Seismic monitoring of shear stress on fractures/faults

Abstract

SummaryLaboratory experiments have shown that the static shear stress acting on a fracture displays a distinctive seismic signature. For plane P waves normally incident on a fracture, the application of a static shear stress results in converted, plane S waves. For incident S waves converted P waves are produced. The amplitude and polarity of these converted waves are directly related to the magnitude and direction of the static shear stress acting on the fracture. We use a numerical model to investigate the relationship between converted waves, fracture geometry and in-situ shear stress. This model can capture the response of fractured rocks to both dynamic and quasi-static stresses, allowing 'time-lapse' seismic simulations to be carried out across the fracture during changing stress conditions. Our simulations show that the anomalous scattering of seismic waves from sheared fractures is reproduced in this numerical model, making it an appropriate tool for further investigation of this phenomenon. It is hoped that this research will lead to the development of a quantitative tool for evaluating subsurface shear stress.