precursory

"There are some cases where there are dramatic and very distinctive precursory seismic signals that precede a catastrophic landslide, sometimes by as much as days," Highman noted.

Scientists suspected that the next eruption would follow a similar precursory pattern to the past three: lots of earthquakes as magma breaks through rock on its way to shallow parts of the crust, accompanied by the ground changing shape to accommodate the shifting magma.

“It doesn’t give you a precursory, predictive ability because it’s a statement of how you’ve summed it rather than what’s going on at a particular earthquake,” she adds.

Interestingly, a larger fraction of those very biggest earthquakes seem to have exhibited some precursory events, either in the form of a series of foreshocks detected by seismometers or sped-up movements of the nearby Earth’s crust detected by GPS stations, called “slow slip events” by earthquake scientists.

These observations suggest perhaps there really are precursory signals for at least some huge quakes.