People who witnessed 4.7 earthquake said it sounded like "Bang Bang Bang!"

Which would be an indication of the earth sort of turning into an ocean wave and hitting buildings. I have seen this sort of effect in Malibu Canyon heading towards a church in I believe 1979 or around then.It makes the earth look like an ocean wave as it comes towards you and then when it hits a building it makes a sound like "Bang!" one or more times as it hits buildings.

However, usually in California at least you  don't start worrying about earthquakes until you get over a 5.0 or so because people generally don't die until the quake gets bigger than a 5.0 earthquake. However, there are always exceptions to every rule.