The current earthquake swarm of January 1999 is in an area with frequent historical earthquake activity. Here we show the seismicity of the region throughout the 1980s and 1990s.
The colored "beach ball" shows a standard representation of the
fault plane solution for the magnitude 3.2 earthquake on January 11,
1999, 02:04 PST derived from recorded
P-wave motions on seismograms. It indicates that the earthquake
occurred at a depth of 7 kilometers on a normal fault
that trends NW-SE through Mount Hood. The figure shows
previous earthquake activity on the same fault as well as other
earthquakes.