Ambient Noise Tomography Across the Taiwan Strait, Taiwan Island, and Southwestern Ryukyu Arc: Implications for Subsurface Slab Interactions.

The subduction flipping in the Taiwan region leads to complexities in the lithospheric structure. To better understand the arc‐continental collision process in this zone, we construct a 3‐D lithospheric model of the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc. In the middle to lower crust, low velocities are mainly located beneath the Ryukyu Trough and the rifted basins in the Taiwan Strait, and high velocities are imaged in the Kuanyin and Penghu Platforms. Likely, the Kuanyin and Penghu Platforms act as relatively strong barriers that block the persistent westward advance of the western deformation front of the Taiwan mountain belt, as manifested by shape of the deformation front that withdraws to the east in the basement highs. In the mantle, high velocities are observed beneath the Central Range and Ryukyu Arc, which is interpreted as the two oppositely oriented slab subductions, that is, subduction of the Philippine Sea slab in the northeast Taiwan and Eurasian slab subduction in south Taiwan. Based on the vertical transects through our 3‐D model, we find that the subduction polarity has flipped in north Taiwan, and the tectonic framework in central Taiwan is in the process of subduction polarity reversal. We also image significant low mantle velocities beneath the North Taiwan Volcanic Zone and Taihsi Basin, which may be related to the breakoff of the subducting Eurasian slab. In addition, we propose that the inherited weakness of the Taihsi Basin may have facilitated the slab breakoff in central Taiwan. Plain Language Summary: In this work we collect the seismic data recorded by seismic stations in and around the Taiwan orogen and build a high‐resolution lithospheric velocity model for an area including the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc by ambient noise tomography. The model exhibits low crust velocity anomalies in the Ryukyu Trough and rifted basins of the Taiwan Strait, and low velocities in the uppermost mantle beneath the North Taiwan Volcanic Zone and Taihsi Basin. Based on the tomographic images, we clearly find that the subduction polarity has been flipped in north Taiwan, and the tectonic framework in central Taiwan is in the process of subduction polarity reversal, which is in consistent with the geological observations. Key Points: A high‐resolution lithospheric model of the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc is obtained from ambient noise tomographySignificant low mantle velocities related to the breakoff of the subducting Eurasian slab are observed under the NTVZ and THBSubduction polarity reversal is ongoing in central Taiwan; the lithospheric scale weak THB facilitates the slab breakoff in central Taiwan [ABSTRACT FROM AUTHOR]