By Maya Wei-Haas
In the predawn hours of January 7, residents across the island of Puerto Rico were jolted awake as a magnitude 6.4 earthquake rocked the region. While earthquakes in Puerto Rico are not unexpected, this temblor is just the largest in a series of quakes that has rattled the island for more than a week—and odds are that the shaking is not over yet.
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The events have wreaked havoc in a community still recovering from devastation in the wake of hurricanes Maria and Irma. The latest pair of large temblors collapsed homes, knocked out power in some regions, triggered landslides, and toppled the natural rock arch Punta Ventana—a popular landmark that was long a draw for tourists. At least one death has been reported so far.
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Under the island’s northern coast, the North American plate plunges under the Caribbean plate in a subduction zone. At the same time, a section of the Caribbean also seems to subduct south of the island at the Muertos trough, squeezing Puerto Rico in between them, according to the USGS. The result is earthquakes, and lots of them.
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The island is particularly susceptible to what’s known as earthquake swarms, or series of events that are roughly the same magnitude, explains Elizabeth Vanacore, a seismologist with the Puerto Rico Seismic Network (PRSN) at the University of Puerto Rico at Mayagüez. Why, though, is an open scientific question, she says.
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