Yesterday, a mild (2.5) earthquake was recorded in Massachusetts. According to a local news story, there was also a 1.8 quake in the area earlier this month. According to the story, “Officials said that [earlier] quake was a late aftershock of an earthquake from 1727 in Newburyport.”
Wow! An earthquake can produce an aftershock two hundred and eighty years later?
How do seismologists distinguish between an aftershock and a new, unrelated earthquake in the same area?
Someone goofed. Either someone misspoke, was misquoted or there was a misprint.
I do not know precisely how long after an earthquake am aftershock may occur but there is actually an equation called Omori’s Law that follows this and it has a time component.
There is no way that was an aftershock of a 280 year old earthquake.
Okay, based on this story, I’ve identified the unnamed “official”. The reporter says,
Ebel identifies the quakes of 1999 as aftershocks and implies that these are as well, at least according to the reporter. I can easily imagine, though, that he said the recent quakes are connected (having roughly the same epicenter) and the reporter jumped to the conclusion “aftershocks.”