Just days after eastern Connecticut experienced a series of minor earthquakes, Yale University announced Yale-led research may have solved the mystery of why tectonic plates beneath the Earth\u2019s surface move abruptly. A new study published Monday, Jan. 19 in the journal Proceedings of the National Academy of Sciences says the answer comes down to two things: thick crustal plugs and weakened mineral grains. Those effects, acting together, may explain a range of relatively speedy moves among tectonic plates around the world, from Hawaii to East Timor. In this case, however, \u201cspeedy\u201d still means a million years or longer. \u201cOur planet is probably most distinctly marked by the fact that it has plate tectonics,\u201d Yale geophysicist David Bercovici, lead author of the research, said in a press release. \u201cOur work here looks at the evolution of plate tectonics. How and why do plates change directions over time?\u201d Traditionally, scientists believed that all tectonic plates are pulled when the colder, top boundary layer of the Earth\u2019s rocky surface becomes heavy and sinks slowly into the deeper mantle. This process is known as subduction and typically occurs at the rate of a few centimeters per year. That process does not account for sudden plate shifts because the top layers \u2014 or slabs \u2014 are too cold and stiff to detach. According to the Yale study, there are additional factors at work. Thick crust from continents or oceanic plateaux is swept into the subduction zone, plugging it up and prompting a slab to break off. The detachment process is then accelerated when mineral grains start to shrink, causing the slab to weaken rapidly. The result is tectonic plates that abruptly shift horizontally, or continents suddenly bobbing up. \u201cUnderstanding this helps us understand how the tectonic plates change through the Earth\u2019s history,\u201d Mr. Bercovici said. \u201cIt adds to our knowledge of the evolution of our planet, including its climate and biosphere.\u201d The study\u2019s co-authors are Gerald Schubert of the University of California-Los Angeles and Yanick Ricard of the Universit\u00e9 de Lyon in France.