MASE tomography data showing the position of the flat slab. See cartoon view
Contours indicate seismic wave speed. Blue shows where waves travel faster, indicating the area is dense (subducting plate). Pink shows where waves travel slower, indicating the area is less dense (mantle).
The slab (purple line) begins with a shallow dive below Acapulco, then levels out almost to Mexico City. Below Mexico City it plunges steeply into the mantle and ends abruptly at a depth of about 500 km.
Note that active volcanoes occur above where the slab attains a depth of 100 km. [Modified from Perez-Campos et al., GRL 2008].