By tracking swarms of very small earthquakes, seismologists are getting a new picture of the complex region where the San Andreas fault meets the Cascadia subduction zone, an area that could give rise to devastating major earthquakes.

Chijun Sun, an assistant professor of earth and planetary sciences at the College of Letters and Science, recently returned to land after a months-long trip aboard the Chikyu, a deep-sea scientific vessel investigating the seafloor following a massive 2011 earthquake and tsunami.

Magali Billen, a professor in the Department of Earth and Planetary Sciences, seeks to unravel the forces that drive plate tectonics from hundreds of kilometers beneath the Earth’s surface. Specifically, she’s interested in subduction zones — areas where two tectonic plates collide, causing one to dive back down into the Earth’s mantle.