Earthquake Early Warning

Earthquake early warning (EEW) detects and measures earthquakes fast enough that warning can be given before the strongest shaking arrives, providing seconds to minutes to prepare.

Earthquake early warning is being implemented in many locations around the world.  The 2011 Tohuku Earthquake demonstrated some of the its advantages.  The earthquake was recognized as serious within 30 seconds of its initiation offshore.  Tokyo residents had ~30 seconds warning of approaching strong ground motion.  Cell phone alarms warned millions of people when large aftershocks were likely to soon rattle them.

On the west coast of the the US, with USGS funding, Cal Tech and UC Berkeley have developed and are testing an early prototype EEW system in California.  In November, 2012, the Moore Foundation announced awarded grants to Cal Tech, UC Berkeley, and the University of Washington to develop and begin testing this prototype system.  The USGS will help coordinate these activities. 

UW's specific research objective is to develop the capability of issuing an alert tens of seconds after the onset of a large Cascadia Subduction Zone earthquake. This alert could provide from tens of seconds to minutes of warning to Puget Sound area businesses and residents before strong shaking reaches them. The UW's Pacific Northwest Seismic Network (PNSN) organized a small stakeholders workshop in February 2013 to brief potential EEW users of progress in the systems development. The meetings notes from this innitial meeting were released in March 2013. Participants have begun conversations on how EEW system alerts might be integrated into operations and communications systems to reduce losses.

A workshop has been held at the UW on Feb. 17, 2015 for announcing the release of a prototype EEW system based on that running in California for the past couple of years.

How does EEW work? (See also USGS Fact Sheet 2014-3083)
EEW is made possible by three main contributing factors:
1) Less destructive P waves travel faster than the more destructive S waves, and so will arrive first at any given location.
2) A dense seismic station network near the earthquake source can quickly detect seismic waves well before the more significant shaking will arrive at more distant population centers.
3) Data transmission to PNSN, processing at PNSN, and distribution to the end user is very fast relative to seismic travel times.
The amount of warning time increases rapidly with one's distance from the epicenter, and there will be a minimum distance from the hypocenter of the earthquake within which early warning is not possible.