UPDATE 1-17-2018: the Epicentral app is no longer available, but an even better one is. Check out QuakeFeed Earthquakes. Includes customizable alerts. It’s the one I use now. Free, with in-app purchases.
(the following is provided for historical reference)
Here’s a handy iPhone app, especially if you were in Southern California at 4:53 pm today. It’s called Epicentral and it tells you where and when and how big the earthquake was.
Here’s the link.
In case you wondered: Anza Borrego Desert State Park, magnitude 5.7.