Shear‐wave splitting and anisotropy in the Charlevoix Seismic Zone, Quebec

During the month of August 1984 an experiment was undertaken in the Charlevoix Seismic Zone to test the hypothesis that shear‐wave splitting could be observed in a seismically active region. Seismograms, recorded by digital 3‐component seismographs, located very close to the epicentres of three earthquakes, showed shear‐wave splitting. The amount of splitting was estimated to be 1.6% to 2% of the shear wave velocity from particle motion diagrams. The average azimuth of the direction of polarization was 30°. These observations can be explained by the presence of vertical cracks striking 30° east of north, with a minimum crack density of ε = 0.03.