Monitoring of fracture propagation by quartz tiltmeters

The growth of a hydrofracture can be monitored by observation of the ensuing deformation of the earth's surface. The field data are processed and analyzed to yield a characterization of the deformation source. Several methods are used for measuring the surface deformation. Geodetic techniques are used for monitoring slow deformation over large areas, where tiltmeters may be used to complement geodetic networks by providing continuous records. In this paper, two different case studies are presented in which tiltmeters are used for measuring surface deformation. The first case deals with measurements of surface tilts obtained during an induced hydraulic fracture experiment. The fracture characteristics are obtained by comparing the measured deformation with those provided by a mathematical model. Nonlinear inversion of surface tilts gave estimates of the fracture geometry: depth, length, and thickness. The second case deals with tilts measured during a naturally induced hydraulic fracture in a volcanic area. The analysis of field data enabled good understanding of the volcano behavior.