From field to laboratory, study of the elastic properties of basalt

• Main Author: Adelinet, Mathilde
• Other Authors: Laboratoire de Planétologie et Géodynamique - Géosciences Le Mans (LPG - Le Mans), Laboratoire de Planétologie et Géodynamique UMR 6112 (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL), Université du Maine, Laurent Geoffroy
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2010
• Subjects: basalt; elastic properties; geomechanics; geophysics; frequency effect; iceland; basalte; propriétés élastiques; géomécanique; géophysique; effet de fréquence; squirt-flow; islande; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Reykjanes; Iceland; Islande
• Online Access: https://theses.hal.science/tel-00672425; https://theses.hal.science/tel-00672425/document; https://theses.hal.science/tel-00672425/file/phd_adelinet_2010.pdf

Nearly 60 % of the Earth surface is composed by basaltic rocks which form the upper part of the oceanic crust. These PhD works focus on the elastic properties of basalt at several spatial scales : field scale, sample scale and porosity microstructure scale. With its active hydrothermalism Iceland appears as the ideal natural laboratory to study the interactions existing between basalts, fluids and fracturing at a large scale. We first begin by the study of a paleosite of hydrothermal fluid flow which took place in a basaltic pile. Some evidence of hydrofracturing are identified. We also investigate the porosity of the different materials associated to the hot fluid flow. The second part of the field study is based on microseismicity surveys on the Reykjanes Peninsula which is an active area in Iceland. The most important results is those deduced from inverting the tomography data obtained by C. Dorbath in 2005. By applying an effective medium theory to seismic velocities we have attempted to estimate the crack density and aspect ratio of the Icelandic crust at this place. We have show that areas characterized by a strong P-waves velocities anomaly were characterized by high crack density and low aspect ratio at 6 km depth. We have also investigated the effect of the fluid compressibility on the crack parameters with depth. The sample scale is investigated through two studies. The first one is the investigation of three different modes of deformation in an Icelandic basalt by using laboratory seismological tools (elastic waves and acoustic emissions) and scan imaging. first of all we show that at low effective pressure (5 MPa) an axial loading induces a shear failure in the basalt with a classical angle of about 45°. On the contrary at higher effective pressures (75 MPa and more) an increasing of the axial stress induces a localization of the deformation in the centre part of the sample. Focal mechanisms of the acoustic emissions reveal an important part of compression events (mode I rupture) suggesting pore ...