Extraordinary Number of US Quakes – Still Climbing

April 11, 2010
Holly Deyo

The shaking hasn't stopped after a 7.2 earthquake rattled the U.S. and Mexico Easter Sunday. Yesterday around 2 a.m. local time, a respectable 4.5 quake rattled San Diego, which was followed by more than a dozen Richter 3's in the same area.

The most events I can ever recall for the U.S. was 1,482 on May 3, 2008. Normally the USGS registers around 700-800 events in America that show on the US maps. This includes all quakes occurring in Hawaii, Alaska and Puerto Rico. There's a lot of real estate where quakes can shake.

Maps start to look interesting when they hit 1,100 shakes. Aftershocks from the Easter quake have rocketed this tally way beyond anything we've experienced in recent years. U.S. quakes are approaching the 4,000 ground breaking benchmark.

When you click the map on the right, you can read the number of quake events both for the Cal-Nevada area as well as the U.S. total. Over 3,700 quakes have hit the U.S in the last week. Of those, these areas account for 161 shakes: Puerto Rico – 37, Hawaii – 7, and Alaska – 117. Another 285 are scattered throughout Washington, Yellowstone/Montana, Utah and in a "smiley face" across New Mexico, Oklahoma, Arkansas and Missouri. That leaves the vast majority – over 3,270 – pummeling California. That is mighty!

Because so many earthquakes have occurred atop each other, it's hard to get a good grasp of just how many have struck since the jaw-rattling 7.2. Clicking the top map brings up a much larger version showing Mexico and southern California.

Quakes are concentrated right on the border and extend southeast to the Baja Peninsula and north to the Salton Sea. The whole area is positively inflamed with quake activity.

The small inset maps only tracks Mag. 1+ quakes for a week before they fall off. It's unfortunate that the larger "green" map plots events in gray since they're harder to see. However, the more you study the map, you'll be surprised how many "stars" your eyes pick up.

The May 4th major event is designated in red and looks like it happened after the rest. This quake had to be marked in again since it was buried in aftershocks and impossible to see locate.

Below, a Google Earth map has been included, which ties into the USGS database. Even looking at this map, it's impossible for the eye to distinguish over 3,500 individual quakes. This further reinforces that certain areas are getting hammered as quake after quake hits the same spots. Looking at the Earthquake List for Map California Nevada, you can see various locations popping up time and again.

One other thing to consider when looking at the Google map is the line in red. This marks a plate boundary which are always busy with quake activity. The North American Plate boundary ties into the San Andreas Fault starting just off-shore of northern California by Point Arena and snakes south before running its course on the east side of the Salton Sea just above Mexico. Both of these factors – a major fault and a tectonic plate boundary – place massive stress on western California.

The interesting thing to note on this map is the distinct march of quakes northward from the main shake. The greatest number of temblors isn't concentrated right at the heart of the 7.2 quake, but clustered on the border extending into both countries. Hopefully this is as far as they travel and leave San Diego and Los Angeles alone.