New Constraints on the Complex Subduction and Tearing Model of the Cocos Plate Using Anisotropic Pn Tomography

To better understand the structure and process of the Cocos plate subduction, we obtained the first Pn velocity and anisotropy model of the uppermost mantle in southern Mexico using the Pn tomography method and new ISC‐EHB data. This study confirms that the subducted Cocos oceanic plate exhibits mid‐oceanic ridge‐perpendicular anisotropy, and there is an arc‐parallel anisotropic structure beneath the subduction arc. The variation of the Pn velocity and anisotropy structure at the east and west ends of the flat‐slab subduction zone in the Guerrero area provide new and clear seismological images for a plate‐tearing model which might be caused by the Orozco and O'Gorman fracture zones. The Pn low‐velocity and trench‐perpendicular anisotropic structure found north of the flat‐slab subduction zone support the slab retreat model of the Central Cocos plate. The Pn structure supports the existence of tearing corresponding to Teuhantepec Ridge in the Cocos plate beneath the Isthmus of Tuxtlas. Our study provides a reliable tomography basis and new constraints for a complicated subduction dynamics process in the southern Mexico subduction zone. Plain Language Summary The collision and subduction of the Cocos and North American plates created a complex geological structure in southern Mexico. Although some scholars proposed that there are some tears in the subducted Cocos slab based on the research of seismic parameters, the support of seismic tomography research for tear models is insufficient. Here, we applied a unique Pn tomography method and obtained the first Pn velocity and anisotropy model of the uppermost mantle in southern Mexico. The study clarified the mid‐oceanic ridge‐perpendicular anisotropy of the Cocos oceanic plate and the trench‐parallel anisotropy beneath the subduction arc. The spatial variations in Pn velocity and anisotropic structure in southern Mexico provide new seismological constraints on the tears of the subducted Cocos plate corresponding to fracture zones. The observed low Pn velocity beneath the Trans‐Mexican Volcanic Belt and the northern area and the trench‐perpendicular anisotropy support the retreat model of the Central Cocos plate. Our study provides a new and reliable tomography basis for a complicated subduction dynamics process in the southern Mexico subduction zone and provides new constraints for a slab‐tearing model corresponding to the fracture zones and the slab retreat model of the Central Cocos plate. Key Points The first