California Earthquake Early Warning Program

Earthquake, Tsunami & Volcano Programs
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Status of Earthquake Early Warning in California

The California Governor’s Office of Emergency Services (Cal OES) is working diligently with the U.S.Geological Survey (USGS) and other governmental and nongovernmental organizations to bring earthquake early warning to California. Major milestones are the creation of the California Earthquake Early Warning Program (CEEWP) and the California Earthquake Early Warning Advisory Board by Senate Bill 438 (Hill and Hertzberg).

Cal OES received $10 million in General Funds from the State of California in 2016 and another $15.75 million 2018. The funding is being used to install or upgrade a total of 463 seismic sensors which complete the seismic network. The funding is also used for the research and development of new technologies; provide communication, education, training, and outreach; and support the Earthquake Early Warning Advisory Board.

Cal OES is working closely  with public, private, and non-profit partners to develop new pathways to get ShakeAlerts  to people within the next year. One method is to use datacasting, excess transmission with digital television signals to provide information to specialized receivers sparking auditory and automated actions. The distribution technology is being tested.

For more information about the current status of the multi-state USGS ShakeAlert system, click here.

What is earthquake early warning?

Earthquake Early Warning (EEW) systems use science, state-of-the-art monitoring technology, and innovative delivery methods to alert people via 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.

When an earthquake occurs, two main forms of seismic waves are produced. The faster and usually less damaging primary (P) waves precede the much slower damaging secondary (S) waves. Technology now exists that can quickly detect the energy from P-waves once they reach the surface to estimate the location and the magnitude of earthquakes and provide warning before the more destructive S-waves arrive. This makes it possible to detect a large earthquake and broadcast a ShakeAlert to projected areas of impact before the strong shaking arrives at that location.

Earthquake Early Warning Basics

1.      In an earthquake, a rupturing fault sends out three different types of waves. The fast-moving P-wave is first to arrive, but the damage is caused by the slower S-waves and surface waves.
2.      Sensors detect the P-wave and immediately transmit data to an earthquake alert center where the location and size of the quake are determined and updated as more data becomes available.
3.      A message from the alert center is immediately transmitted to users.

Earthquake Early Warning Basics


Potential Benefits:

  • Public Warning – Alert individuals to take protective actions such as Drop, Cover, and Hold On.
  • First Responder Mobilization – Open fire station doors for rapid deployment of emergency response equipment and personnel.
  • Health Care – Notify medical providers to stabilize and/or stop delicate procedures and maintain critical medical facility operations.
  • Utility Infrastructure - Safeguard energy sector grid and other utilities infrastructure for strong shaking with warning alarms and automatic controls to prevent combustions, flooding, and loss of water distribution systems.
  • Mass Transit Systems – Prevent fatal collisions or derailments by automatically slowing and/or stopping trains, clearing bridges, and diverting inbound airport traffic.
  • Workplace Safety – Employees take protective actions , initiate elevator recall procedures to ground floor, place sensitive equipment in safe mode, secure hazardous materials, and halt production lines to reduce damage.



The earthquake early warning system in California will be able to provide seconds to tens of seconds of alert prior to strong shaking.  People may receive a ShakeAlert before, during, or after shaking arrives at their locations. The length of time warning given to any location, before, or after shaking begins depends on a number of factors, including:

          • Distance between the epicenter and the closest seismic sensor stations. Generally, the first waves to arrive at a station are the less damaging P-waves that travel 2.5 - 4.5 miles per second on average. The more damaging S-waves travel at approximately 3 miles per second. The closer a station is to the source, the more rapidly the ground motion measurements from an earthquake are identified and the information about the earthquake is sent to the data processing center.
          • Data transmission speed over the sensor network from the ground motion sensors to the processing centers for dissemination to end users. Data from multiple stations must be collected and analyzed by the regional seismic networks to issue a warning. Ground motion information must be transferred from each station to the processing center. The existing network utilizes a variety of methods to send data back to the processing center to improve robustness, which includes radio links, phone lines, public/private internet, and satellite links. Delays from packaging and transmitting the data from the station to the processing center and the processing center to the recipient must be reduced to provide useful warning time.
          • Geological conditions including type of fault, depth of earthquake event, and geological features in the surrounding areas. Real-time ground motion information received from the stations is used to detect an earthquake and rapidly determine the location and magnitude of the event. Multiple algorithms (a mathematical procedure used to compute a desired result) are used to estimate the earthquake information as rapidly as possible.
          • The California Earthquake Early Warning System is based on innovative technology that will improve over time. In rare circumstances, you may receive a ShakeAlert when there was no earthquake.


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