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The formation of a new ocean basin provides a unique observational window into the structure and deformation of the oceanic lithosphere. This study offers a detailed 1‐D vertically polarized shear‐wave velocity model of the young Japan Basin by interpreting S receiver functions, seafloor Rayleigh wave ellipticities and phase velocities in a Bayesian trans‐dimensional framework. The models suggest a distinct discontinuity in the mid‐lithosphere. Additional analyses indicate that the upper layer is characterized by strong positive radial anisotropy, while the lower layer is more isotropic. We interpret that the upper layer was formed during the back‐arc opening at 20–15 Ma, where the olivine lattice‐preferred orientation (LPO) fabric induced by passive upwelling contributes to the positive radial anisotropy. The lower, less anisotropic layer may be solidified after the sudden cessation of the opening. Small‐scale convection (SSC) from such a major tectonic event could randomize the LPO enough to weaken radial anisotropy before cooling down the asthenosphere, leaving a radially anisotropic discontinuity in the present‐day mid‐lithosphere. The proposed layered evolution history of the lithosphere beneath the Japan Basin illuminates an important role of the small‐scale convection in modifying the structural fabrics of the asthenosphere in terms of radial anisotropy. Such an SSC‐induced radial anisotropy drop could also occur at the base of the lithosphere in regions with ongoing seafloor spreading and enhance the velocity drop of horizontally polarized shear waves. Thus, the role of SSC is non‐negligible in explaining the sharpness of the Gutenberg discontinuity detected by SS precursors beneath the oceanic lithosphere. Plain Language Summary: The formation of the oceanic lithosphere is associated with a relatively simple mantle convection process called seafloor spreading, but may also be affected by more complex, localized processes such as small‐scale mantle convection. To decipher the evolution history of the lithosphere of the Japan Basin, the Sea of Japan, this study collects earthquake waveforms from broadband ocean‐bottom seismometers and offers a detailed 1‐D seismic structural model beneath the Japan Basin by interpreting the multiple seismological observables in a trans‐dimensional Bayesian framework. Our seismic velocity model and associated analysis reveal that the oceanic lithosphere of the Japan Basin is seismically more complex than expected. The upper and lower parts of the lithosphere show distinct seismic anisotropy properties. We propose a layered evolution model for the lithosphere of the Japan Basin, in which small‐scale convection followed a normal seafloor spreading, and resulted in a structural discontinuity in the present‐day mid‐lithosphere. The proposed model highlights the role of the small‐scale convection in modifying the structural fabrics of the asthenosphere in terms of radial anisotropy. Key Points: We construct detailed 1‐D Vsv models of the Japan Basin by trans‐dimensional inversion of multiple observables extracted from ocean‐bottom seismometers recordsOur analysis reveals a mid‐lithosphere discontinuity arising from strong positive radial anisotropy in the upper lithosphereA layered evolution mode associated with small‐scale convection is proposed for the lithosphere of the Japan Basin [ABSTRACT FROM AUTHOR]

In this study, a high‐resolution 3D lithospheric S wave velocity model of the Jiuyishan region is constructed by joint inversion of receiver function and ambient noise. Our Moho depth model reveals relatively thick crust (∼35 km) beneath the Yangtze block and thin crust (∼27 km) beneath the Cathaysia block. The model depicts a complex boundary between these blocks, roughly following the Chenzhou‐Linwu fault in the northern part but gradually curving westward in the southern part between the two blocks. The 3D S wave velocity model shows low‐velocity anomalies in the middle crust, as well as in the upper mantle, interpreted as evidence of asthenospheric upwellings in the upper mantle. These upwellings modify lithosphere structures by changing their temperatures and compositions, and may provide a heat source through the Chenzhou‐Linwu fault for the low‐velocity anomaly in the shallow part beneath Jiuyishan region. Plain Language Summary: The South China block, which is composed of the Yangtze and Cathaysia blocks, has undergone a series of intraplate orogenic episodes since the Neoproterozoic. Location of the southwestern boundary of the Yangtze and Cathaysia blocks has been ambiguous, and the local lithospheric structure is not well constrained. We construct a high‐resolution 3D lithospheric shear velocity model, which provides the first evidence suggesting that the Jiuyishan region is undergoing lithospheric modification. Our model depicts a complex boundary between these blocks, roughly following the Chenzhou‐Linwu fault in northern part but gradually curving westward in the southern part between the two blocks. Moreover, the shear wave velocity structure shows prominent low‐velocity anomalies in the middle crust as well as in the upper mantle. We interpret the low anomalies in mantle as asthenospheric upwellings, which may provide a heat source for the shallow low‐velocity anomaly. Key Points: High‐resolution lithospheric velocity structure as well as Moho depths in the Jiuyishan region are obtained from new seismic array dataBoundary between the Yangtze and Cathaysia blocks roughly follows the Chenzhou‐Linwu fault in the north but curves westward in the southThe asthenospheric upwellings beneath the Jiuyishan region may provide the heat source for a shallow low‐velocity anomaly [ABSTRACT FROM AUTHOR]

Situated in a transition zone between the Ordos basin and the Huabei basin, the Trans-North China Orogen (TNCO), or the central North China Craton, evolved as an extensional orogen during the late Mesozoic to Cenozoic, with Fenhe-Weihe Rift (FWR) developing in it in the Cenozoic. In this study, we construct a high resolution lithospheric model of TNCO by jointly interpreting the broadband surface wave dispersions derived from ambient noise and teleseismic surface wave data. The most significant features of the lithospheric mantle are the two separated low velocity anomalies beneath the northern and southern TNCO respectively. Considering that the Pacific slab subducted to the mantle transition zone with a gap under the Datong volcanic zone, and large-scale low-velocity mantle materials are ascending from the lower mantle through the slab gap, which is evidenced by teleseismic P wave tomography, we propose here that the northern TNCO was affected by the mantle upwelling from the lower mantle. On the contrary, the south TNCO was mainly modified from the dehydration reaction process of the stagnant Pacific slab. In the lower crust, we observe significant low velocities beneath the Datong volcanic field, which are interpreted as the recent magmatic underplating resulted from the ongoing mantle upwelling in the northern TNCO. In addition, the mantle upwelling has dominated the rifting process in the northern segment of the FWR. Although the passive rifting of the FWR propagated from south to north, the north FWR is under an active lithosphere thinning regime now. • High-resolution S wave velocity model of TNCO inverted from broadband Rayleigh wave dispersions. • Different causes for lithospheric LVZs in north and south TNCO and On-going lithospheric modification in the TNCO. • Transition from passive to active rifting in the northern segment of the FWR [ABSTRACT FROM AUTHOR]

The convergence between the Eurasian Plate and the Philippine Sea Plate results in rapid uplifting of the Taiwan Orogen. To study the mountain building in Taiwan, we present three transects of shear wave velocity across the Taiwan mountain belt with joint inversion of teleseismic Rayleigh wave H/V ratios and phase velocities derived from ambient noise tomography. The Particle Swarm Optimization algorithm is introduced into the joint inversion and is proved to be an efficient tool in solving the geophysical inverse problems. In determining the H/V ratios, cross-correlation techniques are used to reduce the non-great circle effects of the Rayleigh wave packets and to correct sensor misorientations. The cross-correlation techniques improve the accuracy of the H/V measurements, especially at the short periods. The observed up-to-middle crustal thickening in the central segment of the Central Range suggests lithospheric collision tectonism, whereas the lower crustal thickening in southern segment is proposed to be related to subduction of the Eurasian continental crust. In the north, however, no crust thickening is observed. The variations of the crust architecture along the axis of the Taiwan Orogen favor a close coupling relationship between mountain building and slab interactions in the mantle. Beneath the Central Range, the twist of the fate of the Eurasian continental crust from consumption in the south to collision in the central segment is proposed to be resulted from the slab breakoff beneath central Taiwan. • High-resolution shear wave velocity transects across the Taiwan Island from joint inversion. • Deflection of Rayleigh wave packet from the great-circle path. • Coupling of the mountain building with the subsurface slab interactions in Taiwan. [ABSTRACT FROM AUTHOR]