Local earthquake (LE) tomography with joint inversion for P‐ and S‐wave velocities using structural constraints

In local earthquake (LE) tomography for P‐ and S‐wave velocities (or Vp/Vs ratios), constraints punishing deviations from a given Vp/Vs ratio are often used. In a synthetic model test we demonstrate that though such constraints inhibit unreasonable Vp/Vs ratio variations, they bias the resulting Vp/Vs ratios. As an alternative approach, structural constraints based on the cross‐product of the model gradients can be used to constrain the joint P‐ and S‐wave inversion. We show that the resulting models are as low in artifacts as if a Vp/Vs damping was used, but the resulting Vp/Vs ratios are less biased, which is important for a quantitative interpretation of physical properties and processes in the Earth.