Coral Reefs and Earthquake History: Tale is There

In a clear sign that all is connected, particularly to our terrestrial coral reefs, researchers who were studying uplifted coral along the eastern coast of one of the western Solomon Islands (Ranongga) found evidence of six earthquakes in the region in the past 3,000 years. This was a significant learning, because the western Solomon Islands were a region thought to be free of large earthquakes until an 8.1 magnitude quake hit in 2007, according to a release.

The team, led by researchers at The University of Texas Austin, published their findings online in Nature Communications this week. Their findings suggest that future large earthquakes will occur, but predicting their timing is difficult because the area's tectonic plates interface in a complex arrangement, the release said.

The coral not only shows a record of earthquakes in the last 3,000 years, but also provides insight into the relationship between earthquakes and more gradual geological processes--including techtonic plate convergence and island building through uplift, the release said.

"We're using corals to bridge this gap between earthquakes and long-term deformation, how the land evolves," said lead researcher Kaustubh Thirumalai, a doctoral student at the University of Texas Institute for Geophysics (UTIG), a research unit within the Jackson School of Geosciences, according to Eurekalert.

Here's how evidence can be left in corals: When an earthquake hits, land at its epicenter can be lifted several feet. In an area of shallow-water seafloor, such as around the islands, corals can be lifted out of the water. Air kills the polyps that form the coral, leaving behind their network of rock-like skeletons, according to the release.

The time of the earthquake is recorded, as well as an estimate of how strong it was. Through a chemical process similar to carbon dating, scientists can learn the coral's time of death. The amount of uplift in the land can give clues as to the quake's strength, the release said.

"If we have multiple corals going back in time, and we can date them very precisely, we can go from one earthquake, to many earthquakes, to thousands of years of deformation of the land," Thirumalai said, according to Eurekalert.

The area earthquakes result from plate tectonic motion near the island; the Pacific Plate starts to subduct beneath the Australian Plate, about two miles from shore. One theory of island building is that earthquake uplifts are a main driver in land creation, the release said.

There's more to learn, however. The corals' earthquake record was not enough to account for the measured rate of tectonic convergence. Consequently, other geological processes likely play an important role in the islands' tectonic plate movement and uplift, the release said. But this study has shown uplifted coral are important geological tools.

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