| I investigated rifts in multiple stages of their formation, from the failed Mid-Continent Rift (MCR), to the active Red Sea Rift. Each rifting stage presents its own challenges but by studying each stage individually I have gained insight into the rifting process.;The MCR, an ancient failed rift, stretches through most of the Midwestern U.S. It is primarily identified by gravity and magnetic anomalies. I model gravity data to explore the variation in magma volumes along the MCR. The variations are consistent with a microplate model, which explains the difference in gravity signature for the two rift arms.;The gravity models over the MCR give key insights into the `local' formation tectonics, I also studied the regional tectonics to further understand how a massive rift failed to break the continent. I use Geologic, paleomagnetic, and geophysical evidence to formulate a new model the evolution of the MCR. This model showed that the MCR formed as part of continental breakup and fails once breakup is complete, removing the stresses needed to continue rifting.;Next I investigated the seismicity of a failed rift and a passive margin. The New Madrid Seismic Zone (NMSZ), which lies over the failed Reelfoot Rift, has been seismically active since a series of three ∼M7 earthquakes in 1811-1812. I tested suggestions that this sequence of earthquakes transferred stress to the nearby, geologically similar, Wabash Valley. I quantified the difference in seismicity between regions and show that it instead probably reflects long duration aftershocks in the NMSZ. Following up this study, I modeled the seismicity of the east coast of North America and found the largest known earthquakes there likely reflect the length of the available earthquake catalog rather than the largest possible events.;I examined the Red Sea Rift, an actively spreading region, building on a tomographic model by Sung-Joon Chang and coauthors that identifies a low velocity channel underlying recent volcanism in Arabia. Integrating this and other geologic and geophysical evidence I purpose a scenario in which the northern Red Sea is abandoned and the rift jumps inward into Arabia, `re-rifting' the continent. |
