Paleoseismology, seismic cycle and tectonic coupling of the Lesser Antilles subduction zone based on coral microatolls

Powerful earthquakes have rocked the Earth since time immemorial. Today, though, they pose an even greater threat than ever, as population growth has put many more people in harm’s way. Dr. Belle Philibosian is bringing much needed attention to the at-risk region around the islands of the Lesser Antilles. Here, the North and South American plates of Earth’s crust are sliding under the Caribbean plate, in the type of interaction (subduction) that produces the most severe earthquakes on the planet and accompanying tsunamis. To assess the risk, it is necessary to know the seismic track record of the region and, for this, she is looking back in time with the help of a surprising partner, marine coral. This is because a powerful quake can transform the topography, uplifting previously submerged areas above the ocean surface. The remains of coral colonies on dry land bear witness to such violent movements of the Earth, going back hundreds or even thousands of years.
Similarly, less extreme position changes are observed in coral microatolls – colonies that, on top, are exposed to air and have died, but continue to grow horizontally beneath the water’s surface. These are natural records of relative sea level change, which can reflect deformations of the Earth’s surface that occur as the two plates struggle to move past each other. Dr. Philibosian’s results show this currently happening in the Lesser Antilles, the strain building up until it is released in some future earthquake. Her conclusions so far are consistent with the idea that a major quake in 1843 occurred deep along the boundary between the two plates. From such information allowing her to characterize the Earth’s activity in this region, Belle aims to produce models capable of estimating the earthquake risk, as well as the location and size of coming quakes. The catastrophic consequences of such events, like those that occurred along similar plate boundaries in Japan and Sumatra in recent years, make the stakes of such research all too clear.