S-wave velocity uppermost mantle structure around beneath the Central Mariana subduction zone inferred from ambient noise tomography

Understanding the structure of the subduction zones is crucial for unraveling water transport mechanisms to the mantle, as the subducting slab serves as the primary channel for water entering the deep Earth. The Central Mariana subduction zone, where some of the oldest oceanic crust is subducting, is characterized by serpentinization in the fore arc evidenced by the presence of serpentinite mud volcanoes, arc volcanism driven by slab-released volatiles, and the formation of new oceanic lithosphere at back-arc spreading centers. In this study, we estimated fundamental-mode Rayleigh-wave group- and phase-velocity dispersion curves for periods from 3 to 35 s, as well as first overtone Rayleigh-wave group- and phase-velocity dispersion curves for periods from 4 to 7 s and from 5 to 13 s, using continuous seismic data from 32 ocean-bottom seismometers and 20 island stations. Additionally, group and phase velocities between asynchronous station pairs were determined using the C3 method. By jointly inverting the multimode Rayleigh-wave dispersion curves, we calculated an S-wave velocity model with resolutions down to 100 km depth, using a 3D reference model based on Crust1.0 and ak135 incorporating modified Moho depth and topography from seismic refraction data. Our results reveal low-velocity anomalies along the slab down to ~40 km depth, indicative of serpentinization, as well as beneath the volcanic arc (60-90 km depth) and the back-arc spreading center (10-30 km depth). Notably, a connection between the low-velocity anomalies beneath the arc and the back-arc spreading center is also observed.