[JimSEA]

The last eruption at Yellowstone was 70,000 years ago and was mafic, basaltic without the explosive nature of the earlier super eruptions. The magma chamber is huge and when it expands, the earth moves. If something was moving on up, you’d expect a flurry of earthquakes in the hundreds per day. A 5.1 mag quake is certainly within the normal expectations for this hot spot. As for the LA quake, it has no relationship to Yellowstone and little relation to this horrible 8.2 quake in Chili other than they are both on plate margins. However, Chile is on a subduction zone and LA is related to a strike slip fault though the specific fault may well be another type. I don’t know.

[PennsylvaniaMom]

Very well said. The earth is ALWAYS active seismically. I have been fascinated by EQs (and geology) since I was a (nerdy) teen. One thing that I had read recently is that gas monitoring stations in YS had detected (I think back in February) high levels of helium gas. This peaked my amateur curiosity in terms of increased seismic activity (the 4.8) but also the anecdotal occurrences (EQ “lights” are they gas generated in the period before a quake?) Again, I’m an amateur who reads about this.

Now Chile. Other than Japan’s usual swarms prior to the 9.2 (I think it was a 6.1 in the days that was originally considered “the” quake...and then noted as a foreshock) I cannot recall a “swarm” that (Chile has been having moderate quakes for weeks) that were truly foreshocks before a “big” one. Last I checked, there was a 6.2 aftershock a few hrs ago.

[tsomer]

the last eruption at Yellowstone was 70,000 years ago and was mafic, basaltic without the explosive nature of the earlier super eruptions.

Hi JimSea.

I read the article familyop linked. The graphic shows a core of basaltic magma--the kind that you find in Hawaii and, as I understand it, flows rather than explodes as Mt. St. Helens. But that basaltic magma has what they call a granitic cap-- and I wonder if that's cause for concern.

Of course there are different kinds of granite--mafic and felsic (sp?), but I don't know if we have a scenario like Mt St Helens, where the lighter and stiffer granitic cap blew and spewed so much ash into the air. Could that happen at Yellowstone?

Thanks.