Use of in situ fiber optic sensors to characterize highly heterogeneous elastic displacement fields in fractured rocks

Abstract

Fractured and porous rock masses undergo complex deformations relating to geological, mechanical and hydrological processes, such as plate tectonics, earthquakes, earth tides, and the engineering design of structures in and on rock masses. The distribution of stresses in the earth’s crust governs the deformation field within and on the surface of geological systems. In turn, the rock stiffness, the presence of faults and others discontinuities, the topographical variations, the pore pressures, body forces and tectonic forces affect the stresses distribution in the earth [1]. Under basic loading or unloading such as overburden loads, tectonics forces, underground excavation, fractured rock masses generally deform according to a complex mechanical or hydromechanical behavior [1,2]. Displacements are first localized along pre-existing discontinuities, and then propagate within the porous rock matrix [2,3]. Along discontinuity planes, the displacements are generally of high magnitude and instantaneous, while displacements of the rock matrix are generally of lesser magnitude and slower. Thus, in active zones, deformation changes within fractured rocks present a large frequency range and can be both static and dynamic. Static changes involve static deformations that can be produced by volcanoes, tectonic sources, hydrologic effects; while dynamic changes are best represented by seismic waves produced by earthquake sources [4]. Geodesy has been the classical field measurements method for static changes and seismology for