They also occur with astonishing regularity.
Known as Episodic Tremor and Slip (ETS) in scientific parlance, the earthquakes amble along the Cascadia fault roughly every 14 months in near-predictable cycles â€" and in maddening contrast to their destructive counterparts, which are notoriously difficult to forecast.
Many scientists think the slow quakes deep inside the fault could be building up stress in Cascadia’s shallower regions, essentially prepping the fault for a large earthquake. However, the location of the slow earthquakes is important to this theory. “It depends on where it’s occurring,” Trehu said.
Answering that question will send scientists well on their way toward solving what amounts to a high-stakes seismic algebra problem.
Solve for x On one side of the equation is the fault’s overall movement over time. Scientists have a basic understanding of that figure. “We know what the large-scale motion should be,” Trehu said.
To complete the equation, scientists have to hunt down all the sources of that movement. Regular earthquakes are one source, and a source that scientists can measure with some degree of precision â€" even the tiniest earthquakes broadcast their activities loudly enough for instruments to hear them.
However, slow-motion earthquakes â€" ETS â€" are sneaky. Instruments must be close by to pick up on them.
The newly installed ocean seismometers are designed to listen for slow-motion quakes along the seaward, shallower regions of the fault. if they are indeed occurring there, it could be that the fault isn’t primed for disaster â€" at least not now.
“If the whole fault is slipping slowly, then it’s not locked,” and thus not storing up energy for a large earthquake, Trehu said.
Barclay said he’s looking forward to getting his hands on the data a year from now, hoping they’ll indicate whether the slow-motion earthquakes are occurring. “It’s exciting for me because it’s episodic â€" and up to now our idea of subduction zones is that things happen at random,” he said.
However, Trehu said, the project has even grander ambitions than sniffing out hard-to-detect quakes and imaging the subduction zone. Ultimately, the goal is to understand how the entire system works â€" how and why earthquakes happen at all.
“It’s poorly understood what factors control whether the rupture continues to propagate, what factors stop the rupture,” she said, “and it’s those factors that determine how big the earthquake is.”
Scientists from more than six universities and institutions around the country have banded together for the Cascadia project, a years-long undertaking that is funded, in part, by the American Recovery and Reinvestment Act.
The researchers will make the data freely available to anyone who wishes to use it.
In the meantime, Trehu and Atwater said, people who live within the reach of the Cascadia subduction zone should be aware of the fault’s potential. [Related: 7 most Dangerous Places on Earth ]
“People should definitely think about the fact that a large earthquake is probable, eventually,” Trehu said. “A tsunami that’s generated in Cascadia will only take tens of minutes to get to the coast. so if you’re at the beach and you feel an earthquake, the best thing to do is get to higher ground as fast as you can.”
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Reach Andrea Mustain at . Follow her on Twitter @AndreaMustain.
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