3-D ROTATION OF DOUBLE-COUPLE EARTHQUAKE SOURCES

We discuss 3-D rotations by which one double-couple earthquake source can be rotated into another arbitrary double-couple. Due to the symmetry of double-couple sources, there are four such rotations. An algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3-D rotation of double-couple earthquake sources, i.e., for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another. This algorithm may be used in a wide variety of studies of stress field causing earthquakes, investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region, etc. The same inversion algorithm can be used to study the 3-D rotation of any symmetric second-rank tensor, such as the stress or strain tensor.