Azimuthal Anisotropy Tomography of the Southeast Asia Subduction System
A detailed 3‐D model of P wave isotropic velocity and azimuthal anisotropy beneath SE Asia is obtained by jointly inverting local earthquake arrival times and teleseismic relative travel‐time residuals. Our results show that the high‐velocity (high‐V) subducting Australian slab has penetrated throug...
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Veröffentlicht in: | Journal of geophysical research. Solid earth 2022-02, Vol.127 (2), p.n/a |
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Zusammenfassung: | A detailed 3‐D model of P wave isotropic velocity and azimuthal anisotropy beneath SE Asia is obtained by jointly inverting local earthquake arrival times and teleseismic relative travel‐time residuals. Our results show that the high‐velocity (high‐V) subducting Australian slab has penetrated through the mantle transition zone (MTZ) and reached a depth of ∼1,200 km beneath Sumatra, whereas the high‐V slab has subducted toward the north and trapped within the MTZ beneath Java. The Hainan mantle plume is revealed clearly as a significant low‐velocity anomaly beneath the MTZ, which extends down to the bottom of our model (∼1,600‐km depth). The upwelling of the Hainan plume is resisted by the stagnant slab in the MTZ, resulting in divergent fast‐velocity directions of azimuthal anisotropy beneath the stagnant slab. The detailed results of seismic tomography and azimuthal anisotropy provide important new information on the complex mantle structure and dynamics of the SE Asian region, in particular, the subducting slabs and the Hainan plume, as well as their interactions.
Plain Language Summary
The SE Asia curved subduction system is an ideal region to study plate tectonics and subduction dynamics due to the coexistence and interactions of the Hainan mantle plume and subducting slabs. However, detailed geometries and structures of the plume and slabs are still unclear because of the uneven distribution of seismic stations and earthquakes in SE Asia. In this work, we study the 3‐D seismic velocity structure beneath SE Asia by conducting P wave seismic tomography. We find that the Hainan plume upwelling is resisted by a stagnant slab in the mantle transition zone (MTZ, at depths of 410–660 km), generating divergent azimuthal anisotropies that are centered in significant low‐velocity zones beneath the MTZ. The coexistence of the mantle plume and the stagnant slab may have caused the complex tectonic history and geological features in SE Asia, such as many arc and back‐arc volcanoes, active intraplate volcanism, and widely distributed Cenozoic basalts.
Key Points
A high‐resolution 3‐D model of P wave velocity and azimuthal anisotropy beneath SE Asia is determined
Different slab geometries beneath Sumatra and Java are related to the lithosphere age of the subducting slab
The Hainan plume upwelling is resisted by a stagnant slab in the MTZ, causing divergent shape azimuthal anisotropies |
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ISSN: | 2169-9313 2169-9356 |
DOI: | 10.1029/2021JB022854 |