Joint inversion of body wave arrival times and surface wave dispersion data for the subduction zone velocity structure of central Chile

The Chilean Pampean flat slab subduction segment is characterized by the nearly horizontal subduction of the Nazca Plate within the depth range of 100-120 km. Numerous seismic tomography studies have been conducted to investigate its velocity structure; however, they only use either seismic body wave data or surface wave data. As a result, the existing velocity models in the region may have relatively large uncertainties. In this study, we use body wave arrival times from earthquakes occurring in the central Chile between 2014 and 2019, and Rayleigh wave phase velocity maps at periods of 5-80 s from ambient noise Empirical Green's functions in Chile. By jointly using body wave arrival times and surface wave dispersion data, we refine the Vs model and improve earthquake locations in central Chile subduction zone. Compared to previous velocity models, our velocity model better reveals an eastward dipping high-velocity plate representing the subducting Nazca Plate, which is 40-50 km thick and is more consistent with the slab thickness estimated by receiver function imaging and thermal modeling. Overall, the intraslab seismicity distribution spatially correlates well with the slab high velocity anomalies except for along the subduction paths of the Copiapó Ridge and Juan Fernández Ridge. Additionally, parallel low-velocity stripes are imaged beneath the subducting plate, which are likely associated with the accumulated melts. The joint inversion velocity model also resolves widespread low-velocity anomalies in the crust beneath the Central Volcanic Zone of the central Andes, likely representing crustal magma chambers for various volcanoes.