Formation of Beta Regio, Venus: Results from measuring strain

Beta Regio is an area of rifting and volcanism on Venus, constituting a top ographic rise. A shield volcano, Theia Mons, lies near the center of the re gion and is surrounded by several radially oriented rifts. We use Magellan altimetry, gravity, and synthetic aperture radar data of the area to constr ain some subsurface parameters. First, we derive hoop strain. Using altimet ry data and a fault dip angle derived from the split crater Somerville, we determine the extension in the rifts surrounding Beta Regio. We then derive the hoop strain accommodated by the rifts from the extension in these rift s. Except near Theia Mons, the hoop strain follows the shape expected from a mantle upwelling. The difference near the volcano, we believe, is due to volcanic infilling. We then model three observable quantities, the newly de rived strain along with gravity and uplift, using two separate modeling tec hniques, one for the strain and uplift and another for the gravity. The mod el results show that the data are consistent with the view that a relativel y low density contrast region now exists below Beta and has caused the upli ft and rifting in the region.