rheology. Rheology is keenly studied by a range of geoscientists. For example, for volcanologists, high-viscosity felsic magma will create a tall, steep stratovolcano, because it cannot flow far before it cools, while low-viscosity mafic lava will create a wide, shallow-sloped shield volcano.Temperature and pressure certainly influence the rheology of thegeomaterials, but the nature of the material can also exert an important effect (just like how rock microstructure can influence brittle deformation). In this TP the students perform viscosity measurements on plasticine.

9/ Transport of a pollutant

Understanding the factors that control the flow of water in soils and rocks in the subsurface has led to the development of one of the most important areas of Earth sciences:hydrology.Although the basic principles of fluid mechanics are applicable in hydrology, the nature of flows in the subsurface is complicated by geological processes that cause significant spatial variations (heterogeneity) in natural water systems.In this TP,the students address a number of important problems related to the study and exploitation of groundwater (piezometriclevel, dispersion of contaminants). In this subject, the use of models is very important as in-situ measurements must cover a wide area and are therefore very time consuming.