麻豆淫院

Sometime between 1381 and 1391, an earthquake exceeding magnitude 8.0 rocked the northeastern Caribbean and sent a tsunami barreling toward the island of Anegada.

, depositing coral boulders hundreds of meters inland. The corals died but their skeletons remain. More than six centuries later, scientists are learning that these skeletons hold clues about tsunami history. showed the flooding likely resulted from a tsunami generated during a large earthquake in the nearby Puerto Rico Trench.

Now, in a paper recently in Geophysical Research Letters, researchers narrow the tsunami time frame to the last decades of the 14th century. The researchers expect this finding to support ongoing efforts to prepare for future Caribbean tsunamis.

"If you're designing a school or a hospital near the coast, you want to know whether there's a chance that a very big earthquake could occur, and you want to design that building to withstand it," said corresponding author Brian Atwater, a University of Washington affiliate professor of Earth and space sciences and research geologist with the United States Geological Survey.

Anegada is the northernmost of the British Virgin Islands, sitting just south of the Puerto Rico Trench, where the Caribbean and North American plates converge. Most of the islands are protected by a broad, shallow continental shelf. Waves lose energy as they roll across the expanse, decreasing the chances of a tsunami hitting Caribbean shores. Anegada is different鈥攖he seafloor slopes steeply toward the deep trench, making the island more hazard-prone.

Written records from the northeastern Caribbean go back five centuries, but none provide evidence for a tsunami from the Puerto Rico Trench. Geology allowed the researchers to evaluate tsunami history on a longer timescale.

Researchers began surveying the region after a massive earthquake and tsunami struck the Indian Ocean in 2004, killing more than a quarter of a million people.

The disaster surprised everyone, including researchers, prompting officials in the U.S. to on the Atlantic seaboard. Uri ten Brink, one of the project leads and a research geophysicist at Woods Hole Coastal and Marine Science Center, asked Atwater to check for signs of similar activity on Anegada. Atwater had spent years in Indonesia after the tsunami.

The evidence uncovered on Anegada drew various research teams to the island and produced a series of discoveries.

In the most recent study, led by Hali Kilbourne, an associate research professor at the University of Maryland Center for Environmental Science, the researchers present a time frame for the medieval tsunami based on how old the coral was when it died.

They calculated age by measuring two radioactive elements鈥攗ranium and thorium鈥攖hat decay at known rates. These measurements were made on samples from the inside of the coral skeletons, due to weathering and potential contamination. The researchers then added the number of annual growth bands between the dated sample and the exterior of the coral to estimate when the tsunami occurred.

"Corals have annual density bands, much like tree rings," Kilbourne said. "We were able to count how many years passed between the top density bands and the sections we used for dating."

Kilbourne can also gather valuable environmental data from the coral skeletons, which store information about temperature and salinity, and plans to continue studying the samples to better understand climate change over longer timescales.