In today’s Academic Minute, Cynthia Ebinger of the University of Rochester explains the connection between earthquakes, volcanism, and the changing thickness of the Earth’s tectonic plates.
Cynthia Ebinger is a Professor of Geophysics at the University of Rochester where her research is focused on active and ancient plate boundary processes, with a primary interest in the process of continental rifting leading to rupture and the formation of new oceanic lithosphere. She is currently studying rift systems in Ethiopia, Tanzania, the Gulf of Aden, and southern Australia.
Dr. Cynthia Ebinger – Understanding Volcanic Plumbing
Earth's continents are reshaped continually by tectonic movements. The most dramatic of these is the rupture of 120 km-thick plates after millions of years of stretching and heating in continental rift zones. New ocean basins are formed as molten rock rises to the surface between the separating plates, then cools and sinks below sea level. North America and Africa separated through this process more than 180 million years ago, providing tantalizing clues, but no direct observations.
Scientists are able to make direct measurements of changes in plate boundaries after short, sharp episodes of intense activity. And that was the case in one region of special interest: the Afar Depression of Ethiopia in East Africa. Earthquakes and volcanic eruptions rocked the region in September 2005, resulting in a short-lived period of plate-thinning. Further activity over the following six years led to new insights into continental rifting processes.
Seismometers we installed in the remote Afar Depression have detected seismic waves generated by earthquakes from plate boundaries around the globe. As part of a new study, Kate Rychert of Southampton University used these data to create images of the continental plate from the bottom up to better understand the plate-thinning process. The African plate thins from more than 100 km to about 20 km beneath the Afar Depression, with a sharp transition between the thinned and un-thinned plate. Thus, all or most of the continental plate has been stripped away by convection currents in Earth's deep mantle, a process more efficient than previously thought.
Our findings not only inform earthquake and volcanic hazard mitigation in east Africa, but provide vital constraints on the evolution of the east coast of North America.