I have heard a lot of similar reports over the last several days. That noise is common
with these earthquakes. Almost sounds like some kind of underground explosion.
The other mysterious thing about these pairs of earthquakes is the question:
"Where are the smaller events". If this was typical rupture there ought to be
10 magnitude 3's for every magnitude 4-4.5, 100 of Ml 2-3. But the seismograms
show none of these. This is much more typical of explosions than ground
fracture.