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Research Geophysicist with the United States Geological Survey (USGS), Brad Aagaard, shows members of the media a series of images that illustrate how shock waves from an expected catastrophic 7.8 magnitude earthquake on the San Andreas Fault would likely fan out across southern California.
For a long time geologists believed it was unlikely that a massive quake in say, San Diego could reach all the way to San Francisco.
But a new study published by the journal Nature says that kind of mega-quake isn't out of the question.
Here to explain is Kate Hutton, a seismologist with the California Institute of Technology.