Comparisons between the rift systems of East Africa, Earth and Beta
Regio, Venus.
A. Foster and F. Nimmo, Earth Planet. Sci. Lett. 143, 183-196, 1996
The rift systems of southern East Africa and Beta Regio, Venus
are similar in a number of ways, The rifted East African and
Venusian lithospheres have effective elastic thicknesses of
similar to 30 km, suggesting that both lithospheres maintain
significant flexural strength during rifting. Both rift systems
have maximum fault segment lengths of similar to 100 km, The
effective elastic thickness and maximum fault segment length of
both rifts are greater than those seen in many other active
extensional regions on Earth, despite the high surface
temperatures on Venus, We suggest that the southern East
African and Venusian elastic thicknesses and maximum fault
segment lengths are due to stronger lithosphere. The rift
systems differ in the maximum width of their half graben, East
African half grabens are up to similar to 50 km wide, whilst
those on Venus are up to similar to 150 km wide, To support the
topography associated with such half grabens requires shear
stresses to act on the bounding faults, In East Africa the
greater elastic thickness (compared to most other terrestrial
extensional regions) means that wide half grabens can form
without requiring the shear stresses acting on the bounding
faults to be greater than the similar to 1-10 MPa (10-100 bars)
stress drop typically seen in earthquakes. However, on Venus
the absence of sediment infill, greater widths and larger
effective topographic steps of the half grabens require shear
stresses of up to similar to 80 MPa (800 bars) to act on the
bounding faults, This difference is significant; Venusian
faults must be stronger than those on Earth.
Francis' Page
Department of Earth Sciences
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nimmo@esc.cam.ac.uk
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