Evidence of an upper mantle seismic anomaly opposing theCocos slab beneath theIsthmus ofTehuantepec,Mexico

Abstract

Subduction of the Cocos plate beneath southern Mexico is characterized by several unusual features, such as a discontinuous volcanic arc, unusual arc chemistry, and anomalously low topography of Tehuantepec Isthmus. Recent seismic images from both receiver functions and seismic tomography suggest that there may be an additional, opposing structure dipping to the southwest from the Gulf of Mexico, and these images have been previously explained by a southwest-dipping slab. However, standard models of the Caribbean tectonic history do not support this interpretation. To better define the Cocos slab's structure and the possible existence of a structure dipping in the opposite direction, dense seismic data across southern Mexico are used to form high-resolution seismic images, based on the 2-D generalized radon transform method, and to relocate regional earthquakes. Our images show the Cocos plate dipping at 30 to the northeast encounters the anomaly that is dipping in the opposite sense at 150 km depth. Relocated seismicity clearly delineates a Wadati-Benioff zone that marks the subducting Cocos plate. A cluster of seismicity also appears at 150 km depth which may be related to the subduction of the Tehuantepec ridge and/or to the imaged seismic structure with opposite polarity.

Shear Wave Splitting and Mantle Flow in Mexico: What Have we Learned?

“…(3) The coastline is farther away from the MAT than in the area located to the west, which implies the existence of a broad continental shelf. This is also the site where the enigmatic Yucatán slab was imaged in VEOX receiver functions (Kim et al, 2011(Kim et al, , 2014. It has been suggested that the Yucatán slab is a southwest-dipping structure opposing, and in fact cutting through, the longrecognized northeast-dipping Cocos slab (Kim et al, 2011).…”

“…The Yucatán slab is also inferred to exist in this region (Kim et al, 2011(Kim et al, , 2014. Receiver function images suggest that the Yucatán slab cuts off the Cocos slab and is thus expected to hinder 2-D mantle wedge flow for both systems (Kim et al, 2011).…”

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

“…Thus, this area has become an important laboratory for studying the structure and dynamic process of the subduction zone. Various studies have been conducted on the geophysical and geological structures in this region (Chen & Clayton, 2009; Ferrari, 2004; Ferrari et al., 1999, 2012; Gérault et al., 2015; Kim et al., 2010, 2014; M. Manea & Manea, 2008; Manea et al., 2013; Melgar & Pérez‐Campos, 2011; Pardo & Suarez, 1995; van Benthem, Govers, et al., 2013). Previous studies have recognized that the Cocos plate is moving and subducting toward the North American plate at different speeds, increasing from 5.2 mm/y in the west to 7.5 mm/y in the east.…”