P-wave attenuation structure of the Lau back-arc basin and implications for mantle wedge processes

- The lowest QP (∼30) in the upper mantle is imaged beneath the Lau back-arc SCs.
- High P-wave attenuation anomalies dip to the deeper west away from the Tonga slab.
- These anomalies result from unusually high temperature and mantle melting.
- Low P-wave attenuation is found beneath the Tonga fore-arc.
- The P-wave attenuation shows a weak frequency dependence (α≈0.3).