Earthquakes Shake the East Bay

Experts say the location of twin earthquakes has been active for the past 40 years.

By RJ Middleton
|  Friday, Oct 21, 2011  |  Updated 10:49 AM PDT
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The East Bay was jolted by a significant aftershock tonight after a 4.0 magnitude earthquake earlier today.

The East Bay was jolted by a significant aftershock tonight after a 4.0 magnitude earthquake earlier today.

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The Great California ShakeOut

Nearly 9 million people participated in the state's biggest earthquake preparedness drill ever. Students and office workers attempted to "drop, cover and hold on" when The Great California Shakeout began at 10:20 a.m.
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At 8:16 p.m. another earthquake hit the East Bay near Berkeley. This one was 5.1 miles deep, and while initially listed as a 3.9 magnitude, later changed to a 3.8 magnituede.

The second shaker was a little deeper than one that hit at 2:41 p.m., but in the same general area.

The previous one was first listed as a 4.2 magnitude, then reclassified as 4.0.

There was no damage reports from either earthquake.

[Here's the United States Geological Survey's shaker map for the 8:16 p.m. earthquake.]

The evening temblor created a large jolt in San Francisco's Civic Center area and was felt ina larger region of the Bay Area. People as far away as Morgan Hill said they felt the evening quake.

One person in the East Bay Tweeted that the evening quake felt more like a rolling motion, where the earlier one was more of a jolt.

Both quakes hit on the Hayward fault.

A scientist at USGS told NBC Bay Area that he was not surprised that there were two shakers in the same areat. He said the area just south of the Cal campus has been a known hot spot for the past 40 years. He said there is no cause for alarm that the movement could be a foreshadowing of a bigger earthquake. He said the area is "acting like it always has."

Special Section: Earthquake Info, Maps, Resources

The real earthquakes hit on the same day as California's Great ShakeOut earthquake drill.

Millions of people participated in the 10:20 a.m. duck, cover and hold on event.

While many participated in pre-arranged programs at school and work, families and individuals also took part at home.

Emergency officials said families should talk about what might happen if an earthquake shakes the area where they live. Then use this link to play audio of the earthquake drill and instructions that others will be hearing as they take part in the drill by:

  • Drop, Cover, and Hold On: Drop to the ground, take cover under a table or desk, and hold on to it as if a major earthquake were happening. Stay down for at least 60 seconds.
  • While still under the table, or wherever you are, look around and imagine what would happen in a major earthquake. What would fall on you or others? What would be damaged? What would life be like after? What will you do before the actual earthquake happens to reduce losses and quickly recover?
  • Optional) Practice what you will do after the shaking stops.
  • After your drill is complete, have discussions about what was learned and incorporate these lessons into your disaster plan.

San Francisco Mayor Ed Lee was one of the people who participated in the drill. He ducked and held with a group of school children in the City.

“The question is when, not if, there will be a major earthquake in the San Francisco Bay Area.  Emergency preparedness drills like the Great California ShakeOut will help save lives in the next disaster. The safest thing to do during an earthquake is to drop, cover and hold on," Lee said.

Lee said today’s 4.0 earthquake centered near Berkeley on the Hayward Fault is another reminder that we have to be prepared.

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