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.