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An estimated 17 million people felt 5.1 earthquake in California

An estimated 17 million people felt Friday's magnitude 5.1 quake centered in La Habra.

U.S. Geological Survey seismologist David Wald said officials received valuable information from the 16,000 reports by individuals who used the Did You Feel It? reporting system on the agency website.

“About one in 1,000 are actually reporting... That’s a pretty good [data] sample. If you’re polling for political responses, that would be a huge sample,” said Wald, who co-created and operates the DYFI system.

PHOTOS: 5.1 quake rattles L.A., Orange County

The quake was felt over a large swath of Southern California. It caused modest damage to some homes, a rock slide in Carbon Canyon and broke some water mains. Officials have not come up with a damage total.

The 5.8 earthquake in 2011 that struck Virginia and was felt across the Eastern Seaboard was reported by 144,000 people and probably felt by about 100 million people, according to Wald.

Before DYFI was created in 1999 as part of an undergraduate project at Caltech, the USGS would send postal questionnaires to ZIP Codes in an area that experienced an earthquake. People would fill it out, and it would take months to compile the information that now can be done automatically through a computer.

Wald said that unlike the torrents of information posted on Twitter and Facebook after an earthquake, the questions people fill out for DYFI are well-tuned questions that seismologists have asked for decades — streamlining the information that comes in and giving scientists usable, sortable data that help determine valuable information such as intensity and how far the shaking traveled.

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