Taylor and colleagues describe their work in the March 30 online issue of the journal Nature Geoscience.
Emile Okal is a geophysicist at Northwestern University in Chicago who was not involved in the study. He agrees with Taylor's conclusion.
"Indeed, what was considered to be a barrier was jumped," Okal said.
But he doesn't see this as a surprising find. Two decades ago researchers who reconstructed a 1932 earthquake in Mexico reached a similar conclusion.
"Ever since, we've looked at these triple junctions as vulnerable. We know that these are barriers that can be jumped," he said.
Lead author Taylor agrees that the Solomon Island's earthquake probably wasn't the only one of its kind.
Offshore from Washington, Oregon, and Northern California, the Cascadia subduction zone is divided into three major segments and several minor ones.
Geological evidence indicates that all of these segments had major earthquakes about 300 years ago.
"[The] paleoseismology doesn't prove it was a single earthquake," Taylor said. "It just proves that they all ruptured at about the same time."
But in 1700 Japan was hit by a tsunami that was probably caused by an earthquake in the Cascadia zone.
"Given the size of the tsunami, people infer that all of those segments ruptured at once," Taylor said.
"So we should be aware of the possibility that a lot of these segments will gang up on us at once and all break."
Such an event could cause a much more devastating earthquake than many researchers had thought possible in the Cascadia zone.
Young and Shallow
By contrast, the same study backed up theories about how deep earthquakes should be within the Australia-Woodlark subduction zone.
The location of the elevated reefs indicated that the 2007 quake was extremely shallow, Taylor said, involving only sections of the fault from the surface to a depth of 9 miles (15 kilometers).
This matches theories that relatively young, warm subducting plates can form shallow quakes.
"The younger the down-going plate, the shallower the rupture zone should be," he said.
That's because younger plates have not yet fully cooled from the lava that formed them.
Warmth means that the plates' constituents, most notably clay minerals, can get stuck as they move, building up tension that causes earthquakes.
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