Cascadia initiative gathers information on Northwest Pacific seismic risks

The project “offers a unique opportunity to image the seismic structures associated with an entire plate, including its spreading center and subduction zone, within an easily accessible part of the continental and offshore United States,” said University of Massachusetts Amherst researcher Haiying Gao, a guest editor of the SRL focus section.

“I don’t think we can predict the time or location of the next megathrust earthquake in the CSZ based on the current research progress,” Gao cautioned. “Nevertheless, the Cascadia Initiative significantly contributes to a better understanding of the structure of the downgoing oceanic plates and thus to the assessment and mitigation of potential seismic and tsunamic hazards.”

For instance, a paper by New Mexico Tech researchers Emily Morton and Susan Bilek describes ninety-six small new earthquakes occurring in 2011 and 2012 that were detected with the help of the Initiative’s ocean floor seismometers. These earthquakes occurred in the shallow, offshore “locked” part of the CSZ, where the fault is stuck in place, and had not been observed by land-based instruments. Detecting and locating these small seismic events can help researchers understand how strain on the megathrust fault may be changing, and to help predict how the megathrust might behave during a large rupture.

The seismic data collected by the Initiative has also helped Gao and her colleague Yang Shen at the University of Rhode Island, along with another study by Columbia University scientist Helen Janiszewski and Cornell University researcher Geoffrey Abers, to compile a picture of the CSZ structure that points to new places where the crushing pressure of subduction is squeezing water from and transforming rock at the trench where the Juan de Fuca plate is bending under the North American plate. The newly deployed seafloor seismometers, said Gao, have offered an unprecedented look at how released fluid can affect the fault’s strength and behavior at the offshore trench.

Offshore instruments are important tools for observing and detecting tsunami risks in the region, according to a paper by Anne Sheehan of the University of Colorado Boulder and colleagues. They compared readings from several types of seafloor pressure gauges to study the tsunami caused by the 2012 Haida Gwaii earthquake, to evaluate how well the gauges could detect the timing and size of a tsunami.

Other papers in the issue examine how deep sea sediments may affect seismic wave readings, and evaluate how the Cascadia Initiative’s data collection from ocean bottom seismometers has improved over the first three years of the study.