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 other governmental and nongovernmental organizations to bring earthquake early warning to California. Major milestones in these efforts were 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). These efforts were funded by $10 million dollars allocated in the 2016-17 budget. This funding is being used to install or upgrade over 180 seismic sensors, which will allow them to transmit real-time data. Funding is also going to the research and development of new technologies to receive warnings and provide auditory or automated actions and provide communication, education, training and outreach.

Cal OES recieved $15.75 million dollars in the 2018-19 budget to complete sensor installation or upgrade the 283 remaining sensors and support the Earthquake Early Warning Advisory Board.

Cal OES is working diligently with public, private and non-profit partners to develop new pathways to get alerts 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 in the first part of 2018. Earthquake early warning will be moving from the lab and test cases to ones that can be seen and protect larger groups of people.

Cal OES is surveying the marketplace for government agencies, universities, or other organizations to provide recomendations on how to best complete the build-out of the California Earthquake Early Warning System. It can be viewed 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 and devices before the anticipated strongest shaking arrives in affected regions. Seconds to minutes of advance warning can provide opportunity to take life-saving actions like Drop, Cover, and Hold On.

When an earthquake occurs, two main forms of seismic waves are produced. The strongest shaking resulting from the S-wave, that moves more slowly, is preceded by the weaker, less damaging P-wave. Technology now exists that can detect the energy from P-waves 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 warning to projected areas of impact before the strong shaking that radiates from the epicenter, or earthquake source.


Earthquake Early Warning Basics


Potential Benefits:

  • Pubic Warning – Alert individuals to Drop, Cover, and Hold On or safely stop vehicles.
  • First Responder Mobilization – Open fire station doors for rapid deployment of emergency response equipment and personnel.
  • Medical Services – Notify surgeons and dentists to 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 by automatically slowing and stopping trains, clearing bridges, and diverting inbound airport traffic.
  • Workplace Safety – Evacuate employees to safe locations, initiate elevator recall procedures to ground floor, place sensitive equipment in safe mode, secure chemicals and hazardous materials, and halt production lines to reduce damage.



  • The earthquake early warning system in California will be able to provide up to 90 seconds of warning prior to strong shaking. 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 station. 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 1-3 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 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.



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