Slow Earthquakes May Predict Massive, Devastating Quakes

There may be a new way to predict earthquakes. Scientists have discovered that monitoring slow earthquakes may provide a basis for reliable prediction in areas where slow quakes trigger normal earthquakes.

Normal stick slip earthquakes typically move at a rate of three to 33 feet per second. Slow earthquakes in contrast, move at rates of about .004 inches per second. In fact, they can take months or even longer to rupture. These slow earthquakes often occur near traditional earthquake zones and may precipitate potentially devastating earthquakes. Needless to say, it's crucial to better understand these slow earthquakes to potentially predict larger ones.

"We currently don't have any way to remotely monitor when land faults are about to move," said Chris Marone, one of the researchers, in a news release. "This has the potential to change the game for earthquake monitoring and prediction, because if it is right and you can make the right predictions, it could be big."

In order to examine these earthquakes a bit more closely, the researchers looked at serpentine, a common mineral often found in slow earthquake areas. The scientists applied shear stress to rock samples so that the samples exhibited slow stick slip movement. After performing these tests several times, they found that slow fault zones undergo a transition from a state that supports slow velocity below about .0004 inches per second to one that essentially stops movement above that speed.

So what causes this unusual pattern of movement? It's likely that friction contact strength goes down as velocity goes up, but only for a small velocity range. Once the speed increases enough, the friction contact area becomes saturated. This limits the speed of slow earthquakes.

The researchers also looked at the primary elastic waves and secondary shear waves produced by these experiments. They found data that was similar to what they could see in the field and what seismographs could record.

Currently, there are not sufficient measuring devices adjacent to known fault lines to make any type of prediction from the precursor signature of the movement of the elastic waves. However, in the future proper instruments could potentially lead to some kind of prediction of more massive quakes.

The findings are published in the journal Science.