Earthquake early warning challenges

Written by: Miguel Nevis, Ph.D. Candidate, Georgia Institute of Technology (@ Waves2Miguel)

A new study examines the challenges of earthquake early warning systems, such as latency, and how to improve systems.

Citation: Nevis, M. , 2020, Earthquake Early Warning Challenges, Templore, http://doi.org/10.32858/temblor.093.

ShakeAlert, an earthquake early warning system (EEW), began sending alerts for an upcoming earthquake to the California state public in late 2019. The warning system is similar to thunderstorm mechanics, says Robert Michael de Groot, ShakeAlert’s national coordinator for communications, education, and USGS (USGS). Just as lightning precedes thunder, so faster seismic waves (P waves) earthquakes precede larger and more harmful waves (S waves). EEW systems attempt to detect large earthquakes and provide a warning before harmful vibrations arrive.

Seismic early warning systems typically use seismometers to detect incoming P-wave. When the vibration is felt, a signal is sent to the local seismic authority, which quickly sends an alert to those in the area who are most likely to feel the vibration, hopefully before the most damaging S waves arrive. Credit: NoPineapplesOnPizza (CC BY-SA 4.0)

However, people are divided over how useful EEW systems are. Now, a recent Earthquake Spectra paper by David Wald, also a seismologist at USGS and a member of EEW’s external working group, analyzes the limitations of early warning systems and discusses how recognition of these limitations can make ShakeAlert more successful.

Thirty years of EEW

EEW systems are not a new concept. Mexico City has had a public warning system since 1993 and the Japan Meteorological Agency began issuing alerts to the public in 2007. In 2012, USGS began developing ShakeAlert, an EEW system for California, Oregon, and Washington. ShakeAlert developers have partnered with about 60 organizations in all three states, such as universities or transit authorities, working to develop warning applications or automatic actions (such as automatically slowing trains when an earthquake begins to vibrate). ShakeAlert Pilot Project has been sending alerts to partner organizations since late 2018.

An example of a warning issued by ShakeAlert. Credit: Erin R. Burkett, Douglas D. Given and Lucile M. Jones; Public domain

The public got its first experience with the system in California last October. If the ShakeAlert system detects an earthquake of 4.5 or higher, mobile phones in areas that are shaken by light or higher (IV intensity or higher on the modified Mercalli scale) will receive an FEMA alert via wireless emergency alerts (WEA), similar to warnings issued in extreme weather or children kidnapping. Warnings can also reach audiences with mobile apps like MyShake or ShakeAlertLA. The spread of public warning plans in Washington and Oregon has been affected by the current epidemic, but experts expect it to first appear next year.

Challenge: warning times

One of the biggest challenges EEW faces are warning times. The warning time corresponds to the time between the users receiving an alert and the time the vibration reached their site. Many media reports and EEW posts indicate that warning times can range from seconds to minutes. However, father notes, using estimates from idealized models, providing people in areas with strong vibration just a few seconds of warning or even late warnings that arrive after harmful waves.

The earthquake site is the most important factor contributing to warning time issues. If an earthquake strikes away from population centers, such as in cases of marine earthquakes along the coasts of Oregon, Washington, or Japan, warning times will be longer due to greater distances. But in places like California, where most earthquakes have internal origins, many people will feel shaken before receiving an alert. There is not much that can be done to improve warning times when shaking occurs directly under the person.

The San Francisco Peninsula is home to the San Andreas error – which appears here as it runs beneath the reservoirs on the left side of this northern view – alongside more than 1.6 million people. Credit: Doc Searles (CC BY-SA 2.0)

A father indicated that the devices also have a major impact on whether an alert arrives before a major event. In one test conducted in Auckland, WEA Alerts showed that 85 percent of phones receive alerts until 5 seconds or more after the alerts are issued – which in many cases will be too late to provide a warning before the vibration begins. But most mass messaging systems aren’t built to ShakeAlert speeds, as de Groot explains. USGS works with FEMA, FCC, and mobile operators to improve WEA capabilities and bring them more in line with ShakeAlert speeds. Other options for sending alerts include mobile apps like MyShake, but a parent raises concerns that they haven’t been tested with a large number of users receiving an alert.

Another important component of EEW systems are algorithms that estimate Earth’s vibration levels. Much research has been devoted to this aspect of EEW, as these algorithms affect warning times as well as the number of valid (and incorrect) alerts issued. ShakeAlert uses a set of algorithms that detect and characterize the earthquake (location and force) and that predict ground shake levels in different regions. Estimates are initially calculated in the first few seconds after the P wave arrives, but are updated as more seismic data becomes available. Many seismologists initially thought that the first few seconds (about 3 seconds) would be sufficient to correctly assess the magnitude of a large earthquake. However, as his father notes in his study, recent observations of the earthquake attacks indicate that extra time is necessary.

However, even with the extra time, the system “is still able to provide warnings at the right time,” says Men-Andrin Meier, a seismologist at Caltech who has studied both ShakeAlert and Japanese system algorithms. Recent results also indicate that improved warning times and reliability can be achieved.

Challenge: action

What happens once you receive a warning also affects the effectiveness of EEW systems. Father reported that she conducted limited studies on the subject. The U.S. Geological Survey is currently collaborating with many partners who are testing their ideas for automatic measures, such as slowing trains, closing water valves and opening emergency doors, which may inspire the new EEW industry, says de Groot. Social studies are also being conducted to understand the impact of receiving earthquake warning on the general public and to understand how to communicate effectively about how citizens respond to this. But slowing trains or covering up under your desk also takes some time, and as a parent notes, this time isn’t usually included in EEW connections.

In the earthquake, descend to the ground, cover your head and body and wait. Credit: Earthquake Country Alliance

Public and media interest in ShakeAlert has created a major opportunity to educate the public about risk mitigation, risk preparation strategies and the dissemination of scientific information. A parent says EEW should be strengthened in a larger framework for other seismic information products. For example, he says, some entities will be better served with more accurate information products after the earthquake that determine the intensity of vibration or that estimate deaths and economic losses to help them prioritize disaster response. A parent says EEW is “not a panacea” and will not eliminate all catastrophic consequences.

Overall, Wald says, though, EEW would be beneficial for mitigation efforts and there is potential for improving warning times. The interest gathered around systems like ShakeAlert also provides an opportunity to better communicate with what the public can expect from the system, but also to discuss the earthquake’s ability to withstand a greater framework of actions that individuals and society can take to improve preparedness.

In-depth reading

Father, DJ (2020). Practical limitations for earthquake early warning. Earthquake spectra. https://doi.org/10.1177/8755293020911388

Minson, SE, Meier, MA, Baltay, A.S., Hanks, T.C., Cochran, E.S. (2018). Earthquake Early Warning Limits: Timing of Ground Traffic Estimates. Science Advances, 4 (3), eaaq0504. https://doi.org/10.1126/sciadv.aaq0504

Melgar, D., & Hayes, GP (2019). Description of large earthquakes before rupture is completed. Science Advances, 5 (5), eaav2032. https://doi.org/10.1126/sciadv.aav2032

Li, Z., Meier, MA, Hauksson, E., Zhan, Z., and Andrews, J. (2018). Machine learning of seismic wave recognition: application to earthquake early warning. Geophysical Research Letters, 45 (10), 4773-4779. https://doi.org/10.1029/2018GL077870

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