Radially fractured centers (RFCs) on Venus are distinctive, ~100 km long radiating systems of graben, fissures, and fractures arranged around a central topographic high. We use cycle 1 and cycle 3 Magellan images to determine the depths and wall dip angles of several large radial graben, using two different methods, at four RFCs: Becuma Mons, Didilia Corona, H'uraru Corona, and Pavlova Corona. We record graben depths of 0.3--0.9 km and mean wall dip angles of about 36¿, which we interpret as a primary talus slope rather than a fault plane. Using the calculated depths and a more realistic fault dip of 60¿, we find extension of between 0.5 and 1 km on graben between about 5 and 10 km wide. We use this extension to estimate the hoop strain at each RFC. Maximum measured strains on the flanks are typically between ~1 and 4% and may be up to 7% toward the center. We conclude that this strain is too large to be explained by current plume-related uplift models and also by magma chamber inflation. We conclude that dikes are probably responsible for the majority of the strain at the large radial graben.