Given the distances involved, we used a hyperbolic distance metric as opposed to the more commonly
employed planar Pythagorean formula. We obtained several singleton outliers (plus a pair at Salta)
that likely merit a careful analysis to determine if they really were caused by the initial 8.8 event
offshore of Maule Chile 2/27/2010 at 6:34. Date and time are UTC; estimated depth in kilometers.
We obtained one cluster of nine aftershocks in Ecuador; a second cluster of 13 aftershocks angling
NW-SE inland of Cajamarca; a third cluster of 13 aftershocks along the Peruvian coast near Callao;
a fourth cluster in the Atcama Desert between Arica and Antofagasta in Chile; a fifth cluster near
Salta in northwestern Argentina; and a huge sixth cluster between 30 and 40 degrees south along the
Chilean coast; a small seventh cluster of four aftershocks around the Chonos Archipelago and an
eighth cluster in the ocean at about 40 degrees south and 90 degrees west.
Of particular interest to us was not just that there were hundreds of aftershocks greater than 5.0,
which was impressive in itself, but that there were thirty-one 6.0 or greater events. We were not
completely surprised by the 6.9 at 8:01, but we were certainly not expecting another one on 3/11, not
to mention 6.7s on 3/11 and 3/16; a 6.6 on 3/5 and, probably the most interesting, a 6.5 on 5/24.
Mathematically, were this data representing something else like CPU usage on a computer, we would
be much more comfortable assigning the clusters of aftershocks to multiple events. After some
preliminary work associating aftershocks with known faults we cannot justify the pattern of
aftershocks as being caused by one major movement. We could scarcely argue that there was a huge
tear, but we are obliged to conclude that there were eventually multiple epicenters. This leaves us
with the task of determining what is an earthquake and what is an aftershock as well as finding some
physical model that explains the events. Of interest is that many geologists now suspect that the
Indian Ocean tsunami actually had two associated earthquakes. We are experimenting with a
multi-dimensional analysis we call tectonic tides - preliminary result suggest that Chile 2010 was
five associated earthquakes. One implication is that had these hypothetical events been closer in
space and time Chile might have been slammed by something greater than the already awful 8.8