A magnitude 6.5 earthquake struck Japan on Friday, causing widespread injuries and property damage. Then on Saturday evening, a magnitude 7.8 earthquake hit Ecuador on the other side of the Pacific, collapsing buildings and killing more than 350 people.
With two large earthquakes happening only days apart, it might look like they’re connected. But how earthquakes influence each other is rather complex, particularly over long distances.
Aftershocks
Large earthquakes are caused by the rupture of faults that are a few tens of kilometers long for magnitude 7, to more than 1,000 kilometers for magnitude 9 and above.
The local perturbations caused by the sudden shift of rock mass across a large rupture results in a cascade of smaller earthquakes, called aftershocks, at distances roughly equivalent to the length of initial fault rupture. Aftershock rates peak immediately following the mainshock and decay exponentially with time.
However, if nearby faults are locked and already stressed, more damaging earthquakes may be triggered in the short term. The 2004 Sumatra magnitude (Mw) 9.2 and 2005 Mw 8.6 Nias earthquakes are the best known examples of short-term “clustering” of very large quakes.
