Abstract

A recently developed near-bottom reflection profiling system has been used to obtain high resolution seismic sections across the Vema transform fault. At the western ridge–transform intersection deep-towed 3.5 kHz echo sounder data show evidence of fresh lava flows at the seabed within the nodal deep.

Over one kilometre of sediment fills the bottom of the ridge–transform intersection deep. Many strong, discontinuous reflectors within the sedimentary section caused by lava layers indicate that the intersection deep has been the site of sustained igneous activity. On the eastern side of the deep is a large, uplifted fault block created as the newly formed crust moved out of the spreading centre. Dipping strata within the fault block document back-tilting as the new crust is extended by normal faulting. Profiles across the active transform fault reveal that the zone of deformation throughout the one kilometre thick sediment column is narrow, suggesting that the location of the fault has remained stable throughout at least the last million years.

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