CORVALLIS, Ore. (KOIN) — Big earthquakes appear to follow a brief episode of “shallow mantle creep” and “seismic swarms,” according to new research at Oregon State University.
The study was published Monday in Nature Geoscience and offers an explanation for the foreshocks obeserved prior to large quakes.
The findings, according to the study, are an important step toward understanding the relationship and intersections between aseismic slip and seimic slip. Aseismic slip — also known as a silent or slow slip — is a displacement along a fault that occurs without notable earthquake activity.
Researchers focused on the Blanco Transform Fault off the Oregon coast for the study. A transform fault is a plate boundary at which the motion is mainly horizontal.
Under the sea, transform faults connect offset mid-ocean “spreading centers,” which are places at seafloor ridges where new oceanic crust is formed through volcanic activity and gradually moves away from the ridge.
For the study, researchers deployed 55 seismometers on the ocean botton on and around the Blanco fault for a year.
From September 2012 to October 2013, the seismometer deployment resulted in the detection of more than 1,600 earthquakes at the Blanco Ridge that the study monitored.
According to the study, two distinct asperities along the ridge rupture about every 14 years with earthquakes in the magnituge 6 range.
At its southernmost point, the Blanco Transform Fault is about 100 miles from Cape Blanco — Oregon’s westermost location. The fault runs northwest to a point about 300 miles from Newport.
The Cascadia Subduction Zone lies between the Blanco fault and the coastline. The research also states that “the fault was the site of a magnitude 9 earthquake in 1700 and is building up stress where the Juan de Fuca Plate is sliding underneath the North American Plate.”
Some scientists predict that there’s a 40% chance of another magnitude 9 or bigger earthquake happening along the fault in the next 50 years.
“The Blanco fault is only 400 kilometers offshore,” Nabelek said. “A slip on Blanco could actually trigger a Cascadia Subduction slip; it would have to be a big one, but a big Blanco quake could trigger a subduction zone slip.”
The research goes on to explain the boundary between the crust and the next layer — the upper mantle — known as the Moho.
According to Kuna, the layers have different levels of seismic “coupling” — the ability of a fault to lock at asperities and accumulate stress.