3‐D Plate Interaction Beneath the Active Taiwan Orogen Revealed by Source‐Side Seismic Tomography: Implications for Slab Breakoff and Orogenic Evolution

Abstract We employed an unconventional teleseismic tomographic inversion method, referred to as source‐side teleseismic tomography (SSTT), to enhance the resolution of 3‐D P‐wave velocity (Vp) structure beneath the active Taiwan orogenic belt down to a depth of ∼400 km. Unlike traditional teleseismic tomography, which uses travel‐time residuals from teleseismic events to local stations, we utilize travel‐time residuals from local earthquakes to distant stations. This method significantly increases the spatial sampling of ray paths at mantle depths due to the substantially larger number of local events distributed at depths and along subduction zones compared to the limited number of broadband stations confined to the surface. Our findings reveal detailed 3‐D geometry and interaction of the subducting Eurasian Plate (EP) and Philippine Sea Plate (PSP) beneath Taiwan. In the south, the high‐Vp anomaly, interpreted as the subducting EP, descends eastwardly down to a depth of 400 km at approximately 123°E longitude. Moving from central to northern Taiwan, the EP steepens and becomes detached at depths of 200–300 km. This slab detachment progressively widens northward, and extends beneath the northward‐dipping PSP. The detached EP segment beneath the PSP indicates its prior subduction location beneath the southern Ryukyu and supports the slab breakoff model rather than the lithospheric tear model. This newly derived model resolves the intricate 3‐D plate interaction between the EP and PSP that drives complex spatiotemporal tectonic processes of the Taiwan orogen, and demonstrates the efficacy of SSTT in enhancing mantle imaging in Taiwan and other seismically active regions.