The idea of triggering of small earthquakes within 2,000-3,000 km of large earthquake
is now generally accepted by geoscientists. What many do not realize is that
the amplitude of seismic waves does not reduce monotonically with distance. There
distances from the source where the amplitude of seismic waves is very high (called
nodes) others where it is low. This variation in amplitude is caused by reflection and
refraction off the internal boundaries of the earth and by geometric focussing.
For example the calculated amplitude of surface waves near the antipode of an
earthquake (180 degrees away), is very nearly the same as the amplitude 500 km
away. If we can accept the idea that small earthquakes can be triggered at 500
km from a large source, why then, is it difficult to say that the same triggering
mechanisms can exist at long distances where the ground motion is similar.
Anyway, even if this is idle speculation, there is no better place for this kind
of speculation than on this board. I hope that we all understand that the field
of earthquake prediction is one of the few places left where speculation may actually
lead to results (since none of the current theories seem to be leading anywhere
except in circles - at least we can say they haven't been very successful at predicting
earthquakes.) So I welcome harmless quantum leaps - bring them on if you have
them.