Month later, Alaska STILL shaking with aftershocks from 7.0 quake
On Friday, November 30, a magnitude 7.0 earthquake struck Anchorage, Alaska. The initial jarring was destructive – and now, more than a month later, daily jolts continue to leave residents shaken.
Since the main shaking, about 350 aftershocks of magnitude 3 or greater have been registered on seismometers. Some – including the five 5.0 or worse quakes – have been large enough to cause additional damage. Though the aftershocks have slowly been winding down, the magnitude 5.0 tremor on Jan. 1 and magnitude 4.2 on Wednesday show that Alaskans are far from out of the woods yet.
That begs the question – how long will the earthquakes continue? We can turn to a little bit of seismology for the answer.
After a quake, swarms of aftershocks persist for weeks or even months. The bigger the main earthquake, the stronger and more frequent the aftershocks. The occurrence of aftershocks drops off exponentially as time progresses per a relationship known as Omori’s Law . By fitting an equation to the number of observed aftershocks, we can extrapolate trends into the future.
Likewise, it’s possible to forecast the intensity of said aftershocks. That comes through the Gutenberg-Richter equation . It breaks down the percentage of aftershocks that reach different levels of strength. It’s like a pyramid – as you climb in magnitude, each tier gets more narrow. It’s a logarithmic relationship.