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October 7, 2019

Next week, USGS and the nation commemorate the 30th anniversary of one of the most destructive earthquake disasters in U.S. history – the 1989 Loma Prieta earthquake in northern California. The magnitude 6.9 quake struck on October 17 in the southern portion of the San Francisco Bay Area near Santa Cruz and was responsible for the deaths of 63 people and more than 3,500 injuries.

There is something else to remember on this anniversary – the development and testing of a forerunner of the USGS ShakeAlert® Earthquake Early Warning System.

Looking down on collapsed, severely damaged viaduct section of highway.
Aerial view of collapsed sections of the Cypress Street viaduct of Interstate Highway 880 in Oakland, California, damaged as a result of the magnitude 6.9 Loma Prieta earthquake on October 17, 1989. The epicenter was located near Loma Prieta peak in the Santa Cruz Mountains, approximately 14 km (9 mi) northeast of Santa Cruz and 96 km (60 mi) south-southeast of San Francisco and Oakland (Credit: H.G. Wilshire, USGS).

Origins of Earthquake Early Warning

Wherever people live with earthquakes, there is a desire for an early warning that shaking is imminent. Even as far back as 1868, following a magnitude 6.8 earthquake on the Hayward fault, the San Francisco Daily Evening Bulletin published an editorial proposing an early warning system. Calls echoing that desire continued throughout the 20th century in countries as far off as Iran, Italy, Japan, and Mexico.

In the United States, the first serious proposal for such a system came from USGS geophysicist Tom Heaton in 1985. Dr. Heaton’s pioneering insight was ahead of its time, but the technology available in 1985 was not adequate for the system he proposed.

However, a few years later, other USGS scientists would temporarily use some of Heaton’s innovative ideas after the Loma Prieta earthquake to try to safeguard the lives of rescue workers in the Bay Area. The intense shaking from the mainshock of Loma Prieta collapsed a 1.6-mile (2.5-kilometer) section of the Nimitz Freeway (referred to as the “Cypress Structure”) along I-880 through Oakland. As rescuers worked to free people trapped in the rubble, the risk of aftershocks damaging the freeway further and injuring the workers became apparent. So USGS scientists set up a temporary system that radioed alerts to the workers whenever there was a significant aftershock that might shake the Nimitz. During its six months of operation, the system sent warnings for 12 earthquakes greater than magnitude 3.7.

Video Transcript
Retired seismologist David Oppenheimer reflects on the first prototype earthquake early warning system used during the 1989 Loma Prieta earthquake. Scientists deployed an analog system to notify first responders of impending earthquake activity as they worked on rescue efforts at the Cypress Viaduct collapse in Oakland, CA.

Seeds of ShakeAlert

The backbone of an earthquake early warning system is a widespread and robust network of seismometers. In the United States, the first regional seismic networks were begun by research institutions and universities like Caltech; University of California, Berkeley; and the University of Washington. These regional networks and others were later brought together and coordinated by the Advanced National Seismic System (ANSS) in 2000.

Around the same time that ANSS formed, seismometers were advancing from analog to digital recordings, which allowed them to log data much more quickly and accurately. Additionally, high-bandwidth data communications were becoming more common, allowing seismic stations to quickly transmit their data across greater distances.

Meanwhile, other countries had set up or begun exploring earthquake early warning systems of their own, often following tragic earthquake disasters. Mexico, for example, began its public earthquake early warning system in 1991 after the deadly 1985 magnitude 8.0 Guerrero earthquake, while Japan began theirs in 2007, spurred on by the lethal 1995 magnitude 6.9 Kobe earthquake.

Scientists and planners in the United States hoped to be able to put those hard-learned lessons in effect here before a deadly earthquake struck within our borders. The stage was now set for the United States’ own earthquake early warning system, which would come to be known as “ShakeAlert.”


A USGS technician services a ShakeAlert sensor station in the San Francisco Bay area
An electronics technician performs maintenance on a ShakeAlert seismic sensor station located in the San Francisco Bay Area. These stations include strong-motion accelerometers, solar panel and battery power systems, and communications and telemetry equipment for communication with the wider ShakeAlert network (Credit: Paul Laustsen, USGS).

Building a Strong Foundation

In 2006, USGS; Caltech; University of California, Berkeley; the Southern California Earthquake Center; and the Swiss Federal Institute of Technology in Zurich formed a partnership to set the standards for what would constitute ShakeAlert. These standards included specifications for seismic network equipment, what kinds of data analysis would be needed to recognize that an alert was required, and how best to distribute alerts to users quickly so they could take protective actions such as those described in the “Drop, Cover, and Hold On” campaign.

After all, earthquake early warning is not simply a matter of notifying people whenever there is an earthquake. It is also about making sure that the information they get about the shaking is timely and meaningful for the hazard they may face, and that they know what protective actions to take, if needed.

The key for these organizations, then, was to develop computerized techniques to characterize potentially damaging earthquakes fast enough to notify people in harm’s way before shaking from a quake reached them. That capability also required upgrading and increasing the density of equipment in existing seismic sensor networks, as well as improving the information technology infrastructure and scientific understanding to more accurately estimate ground shaking intensity at the user’s location.

Speed is of the essence for people to get alerts before shaking arrives at their location. Development and testing of earthquake early warning have shown that the amount of warning time is dependent on the proximity of seismic stations to the earthquake, the distance of a user from the epicenter, and how one receives the alert. Thus, the public and other end users may receive an alert before, during, or after shaking arrives at their location.


ShakeAlert Logo
ShakeAlert® is an earthquake early warning system that detects significant earthquakes so quickly that alerts can reach many people before shaking arrives. ShakeAlert is not earthquake prediction, rather a tool that indicates an earthquake has begun and shaking is imminent.

USGS ShakeAlert Earthquake Early Warning System is Born

USGS and other scientists and planners are not only concerned about earthquakes in California but also are looking into earthquake early warning for the Pacific Northwest. Just off the coast of Washington, Oregon, and northernmost California, great megathrust earthquakes on the Cascadia subduction zone not only have the potential to cause damage via shaking, but they can also generate tsunamis. To top it off, because much of the Cascadia subduction zone lies offshore, getting seismometers close to the faults is difficult, making earthquake early warning more challenging.

In 2012, the Pacific Northwest Seismic Network, which is an ANSS regional network operated by the USGS, the University of Washington, and the University of Oregon, joined the earthquake early warning efforts that began in California. Their goal was to extend the USGS ShakeAlert Earthquake Early Warning System across the entire U.S. mainland Pacific Coast. In fact, the partnership grew to include support from the Gordon and Betty Moore Foundation, the City of Los Angeles, and the state governments of California, Oregon, and Washington.

Scientists, engineers, and emergency managers with these organizations are now focusing on making the best use of early warning for the different types of earthquake hazards faced across the three states.


animation showing earthquake shaking moving south toward San Francisco on the San Andreas Fault
The choice when issuing earthquake warnings is to: 1) issue alerts for weak shaking and potentially provide long warning times, but risk sending alerts for the many events that do not go on to produce damaging ground shaking, or 2) issue alerts only when ground shaking is expected to be damaging, with the tradeoff that the alert will be sent much later, reducing the amount of time available to take action.

Testing and Refining the Alerts

The next step for successful implementation of an earthquake early warning system was to do pilot testing of the alerts. ShakeAlerts from the USGS ShakeAlert Earthquake Early Warning System were issued to those people and institutions that would need them the most, such as hospitals, schools, public transportation operators, and emergency responders. From 2012 to 2016, the ShakeAlert system was updated and refined using the feedback of early adopters like the Bay Area Rapid Transit system.

[Read more about ShakeAlerts and BART]

In 2014, Congress began providing appropriated funding to the USGS that was designated specifically for ShakeAlert, allowing the USGS and partners to build out the system and continue research on earthquake early warning.

After incorporating feedback from early adopters into the USGS ShakeAlert Earthquake Early Warning System, the USGS made ShakeAlerts available to select technical users throughout the West Coast in 2017. These select users included transportation system operators and municipal water managers who developed ways to use ShakeAlerts to promote public safety and resilience. The pilot stage also allowed USGS and its partners to make improvements to ensure that the ShakeAlert system functioned well across all three states. Meanwhile, USGS and its partners coordinated on how a public earthquake early warning system would function, including appropriate education and training for those using ShakeAlerts.

Decades of work and close collaborations and partnerships led to a series of rollout phases on the path to public alerting. In 2018, USGS declared that ShakeAlert was “ready to roll” and available to alert personnel via automated delivery to computers and applications within organizations. The next phase was to test limited public alerting in Los Angeles County using a cellphone app developed by the City of Los Angeles, which debuted in early 2019.

As the sensor network expands and the number and type of ShakeAlert users increase, more data are collected on the system’s performance and how the public responds to the alerts. The USGS ShakeAlert Earthquake Early Warning System will continue to be improved and refined to better serve the needs of its users.


Making the Message Matter

In parallel with the development of the technology to produce and deliver ShakeAlerts, USGS and its partners are also studying how users react to alerts and how to best educate the public about the ShakeAlert system’s capabilities and limitations. After all, the most technologically advanced system in the world is useless unless people know what to do in response to alerts.

As part of ensuring appropriate user responses to alerts, ShakeAlert and its partners have implemented an extensive social science research effort to develop effective messaging and other resources to optimize the system’s effectiveness. ShakeAlert community members have collaborated closely to ensure that alerts are tailored to fit their individual needs, while also meeting uniform standards for both content and appearance. Sustained public education and training are essential for the successful adoption and long-term success of the ShakeAlert system.


Start with Science

USGS, its partners, and the nation’s earthquake early warning capacity have come a long way since Loma Prieta in 1989. Dozens of organizations from the public and private sectors have partnered, hundreds of seismometers have been installed, thousands of quakes have been detected, and social science research is underway. The ShakeAlert Earthquake Early Warning System is still not fully funded or built out, but each year brings more capacity and refinement, helping to potentially save lives and property.

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