Earthquake Warning California is the nation’s first statewide earthquake warning system to alert people before shaking reaches them.

It uses science, state-of-the-art monitoring technology, and innovative delivery methods to alert people via mobile devices before the anticipated strongest shaking arrives in affected regions. Seconds to tens of seconds of alert can provide opportunity to take life-saving actions such as DROP, COVER, and HOLD ON.

To receive earthquake warnings, individuals and family members may download the MyShake App and ensure phone settings are adjusted to receive emergency alerts. Earthquake Warning California also offers no-cost earthquake warning resources, including:

• MyShake App: Free smartphone app that provides iPhone and Android users with audio and visual warnings [magnitude 4.5 or higher and Modified Mercalli Intensity III (weak) shaking]. Available at in the Apple App and Google Play stores;
• Android Earthquake Alerts: Android phones with updated operating systems are automatically subscribed to Android Earthquake Alerts, which uses the same technology as the MyShake App; and
• Wireless Emergency Alerts (WEAs): No-cost text messages for emergency situations [magnitude 5.0 or higher and Modified Mercalli Intensity IV (light) shaking].

Recipients of alerts will vary depending upon their distance from the epicenter of the earthquake. The closer you are to the epicenter, the less warning time there will be. If you are within 10 or 15 miles of the earthquake epicenter, you may get a MyShake notice during or after the shaking.

How is this possible?

1. In an earthquake, a rupturing fault sends out different types of waves. The fast-moving P-wave is first to arrive traveling between 3 and 5 miles per second, but the damage is caused by the slower S-waves and surface waves which travel at 1 to 3 miles per second .
2. Sensors detect the P-wave and transmit data to an earthquake alert center where the location and size of the quake are determined within seconds and updated as sensors further from the epicenter provide additional data.
3. A message from the alert center is immediately transmitted to users.

Limitations of the system

• Earthquake early warning is not earthquake prediction.
• The alert cannot come before the earthquake begins.
• The goal is for people to receive the alert before they feel shaking.
• People may receive an alert before, during, or after shaking arrives at their locations, especially if they are within 10 or 15 miles of the epicenter.
• The length of the warning depends on a number of factors. The factors include how close the seismic sensors are to each other, how quickly the data moves through the system, how significant the earthquake is, how deep it started in the earth and whether it moved through sand, solid ground or bed rock.
• Earthquake Warning System is based on innovative technology that will improve over time.
• In rare circumstances, you may receive a ShakeAlert® when there is no noticeable shaking.