S-wave isotropic and radially anisotropic velocity structure around the Mariana Trench inferred from ambient noise tomography

At the Mariana Trench, the Pacific plate with increasing age to the east is subducting beneath Philippine Sea plate. This subduction zone includes a volcanic arc, back-arc spreading center and many serpentinite seamounts. The Central Mariana Trench is investigated by using seismic data from 32 OBSs and 20 stations deployed in islands. Cross-correlating ambient noise records between station pairs yields fundamental-mode Rayleigh- and Love-wave dispersion curves at periods from 3 s to 35 s and at periods from 3 s to 20 s, respectively and used a 3D reference model consisting of Crust1.0 and ak135 to obtain more accurate inversion results. In particular, we also estimate group velocities between asynchronous station pairs by using permanent stations on great circle as virtual sources. By jointly inverting Rayleigh- and Love-wave dispersion curves, we calculate an S-wave isotropic and radially anisotropic velocity model, which has resolutions down to 70 km depth for isotropic S-wave velocity model and down to 40 km depth for anisotropic model. Low velocity anomalies are imaged due to the serpentinization and volcanic arc and high velocity anomalies are caused by the stagnation of fore-arc material. On the other hand, negative radial anisotropy are observed dominantly down to 15 km depth, which may be caused by vertical dykes responsible for many seamounts in this region.