Structure of central and southern Mexico from velocity and attenuation tomography

Abstract

The 3D V p , V p / V s , P‐ and S‐wave attenuation structure of the Cocos subduction zone in Mexico is imaged using earthquakes recorded by two temporary seismic arrays and local stations. Direct P wave arrivals on vertical components and direct S wave arrivals on transverse components from local earthquakes are used for velocity imaging. Relative delay times for P and PKP phases from teleseismic events are also used to obtain a deeper velocity structure beneath the southern seismic array. Using a spectral‐decay method, we calculate a path attenuation operator t * for each P and S waveform from local events, and then invert for 3D spatial variations in attenuation ( Q p −1 and Q s −1 ). Inversion results reveal a low‐attenuation and high‐velocity Cocos slab. The slab dip angle increases from almost flat in central Mexico near Mexico City to about 30° in southern Mexico near the Isthmus of Tehuantepec. High attenuation and low velocity in the crust beneath the Trans‐Mexico Volcanic Belt correlate with low resistivity, and are probably related to dehydration of the slab and melting processes. The most pronounced high‐attenuation, low‐ V p and high‐ V p / V s anomaly is found in the crust beneath the Veracruz Basin. A high‐velocity structure dipping into the mantle from the side of Gulf of Mexico coincides with a discontinuity from a receiver functions study, and provides an evidence for the collision between the Yucatán Block and Mexico in the Miocene.