COMPARISONS BETWEEN THE RIFT SYSTEMS OF EAST-AFRICA, EARTH AND BETA-REGIO, VENUS

The rift systems of southern East Africa and Beta Regio, Venus are sim ilar in a number of ways, The rifted East African and Venusian lithosp heres have effective elastic thicknesses of similar to 30 km, suggesti ng that both lithospheres maintain significant flexural strength durin g rifting. Both rift systems have maximum fault segment lengths of sim ilar to 100 km, The effective elastic thickness and maximum fault segm ent length of both rifts are greater than those seen in many other act ive extensional regions on Earth, despite the high surface temperature s on Venus, We suggest that the southern East African and Venusian ela stic thicknesses and maximum fault segment lengths are due to stronger lithosphere. The rift systems differ in the maximum width of their ha lf 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 thic kness (compared to most other terrestrial extensional regions) means t hat wide half grabens can form without requiring the shear stresses ac ting 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 effect ive 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 d ifference is significant; Venusian faults must be stronger than those on Earth.