2017 Earthquake Sequence In Central Chile
Seismic swarm: There was a clear sequence of seismic events that led up to last night's M6.9 earthquake.
The first event of this seismic sequence occurred on 22 April with a magnitude 4.9 quake.
The following day, there were many more small and moderate sized events, including a M5.9 quake.
We call this sequence a seismic swarm because it contained many similar sized events occurring in the same location and within a short time of each other.
There is some indication a number of these events may have occurred on splay faults that branch from the main subduction fault.
Good article. Get full article in the twitter link below.

For some reason it won't let me post the link to this article, so I am posting it through Stephen Hick's (author of the article) twitter link below.
*I've just written a blog post on the seismic sequence offshore of Valparaiso, central Chile: what we know so far.*
[link to twitter.com (secure)]

Chile foreshock & main shake location diagram from the article above (Note: 7.1 should read as 6.9, due to it being downgraded)
IMAGE ( [link to i.imgur.com] )