Mikey, can you explain those maps?
Julles: The USGS monitors quake activity pretty much in real time on their site. The Pacific Plate makes contact with the North American Plate where California is located and thus the area is quite active with earthquakes. Small earthquakes occur every day and most are much too small for people to even notice.
The size or magnitude of the earthquake is represented by the various colored squares. On the graph you see the sizes 7 through 1. The Baja quake was initially reported as a 6.9 quake and then adjusted to a 7.2.
This particular earthquake was a rolling earthquake here, some 200 miles away from the epicenter. Rolling earthquakes are not terrifying to most people as they tend to start out gentle, not the sudden violent jolt of other kinds of earthquakes. Thus you had people acting calmly at the swimming pool. However, notice they were outside, not inside as even during rolling earthquakes many people tend to move outside. The feeling of a rolling earthquake is like standing on a pitching boat. In fact many people, including the fetching Mrs. Mikey, reported becoming nauseaous. This quake was very long in duration, the longest I ever experienced and that also explains why many people reported intitial symptoms of being sea-sick. I usually don't notice nearby earthquakes that register below 4.0. If I'm active duriing a 4.0 earthquake I may not notice it. Any nearby earthquake registering 5.0 will definately get my attention. An earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0.
There are so many earthquakes here that their graph only shows the earthquakes that have occurred within the last week. Red means the quake occurred within the last hour. Blue means the quake occurred sometime within the last day. Yellow means the quake occurred within the last week.
If you go to the USGS site and click on the earthquakes it will give you specific information about that particular earthquake. As you can see by the graph below that I just copied there have been dozens of additional earthquakes. I included a graph of continental U.S. for comparison.