For Android users:
MyShake is a new smartphone-based seismic network developed by UC Berkeley Seismological Laboratory and the Deutsche Telekom Silicon Valley Innovation Center.
MyShake is a free app for Android phones that has the ability to recognize earthquake shaking using the sensors in every smartphone. The app runs "silently" in the background on your phone. Our goal is to build a worldwide seismic network and use the data to reduce the effects of earthquakes. MyShake also provides users with information about recent earthquakes and significant historical earthquakes.
More about the MyShake project
For iOS users:
MyQuake maps earthquakes that are occurring near you and across the globe. MyQuake also shows large damaging historic earthquakes in California, and calculates the shaking intensity at your locations for these past and present earthquakes. MyQuake is completely ad-free and gives you a smooth, intuitive user interface for you to learn everything about earthquakes, keeping you informed and preparing you for the next big earthquake.