The scale on this is eight miles on a side, and the diagram is courtesy of a discussion board member called Shirakawa. This represents the magnitude, depth and location of the earthquakes in this series of quakes beneath the North end of Yellowstone Lake.
A correction of an earlier comment on hydrothermal explosions : "an explosion 13,800 years ago left a 5 kilometer diameter crater at Mary Bay on the edge of Yellowstone Lake (located in the center of the caldera)." --FEMA Region VIII statement issued today.
Updated Map and listing of quakes at Yellowstone this week (incomplete as there are so many quakes that seismologist review is taking up to a day): Recent Yellowstone Quakes
The swarm has reintensified today after a slight drop in activity yesterday. It is interesting to note that the quakes continue to occur in the area of Yellowstone Lake beneath the dome on the lake's floor, and in the vicinity of most of the hydrothermal explosions on record. Like most people watching this interesting swarm, I'd love to hear from the U of U director, even if they aren't clear about what the quakes mean, to get an idea of what they are thinking. Still, I guess they cannot speculate too much, as spooking people would be a bad thing to do. So, we wait, watch and will see...