Double-couple seismic source
= Double-couple seismic source
A <double-couple seismic source> has a moment <tensor> proportional to $\mathbf b\otimes\mathbf n+\mathbf n\otimes\mathbf b$, with the slip direction $\mathbf b$ perpendicular to the <fault plane>'s normal $\mathbf n$. Its <eigenvalues> are proportional to $(1,0,-1)$. A general symmetric <seismic moment tensor> need not have this restricted form.