Fig. 6

A Cartesian coordinate system fixed to a seismic source. The \(x_{1}\)-axis is taken in the direction of fault slip \({\varvec{\nu}}\) and the \(x_{3}\)-axis is taken in the direction of fault normal \({\mathbf{n}}^{ - }\). The mutually orthogonal unit vectors, \({\mathbf{e}}_{r}\), \({\mathbf{e}}_{\theta }\) and \({\mathbf{e}}_{\phi }\), define the local coordinate system at a receiver point \((r,\theta ,\phi )\). The radial distance range of the wave packet traveling outward at a phase velocity \(c\) is indicated by \(c\Delta T\)