Scientists involved in groundbreaking new research at Oregon State University have determined that major earthquakes are often preceded by “silent slips” and have finally discovered why foreshocks are common indicators of large and deadly earthquakes.
According to Oregon Live, major earthquakes normally follow “shallow mantle creep” and “seismic swarms,” and researchers are much clearer in their understanding now of the “silent slip,” which is what happens when different sections of the Earth’s crust can be observed shifting along the fault line. However, when this occurs, no seismic activity is ever detected, which has been confusing to researchers in the past.
But while this slip may be silent, it has profound implications for future events, as Oregon State University graduate student Vaclav Kuna learned after studying 55 seismometers which had been placed strategically along the Blanco Transform Fault and left there for a year. This, according to Kuna, was the perfect location for these seismometers as it is such a seismically active fault.
“It’s a very seismically active fault that generates significant earthquakes at higher rates than the majority of faults on land, making it ideal for studying the process of earthquake generation.”
As Kuna explained, after studying the seismometers, it was determined that these slow slips frequently triggered large earthquakes.
“Slow slip directly triggers seismic slip – we can see that. The findings are very interesting and may have some broader implications for understanding how these kinds of faults and maybe other kinds of faults work.”
— The Oregonian (@Oregonian) January 21, 2019
To learn more about faults, Kuna and fellow researchers examined what was below the Earth’s crust by studying the Moho, or upper mantle area. Co-author John Nabelek noted that when silent slips occur at this depth, this is what is believed to cause larger earthquakes.
“We see slow, seismic slips that occur at depth in the fault beneath the Moho and load the shallower part of fault. We can see a relationship between mantle slip and crust slip. The slip at depth most likely triggers the big earthquakes. The big ones are preceded by foreshocks associated with creep.”
Because of the close proximity of the Blanco fault to the Cascadia Subduction Zone, Nabelek suggested that “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 new research which details how silent slips often precede large earthquakes has been published in Nature Geoscience.