I know I've done various demo plots of earthquakes in MapPoint on this website and my own, but in this case I think you're pushing the limits of MapPoint. The redraw is probably pretty slow as well, isn't it?
What you could do is to colour code the earthquakes according to their depths.
Another option might be to "bin" the data into small square areas, and store #number of earthquakes for each 'bin'. Then you could use my GridImp application to plot these. You would then have a coloured map with different colours representing different nos. of earthquakes in that area.
http://www.mapping-tools.com/gridimp/index.shtml for details.
Most of my examples actually use earthquake hazard data
Slightly off topic, what is the state of research in the Geysers? When I was with the USGS about 10 years ago, they were starting to do tomographic studies of the area. They were also mapping Vp/Vs ratios, and also correlating the earthquake swarms with fluid injection.
Richard