Much of the relief of the abyssal hills covering the ocean
basins is believed to originate from faulting of oceanic crust at mid-
ocean ridges. The timescale over which faults grow is controversial,
however, with some authors arguing that faults continue to grow in
places for 0.5 m.y. or more based on increasing relief of fault
scarps with distance from ridge axes. We examine Deep Tow
profiler records of the Galapagos Spreading Centre, in which
basement reflections allow scarp relief to be measured beneath the
sediment cover, and find that relief does not increase but decreases
systematically to 40 km off-axis (1.5 Ma seafloor). Since reversal
of fault offsets is unlikely in this tectonic setting, we interpret this
result as indicating that variations in fault statistics could reflect
temporal variations in the tectonic or volcanic state of the ridge
crest, not necessarily progressive fault growth with age as
previously assumed. Resolving the issue of fault longevity will
therefore require independent data on the timing of fault growth and
distribution of present growth activity. We suggest some possible
alternative indicators of fault longevity and discuss more generally
the implications of volcanic flows to studies of faulting at ridges.
Mitchell, N. C., and R. C. Searle, "Fault scarp statistics at the Galapagos spreading centre
from Deep Tow data", Marine Geophysical Researches, 20, 183-193, 1998.