408 TECTONICS/Seismic Structure At Mid-Ocean Ridges Figure Example of a multichannel seismic line collected along the axis of the East Pacific Rise, showing the base of the extrusive crust (layer 2A) and the reflection from the top of the axial magma chamber (AMC) (A) The bathymetry of the ridge axis, with the location of the seismic profile indicated by the black line (B) The dashed lines on the seismic section mark the locations of very small offsets that are observed in the narrow depression along the axis where most active volcanism is concentrated From Carbotte SM, Ponce Correa G, and Solomon A (2000) Journal of Geophysical Research 105: 2737 2759