Correlated shear and bulk moduli to 1400 km beneath the Mediterranean region

We present a new model for the shear and compressional wave velocity structure of the Mediterranean plate boundary region. The model is obtained by a combined inversion of S and P data, where we solve in one single step for shear wave and bulk sound velocity variations. The ratios between the types of seismic velocities inferred from the combined inversion constrain the origin of heterogeneity. Our model is dominated by fast anomalies from subducted oceanic lithosphere. We found that only a slight amount of bulk sound velocity heterogeneity is required to explain the combined set of P and S data. Thus, compressional wave velocity anomalies are dominated by shear modulus heterogeneity and the ratio between bulk sound and shear wave velocity heterogeneity suggests a predominantly thermal origin.