A few weeks after a magnitude-7.1 earthquake struck central Mexico on Sept. 19, 2017 — leaving hundreds dead and dozens of buildings destroyed — USGS seismologist Elizabeth Cochran and a team of experts mobilized to Mexico City to assess the performance of the Mexico Seismic Warning System (Sistema de Alerta Sísmica Mexicano or SASMEX)  and the public’s perception of the alerts.

In the company of only Japan and Taiwan, Mexico is one of few countries equipped with a seismic warning system that currently broadcasts publicly. Mexico has been broadcasting in a public regional capacity since 1993 via the Mexico Seismic Warning System, which currently has more than 90 sensors in central and southern Mexico.

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Although no one can reliably predict earthquakes, today’s technology is now advanced enough to rapidly detect seismic waves as an earthquake begins and send alerts to surrounding areas before damaging shaking arrives.

“Mexico is one of just a few number of  places around the world that has a warning system and this was also one of the rare times  an early warning system had been activated for a significant earthquake,” said Cochran. “We were interested in how people reacted to the alerts and their overall perceptions of the system in the immediate aftermath of this destructive earthquake.”

Discussions the team had included the technical development of the system, and challenges to ensure the alerts have the maximum benefit to the population of Mexico.

 “We wanted to learn from the experiences of SASMEX in order to apply some of those lessons to the earthquake early warning system we are developing here in the U.S.,” Cochran said.

The Earthquake Engineering Research Institute selected Cochran to join their reconnaissance team of  recognized expert scientists to assess the warning system’s performance.  The team also included Dr. Richard Allen (University of California, Berkeley),  Dr. Scott Miles (University of Washington), and Diego Otegui (University of Delaware).

Earthquake Aftermath: Recon Team Studies System Performance

Upon arrival to Mexico City, the  EERI team visited the Centro de Instrumentación y Registro Sísmico (CIRES) that operates SASMEX. There, they learned details about how the system performed, including when alerts were issued to Mexico City during the magnitude 7.1 quake. The system issued an alert 3-5 seconds after the initial seismic wave arrivals, which were strongly felt throughout the system.   

The team spent several days visiting a series of locations, including a private school equipped with a dedicated siren system since 1993. The school experienced significant damage to two buildings on their campus, which were the administrative and preschool structures. During the earthquake, the teachers and students began evacuation as soon as shaking began but were unable to complete evacuations due to the strength of shaking. They chose to shelter in place and no injuries occurred at the school. 

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The recon team also interviewed dozens of locals -- from Uber drivers to business owners --to understand what they expected from the system, in addition to how they responded to the alert. The warning came only after earthquake shaking began because the epicenter was so close to the city.

“Despite the late warning in Mexico City for the nearby M7.1 earthquake, people view the early warning system as necessary and valuable. They feel that since the technical capability exists to issue warnings, it should be used.  It doesn’t prevent all damage or losses from earthquakes, and we knew that, but it does provide information to people,” Cochran said.  “And, it turns out to also be a useful tool for strengthening their earthquake awareness and response to earthquakes.”

Coincidentally, the  Sept. 19, 2017,  7.1-magnitude Mexico earthquake occurred  two hours after a national earthquake drill to commemorate the 32^nd anniversary of the 1985 Mexico City earthquake. That devastating 1985 quake was what prompted the implementation of SASMEX.

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The earthquake occurred only a short time after the sirens were sounded for the national exercise, but since shaking started prior to the alert sounding there was no confusion that this alert was an extension of the drill. People noted that they reacted more quickly when shaking started because the recent drill reminded them how to respond during shaking or when the siren sounds.

U.S. Earthquake Early Warning: ShakeAlert

Nearly 50 million Americans are at risk due to earthquakes on the West Coast of the United States.  Massive earthquakes on the Cascadia Subduction Zone or the San Andreas Fault system could cause billions of dollars in damage and cost thousands of lives.

“When fully operational, the ShakeAlert earthquake early warning system will save lives and reduce injuries and property damage,” said Robert  de Groot, Coordinator for Communication, Education, and Outreach for the USGS ShakeAlert Earthquake Early Warning Project.

The USGS ShakeAlert system does not yet support public warnings, but in the near  future a limited rollout will enable selected early adopters to develop pilot implementations that take automatic protective actions or notify trained personnel. The goal is to demonstrate the system’s utility and develop technologies that pave the way for broader use.

Learn More

Published report from reconnaissance team: http://science.sciencemag.org/content/358/6367/1111

Other resources:

https://earthquake.usgs.gov/earthquakes/eventpage/us2000ar20#executive

https://earthquake.usgs.gov/archive/product/poster/20170919/us/1506025242898/poster.pdf