FAYETTEVILLE, Ark. — Measurements that track motion on the Earth’s surface in millimeters per year yield evidence that may help researchers better predict earthquake distribution and volcanic activity in the Caribbean, according to University of Arkansas researchers. The methods they use in the tropics also are applied to other regions of seismic importance like the New Madrid Seismic Zone.

The Caribbean research on seismic activity is reported in an upcoming issue of the journal Tectonophysics.

Researchers know that the Earth’s surface is broken into 12 major plates, with some minor plates. Until recently, researchers knew little about how the Caribbean plate moved with respect to other plates, said geosciences professor Pamela Jansma.

Using Global Positioning Satellite technology, Jansma and her colleagues have measured the annual movement of various Caribbean islands to determine the relative motion between the Caribbean and North American plates. The reported data come from a total of 11 sites spread among the islands.

"The edge of the Caribbean plate is in the process of being broken apart," she said. "These measurements have implications for where the active faults are."

The exact movements within the plates are complex, so the research team has GPS sites located at various positions among the islands to track plate motion. By doing this they have learned much about the movement of individual islands. The researchers also developed a better understanding of the movement of Puerto Rico relative to the North American and Caribbean plates.

"This work explains some of the processes going on there," Jansma said. "In general, earthquake hazard correlates with how fast plates move." The data indicate some movement from eastern Hispanola to the eastern Virgin Islands and also between the Dominican Republic and western Puerto Rico. Increased seismic activity north of the northern and easternmost Virgin Islands appears to bolster the GPS movement data.

While major earthquakes in the Caribbean occur sporadically, volcanic activity abounds on many of the islands. The Caribbean basin has 14 potentially active volcanoes, one of which demonstrated to the people who live on the islands that there is cause for continued concern.

The 1995 prolonged eruption on the island of Montserrat drove away more than half of the island’s 11,000 inhabitants, killed the tourism industry and buried the airport in a pyroclastic flow. Jansma and U of A researcher Glen Mattioli use GPS to study volcano deformation, which occurs more rapidly than plate movement.

"The volcano actually breathes," Jansma said. When erupting, the surface of the volcano subsides, but it begins to inflate when the eruption stops. GPS shows these subtle changes taking place even when everything appears to be quiet on the surface, and Mattioli and Jansma’s team demonstrated this during the Montserrat eruption.

"A lot of people thought the eruption was over, but the GPS showed it was inflating," Jansma said.

The researchers will soon apply similar satellite techniques to the New Madrid Seismic Zone, which has its own unique challenges, Jansma said. Movement in the area is much slower than in the Caribbean, which makes unraveling noise in the GPS signal critical and challenging. The researchers will use modeling techniques to remove that noise form the signal to get a clearer picture of displacement in the area.

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