Experts plumb depths of quake-causing cracks on the Pacific sea floor
New research focused off the West Coast of North America is giving seismologists a better understanding of what one scientist describes as “the single greatest geophysical hazard to the continental United States.”
Zach Eilon, a geophysicist at the University of California Santa Barbara, has developed a new method that uses an array of scientific instruments spread across the sea floor to measure shock waves that travel through the planet’s crust.
The waves, which are called attenuation, provide clues about rock temperatures deep below the surface of the Earth, which is important for understanding the friction that builds up between tectonic plates as they rub against one another, he said. The amount of friction affects the size of an earthquake created when the plates give way, as well as the destructiveness of an accompanying tsunami.
Eilon’s research targets the Juan de Fuca plate, which runs several hundred kilometres off the coast between southern B.C. and Northern California, and is the youngest and smallest of the planet’s 13 major tectonic plates.
The collision zone in this region has the potential to generate massive quakes and destructive tsunamis, which occur when the plates overcome friction and slip past one another, quickly displacing huge amounts of water.
His data suggests the interior of the Juan de Fuca plate is cooler than previously believed, meaning the edge that is being pushed westward below the North American plate is able to bring with it more water. The water acts as a lubricant and increases the likelihood of the slipping that leads to a quake.
Geoff Abers, an Earth-sciences professor at Cornell University who co-authored the paper with Eilon, said improvements in seafloor technology and the sheer number of sensors that were deployed make this project the first time researchers have been able to study an entire tectonic plate in the ocean.
“We’re not directly looking at the big-earthquake cycle, but we’re looking at the broader, theoretical framework for how the Earth works and getting a much better handle on that,” Abers said.
“The relevance is it helps us calibrate a lot of the models that we have when we try to understand things like how fast plates are moving, how they interact and what the temperature conditions are on the faults that are going to make the big earthquakes.”
The work, which was published in the journal Science Advances, will help with more accurate seismic modelling and improves hazard assessment and emergency preparedness.
West Coast residents have long been warned about the threat of a large quake, which scientists have been forecasting for decades.
The study’s findings go beyond earthquakes, offering insight into other geological phenomena, Eilon said.
“Because we think that this particular phenomenon is strongly related to temperature and to molten rock beneath the Earth, this is a technique that can be applied to volcanoes to get a better sense of their plumbing system,” he said.
“At the moment, we’re sort of blind to a really large portion of the Earth’s surface. And the better we get at instrumenting and understanding the oceans and the ocean floor, the more we’ll understand about the whole planet.”
The next step is to take the project north and use the new technique and ocean-bottom seismometers to explore the Aleutian region off the coast of Alaska, Eilon said.