How do we know that this was the top end of the quake? I was once in the midst of an earthquake swarm not far from a volcanic mountain. The geologists called and were very interested in what was going on. I asked, "How do you know if this is a swarm building up to a big blow or quake or just a swarm cooling down from one already passed?"
They said. "We don't know. We can only tell by looking back after the biggest event."
If a swarm predates a big blow (like Mt. St. Helens did and like the various swarms around the world), then you can't tell if a swarm of varying sizes (say 3.7, 4.2, 3.6, 4.0, 3.9, 4.5, 4.6) or as in this instance 7.6, 4.9, 5.1, 5.0, 5.0, 5.0, 5.1 is getting bigger or getting smaller. In other words, the 7.6 might not have been the top end.
Here is a book which indicates that accurate forecasts can be made in the scientific community. Volcano Eruption Great Earthquakes Advance Warning Techniques Book
