Overview

A user of ShakeAlert™ receives a message like this on the screen of his computer. The message alerts the user to how many seconds before the shaking waves arrive at their location and the expected intensity of shaking at that site. The shaking intensity follows the Modified Mercalli scale; an intensity of VI, as shown here, would mean the shaking is felt by everyone, people find it difficult to stand, and structures may suffer some damage. The warning message also displays a map with the location of the epicenter, the magnitude of the quake, and the current position of the P and S waves. In this example, the alert is for the ShakeOut scenario earthquake. (Public domain.)

Earthquake early warning systems use earthquake science and the technology of monitoring systems to alert devices and people when shaking waves generated by an earthquake are expected to arrive at their location. The seconds to tens of seconds of advance warning can allow people and systems to take actions to protect life and property from destructive shaking.

Even a few seconds of warning can enable protective actions such as:

• Public: Citizens, including schoolchildren, drop, cover, and hold on; turn off stoves, safely stop vehicles.
• Businesses: Personnel move to safe locations, automated systems ensure elevators doors open, production lines are shut down, sensitive equipment is placed in a safe mode.
• Medical services: Surgeons, dentists, and others stop delicate procedures.
• Emergency responders: Open firehouse doors, personnel prepare and prioritize response decisions.
• Power infrastructure: Protect power stations and grid facilities from strong shaking.

EEW systems are currently operating in several countries, and others are building them. Since 2006 the USGS has been working to develop EEW for the United States, with the help of several cooperating organizations including the California Geological Survey (CGS), the California Institute of Technology (Caltech), the California Office of Emergency Services (CalOES), the Moore Foundation, the University of California, Berkeley, the University of Washington, and the University of Oregon. The goal is to create and operate an EEW system for the highest risk areas of the United States beginning with the West Coast states: California, Washington, and Oregon.

A demonstration EEW system called ShakeAlert™ began sending test notifications to selected users in California in January 2012. The system detects earthquakes using the California Integrated Seismic Network (CISN),an existing network of about 400 high-quality ground motion sensors. CISN is a partnership between the USGS, State of California, Caltech, and University of California, Berkeley, and is one of seven regional networks that make up the Advanced National Seismic System (ANSS).

In February of 2016 the USGS, along with its partners, rolled-out the next-generation ShakeAlert™ early warning test system in California. This “production prototype” has been designed for redundant, reliable operations. The system includes geographically distributed servers, and allows for automatic fail-over if connection is lost. This next-generation system will not yet support public warnings but will allow selected early adopters to develop and deploy pilot implementations that take protective actions triggered by the ShakeAlert™ warnings in areas with sufficient coverage. The USGS has published an Implementation Plan with the steps needed to complete the system and begin issuing public alerts.

Next Steps

Earthquake sensor density: California versus Japan. New sensors need to be added in California to shorten the CISN sensors spacing to approximately 12 miles to facilitate timely EEW. The shorter the station spacing, the smaller the blind zone will be because warnings can be issued faster. (Public domain.)

Improving the sensor network

The most important component of an earthquake early warning system is a dense network of seismic and geodetic stations with robust communications. Future development of the warning system will include the installation of larger numbers of seismic stations and upgrading station telecommunications. The current seismic station densities in California are currently much lower than the Japanese public alert system. New sensors are needed in California to reduce earthquake detection times allowing warnings to be issued faster.

Additional Sources of Ground Motion Measurements

In the future, additional sources of ground motion observations can be integrated in the EEW algorithms. Additional data may be able to help reduce the time to detection and improve early estimates of earthquake magnitude and location.

Some examples include:

1. Real-time GPS displacements. Throughout California there are over a hundred high sample rate Global Positioning System (GPS) sensors that provide very accurate measurements of ground displacement. Data is collected from several regional GPS network including from the Southern California Integrated GPS Network and Bay Area Regional Deformation Network. Measurements of ground displacement can be very useful for identifying large earthquakes that can have centimeters to meters of ground displacement. It can be challenging to recover displacements in real time because very accurate information is needed on the orbits of the GPS satellites. Several research groups within the USGS and at collaborating universities are currently developing algorithms to estimate GPS positions accurately in real-time and methods to integrate the information into existing EEW algorithms.
2. Low-cost sensors hosted in homes, businesses, and schools. New sensor technologies have greatly reduced the cost of lower-resolution strong motion seismometers. These sensors use micro-electro-mechanical systems (MEMS) accelerometers that are contained on a single computer chip. Scientists have been exploring ways to utilize theses sensors to increase the number of strong motion sensors in urban areas. Two examples include the Quake-Catcher Network and the Community Seismic Network that install low-cost sensors in homes, businesses, and schools.

A GPS antenna in southern California. Many of the GPS stations in California are currently being converted to send data in real time back to the networks. And, algorithms are being developed to process and use these data in the earthquake early warning alerts. (Public domain.)

MEMS accelerometer being tested for earthquake detection. These lower cost sensors may be used in urban areas to better map variation in shaking amplitudes across a region. In addition, the data may be useful for reducing the time needed to detect an earthquake. (Public domain.)

Issuing Warnings

Every available technology will be used to ensure that EEW messages reach as many people and as quickly as possible. Most currently available mass messaging technologies are too slow for EEW. Unlike the Japanese system, here in the US we are unable to send messages to large numbers of cell phones without delays. However, many promising technologies are on the horizon like broadcast text messaging, smartphone apps and recent upgrades to the national Integrated Public Alert and Warning System (IPAWS). EEW may also open the door to many public/private partnerships.

Information on the ShakeAlert Product

Public Outreach

The EEW system must be connected with users of the warning ahead of time, and therefore requires a public outreach effort upon implementation to make people aware of the system and how to respond to it. Responses are most effective when automated and pre-established so the recipients know what action to take when they get a warning.