Figure 1
From: Seismic moment and volume change of a spherical source
Source representations. (a) A spherical source with purely outward radial expansion of Δs (S1), (b) a spherical crack source with outward and inward displacements (Δs and ds, respectively) along the spherical surface (S2), (c) an isotropic source with three mutually perpendicular vector dipoles (S3), and (d) a superposition of three mutually perpendicular tensile cracks (S4).