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How the ShakeAlert® Earthquake Early Warning System Works
The League of Oregon Cities is partnering with ShakeAlert, the United States Earthquake Early Warning System, to inform members on earthquake risk in Oregon and what they can do to mitigate damage from earthquake shaking. Last month, we began this series talking about earthquake hazards in Oregon. Let’s continue by talking about how the ShakeAlert® System provides alerts to the public.
ShakeAlert is an early earthquake warning system that detects significant earthquakes quickly enough to alert people and automated systems seconds before shaking arrives. By providing the time until strong shaking arrives at a location, ShakeAlert can save lives and reduce injuries by giving people time to take a protective action like Drop, Cover, and Hold On, or moving away from hazardous areas.
* ShakeAlert is not earthquake prediction, rather a ShakeAlert issued by the USGS indicates that an earthquake has begun, and shaking is imminent *
Earthquakes occur when rock breaks along a fault line. This sudden release of energy creates seismic waves which travel through the Earth’s crust and make the ground shake – otherwise known as an earthquake. Earthquakes don’t occur instantaneously; instead, faults underground rupture like a zipper opening over seconds or tens of seconds.
Today, a network of seismic sensors deployed across California, Oregon, and Washington are constantly measuring ground motion. They send this ground motion data to centralized USGS processing centers. When an earthquake occurs and more and more sensors feel this ground motion, fast working algorithms at USGS data processing centers determine that an earthquake is occurring and rapidly begin to estimate the location of the rupturing fault, the magnitude - or strength- of the earthquake, and the estimated shaking intensities across the affected area. The USGS published this raw data - referred to as a ShakeAlert- to its alert server, making it available to partners to use. To activate a ShakeAlert message, at least four seismic sensors need to feel the same ground motion.
Seismic waves move fast, but not faster than the speed of sound when moving through rock (10,000 mph). Meanwhile, information recorded by seismometers is sent to processing centers at virtually the speed of light (670,616,629 mph). Algorithms take just a few seconds to calculate the intensity and area of shaking, and just a few more seconds to send out a ShakeAlert® message. So during an earthquake, many people will get an early warning about earthquake shaking prior to feeling shaking.
Approved USGS Technical Partners take the published ShakeAlert and turn it into public alerts, allowing individuals to get to a safe place before shaking starts. Examples of public alerts include a cellphone app, a federal, state, or county emergency alert push-notification on your phone, or a public address system in a building. This time can allow you to take protective action before shaking arrives at your location.
USGS-Approved Technical Partners are also working to develop more uses for ShakeAlert® messages, allowing organizations to take automated actions upon receiving an alert. In this way, you will benefit from ShakeAlert without your immediate knowledge. For example, current examples of Technical Partners using the USGS ShakeAlert data to take automatic actions include:
- slowing trains to prevent derailment
- closing bridges to prevent cars from entering vulnerable bridges and tunnels
- throttling water utility valves to prevent emptying of drinking water reservoirs
- opening firehouse doors so they are not stuck shut
- activating backup generators at hospitals to ensure continued service
Actions like these provide time to put critical infrastructure in “safe” mode so they can tolerate strong shaking and get up and running once shaking stops.
An overview of the ShakeAlert® system. Source: USGS ShakeAlert® Revised Technical Implementation Plan: https://doi.org/10.3133/ofr20181155
Last Updated 9/25/20