Double-couple radiation pattern ($A_P=2n_1{n}_2,{\mathbf{A}}_S=(n_2,n_1,0)-2n_1{n}_{2}n$)

For the seismic moment tensor $M=e_1{e}_2^{\mathsf{T}}+e_2{e}_1^{\mathsf{T}}$, source differentiation of the outgoing elastodynamic Green tensor gives $A_P=n^{\mathsf{T}}Mn$ and ${\mathbf{A}}_S=(I-n{n}^{\mathsf{T}})Mn$. In the $x_1{x}_2$ plane the signed radial P wave and tangential S wave factors are $\sin 2\varphi$ and $\cos 2\varphi$. The full S wave magnitude squared is $n_1^2+n_2^2-4n_1^2{n}_2^2$.

For orthogonal slip and fault-normal unit vectors $s,n$, the P radiation amplitude is $2M_0(\hat{r}\cdot s)(\hat{r}\cdot n)$. Its zeros are the two planes normal to $s$ and $n$, producing four alternating polarity quadrants.