Investigating the lithospheric velocity structures beneath the Taiwan region by nonlinear joint inversion of local and teleseismic P wave data: Slab continuity and deflection

The interaction between two flipping subduction systems shapes the complicated lithospheric structures and dynamics around the Taiwan region. Whether and in what form the Eurasian Plate subducts/deforms under Taiwan Island is critical to the debate of tectonic models. Although an east dipping high-velocity anomaly down to a depth below 200 km has been reported previously, its detailed morphology remains uncertain and leads to different interpretations. With a two-step strategy of nonlinear joint inversion, the slab images of the Eurasian Plate were retrieved in a geometry that is hyperthin in the south, becoming massive and steeper in the central, and severely deformed in the north. The possible depth and dimension of a slab break were also investigated through synthetic tests of whether the slab had torn. Moreover, the slab deflection found at ~23.2°N latitude seems to correspond to where the nonvolcanic tremors and recent NW-SE striking structures have occurred in southern Taiwan. Key Points High-resolution lithospheric images are retrieved by a two-step joint inversionThree-dimensional geometry of the east subducting slab under Taiwan is establishedA possible slab deflection is observed at around latitude 23.2°N