3D Structure of the East Pacific Rise


    The ARAD 3-D (Anatomy of  a Ridge Axis Discontinuity) EW9707 cruise was undertaken in September and October 1997 to provide both refelction and wide-angle seismic data for the study of the overlapping spreading centre (OSC) at  9 degrees 3 minutes N  on the  East Pacific Rise. The project is a joint endeavour between the University of Cambridge / BIRPS and the Scripps Institute of Oceanography (SIO). The significance of the experiment lies in the fact that it was the first truly 3-D survey of an OSC.
In Cambridge we are attempting to determine the large scale 3-D velocity structure of the OSC by using recordings of  the densely spaced airgun shots by OBS's. The seismic images obtained will be free from unwanted artefacts that would otherwise be included in traditional 2-D profiles.

 This bathymetric map shows the overlapping spreading centre at  9degrees 3minutes N. YThe locations of the Ocean Bottom Seismometers (OBS's) are indicated with the grid marking where 201 parallel MCS lines with a spacing of 100m were shot  during the EW9707 cruise. The numbered instruments  were designed and built at Cambridge.

Two contradicting models of  a non-transform fault


Model A:

Two limbs of the ridge segments show decline of magmatic supply towardsd the ridge axis  discontinuity. (MacDonald et al 1984)

Model B:

Region of extensive partial melt under the overlap basin (Lonsdale 1983)

  This page last updated on May 6th 1998