An earthquake is when the ground shakes because of movement under the earth's surface.
California is a place where earthquakes happen pretty often because it's on a big crack in the earth called the San Andreas fault.
Scientists who study earthquakes and try to predict when they might happen have something called a forecast. It's like when your mom or dad tells you it's going to rain tomorrow, they are predicting the weather.
The California earthquake forecast is when these scientists use all kinds of special tools and information to try and guess when an earthquake might happen next and how strong it might be. They study the way the land has moved in the past and look for signs that it might be about to move again.
It's important for people who live in California to know about these forecasts so they can be prepared. They might need to make an emergency kit with things like water, food, and flashlights in case the earthquake happens and they can't leave their house for a while.
So in summary, the California earthquake forecast is when scientists use special tools to guess when an earthquake might happen next, and it helps people who live there be prepared.