Well no need to wonder anymore—Questionland has the answers! We have a panel of earthquake experts standing by, including Robin Friedman, Director of King County Emergency Management, Paul Bodin, a UW seismologist and Associate Pofessor at the Department of Earth and Space Sciences, and Bruce Schoonmaker, an earthquake preparation specialist.
And to answer that question about Mt. Rainier... Bodin says:
This is really a great question. And the proof is that some scientists say earthquakes can affect volcanic eruptions and some say no way . If we can't agree, then I guess I really have no right to give you a "yes" or "no" answer. Ok, enough of a disclaimer; now I can tell you what I think...
There is some statistical evidence that there were more eruptions after large Chilean earthquakes in 1906 and 1960. But the mechanism by which this "triggering" might happen isn't clear. There's also lots of anecdotal evidence of particular eruptions following certain earthquakes. But such stories suggesting correlation are not entirely convincing, nor do they demand causality . However, it sure seems plausible that shaking from seismic waves can jostles magma and make it move around—and rise toward the surface if it is so inclined. But it takes magma time to work it's way to the surface. So the difficulty in observing earthquake-triggered eruptions, then (according to me) is that there are likely to be variable delays between the triggering earthquake and the ensuing eruption. Drawing the connection between any given earthquake and some ensuing eruption is uncertain.
I also think that as our capabilities to monitor both ground motion from earthquakes and the deformational processes that precede eruptions, we will be able to x-ray this whole process and answer this question concretely.