Earthquake early warning systems: how they work, country by country

What an early warning system is

An earthquake early warning system, usually shortened to EEW, is not a prediction. It is a race. When a fault ruptures it radiates a fast P-wave that arrives first and does little damage, followed by the slower S-wave and surface waves that do the shaking people fear. Seismometers close to the epicentre record the P-wave, computers estimate the earthquake’s location and magnitude from those first seconds of data, and an alert is transmitted electronically, far faster than any seismic wave travels through rock. People far enough from the epicentre receive the alert before the strong shaking reaches them.

The physics behind that head start, including the arithmetic of how many seconds distance buys you, is explained in our companion guide on how early warning differs from a notification. This page is about the systems themselves: who runs them, where they work, how their alerts are delivered and what they can and cannot do.

How a system works, step by step

1. Detection. A dense network of seismometers, spaced tens of kilometres apart in the best systems, streams ground motion to a processing centre continuously. The first stations to record a P-wave trigger the algorithm.
2. Characterisation. Within roughly three to five seconds the system estimates the epicentre, the depth and a preliminary magnitude. Some systems, including ShakeAlert, also track the rupture as it grows, because a large earthquake keeps releasing energy for tens of seconds after it starts.
3. Ground-motion forecast. The system converts that estimate into expected shaking intensity at each location it serves. This is why alerts are gated on intensity where you are, not on magnitude: a magnitude 7 far away may deserve no alert, a magnitude 5 nearby a loud one. Our guide to magnitude versus intensity explains the distinction.
4. Decision. If expected shaking clears the threshold for an area, an alert is issued for that area. Thresholds differ by country and by delivery channel.
5. Delivery. The alert reaches people through cell broadcast to every handset in a cell, through dedicated apps, through television and radio interruptions, and through street sirens. It also reaches machines: trains brake, elevators stop at the next floor, gas valves close, surgeons pause.

Every step costs time, and the total is what creates the blind zone: the area around the epicentre where strong shaking arrives before an alert can. The USGS puts it at roughly 25 km for ShakeAlert. Offshore and deep earthquakes push the epicentre away from cities and shrink the problem; a shallow earthquake directly under a city is the case no system can help with.

United States: ShakeAlert

ShakeAlert is operated by the US Geological Survey with university and state partners. It covers California, Oregon and Washington, the three states along the Pacific plate boundary, and does not extend to Alaska, Hawaii, Nevada, Utah or the rest of the country. Public alerting began in Los Angeles County in 2019, statewide in California in October 2019, in Oregon in March 2021 and in Washington in May 2021.

ShakeAlert does not itself alert the public; it produces the detection and hands it to delivery partners. There are three routes onto a phone. Wireless Emergency Alerts reach every compatible handset in the affected area through cell broadcast, with no app and no sign-up, and are used for magnitude 5.0 and above where intensity IV or greater is expected. The Android Earthquake Alerts System receives ShakeAlert data directly and alerts Android phones at a lower threshold, from magnitude 4.5. Apps such as MyShake, run by UC Berkeley, and California’s official alert channels deliver the same detections to iPhones and Android phones that install them. Our guides explain the settings for Android and for iPhone.

What to expect: for an onshore earthquake in California, the USGS anticipates around ten seconds or more of warning in lightly shaken areas, under ten seconds where shaking is moderate, and little or none in the most heavily damaged area. A large Cascadia subduction earthquake off the Oregon and Washington coast is the scenario where the system could give coastal cities tens of seconds, because the rupture starts far offshore.

Japan: JMA Earthquake Early Warning

Japan runs the most mature nationwide system. The Japan Meteorological Agency began public earthquake early warning in October 2007, drawing on its own seismometers, the dense Hi-net network of the National Research Institute for Earth Science and Disaster Resilience, and ocean-bottom sensors off the Pacific coast. The system is woven into daily life: alerts interrupt every television and radio channel, sound on every phone through cell broadcast, stop Shinkansen trains and halt factory lines.

Japan separates two products. An EEW forecast is issued at a low threshold for institutional and automated users. An EEW warning to the general public is issued when a seismic intensity of 5-lower or higher on the Japanese shindo scale is expected somewhere, and it is delivered to the prefectures expected to feel intensity 4 or more. The distinction matters because the public alert is deliberately rare: the JMA aims for people to take it seriously when it sounds. The 2011 Tōhoku earthquake gave Tokyo about a minute of warning before strong shaking, and also exposed the system’s main weakness, an underestimate of a very large rupture in its first seconds, which has since been addressed with newer algorithms. Recent activity is on our Japan earthquakes page.

Mexico: SASMEX

Mexico’s Sistema de Alerta Sísmica Mexicano, operated by the non-profit CIRES, is the world’s oldest public early warning system. It began alerting Mexico City in 1991 and went fully public in 1993, and it is built around one geometric fact: the subduction zone that produces Mexico’s largest earthquakes lies along the Guerrero and Oaxaca coast, roughly 300 km from the capital. Sensors on the coast detect the rupture and the alert reaches Mexico City with as much as 60 seconds to spare. Coverage has since extended to Oaxaca, Acapulco, Chilpancingo, Puebla and Morelia.

Delivery is distinctive. Thousands of street loudspeakers in Mexico City sound the alert, alongside radio, television and dedicated receivers in schools and offices. Since 2025 the alert has also been delivered by cell broadcast to compatible phones nationwide, so no app is required. The system’s limits were shown on 19 September 2017, when a magnitude 7.1 earthquake in Puebla, only about 120 km from the capital, left the city with a few seconds at most because the epicentre was so much closer than the coast. See recent earthquakes in Mexico.

Taiwan, South Korea, Israel, Canada, Romania and China

Taiwan pairs its dense network with cell broadcast: the Central Weather Administration’s alert reaches every phone on the island within seconds, and the island’s frequent large offshore earthquakes, such as the April 2024 Hualien event, are exactly the case where it helps. Taiwan’s recent earthquakes show how active the setting is. South Korea built its system after the 2016 Gyeongju earthquake surprised a country that had assumed it was safe. Israel’s TRUAA became operational in 2022 and is designed for the Dead Sea Transform, delivering through the same national alert app used for other emergencies.

Canada launched public earthquake early warning in 2024, first in British Columbia and then in Ontario and Quebec, using the existing Alert Ready emergency channel. Romania’s system is a special case: the deep Vrancea earthquakes lie about 150 km from Bucharest, so the capital can be warned even though the source is onshore, and the system mainly serves institutional users. China has been building a national system for several years and delivers alerts through phone makers and television in the provinces already covered.

Google’s Android Earthquake Alerts

Where there is no government network, the most widely available early warning is the one Google runs on Android phones. The Android Earthquake Alerts System launched in California in August 2020 using ShakeAlert data, then expanded to use the accelerometers inside Android phones as a distributed sensor network. When many phones in an area detect shaking at the same moment, Google’s servers estimate an epicentre and magnitude and alert phones farther out. It now operates in around 98 countries, including Spain, Greece, New Zealand, Turkey, the Philippines, Indonesia and most of Latin America.

It uses two levels. A Be Aware alert is sent for expected light shaking from an earthquake of magnitude 4.5 or more and behaves like a normal notification. A Take Action alert is sent for expected moderate or stronger shaking, bypasses Do Not Disturb, fills the screen and plays a loud sound. It is not as fast or as complete as a dedicated network, and Google says alerts may occasionally arrive late, be missed or overestimate shaking, but for most of the world it is the only early warning that exists.

Countries with no public system

The list of countries without earthquake early warning is longer than the list with it, and it includes some of the most seismically exposed places on earth. Spain has no public system: the Instituto Geográfico Nacional publishes events within minutes, but nothing warns before the shaking. The same is true of Italy, Greece, Turkey, Iran, Nepal, Indonesia, the Philippines, Chile, Peru, Colombia and New Zealand, where research systems exist or Android alerts operate but no national service warns the public before strong shaking. Peru began deploying a national system, SASPe, in the 2020s and Chile, Italy and Turkey have all evaluated one. Where you live decides what you can get: check the early-warning line on any of our region pages, for example Spain, Chile or Indonesia.

How many seconds you get

The honest answer is: it depends almost entirely on your distance from the epicentre, and the people who most need a warning get the least. The gap between P-wave and S-wave grows by roughly 1.2 seconds for every 10 km, and a system spends the first several seconds of that gap detecting and deciding. In round numbers:

• Inside about 25 km: no usable warning. This is the blind zone, and for a moderate crustal earthquake it contains most of the damage.
• 50 to 100 km: a few seconds. Enough to drop, cover and hold on, to stop a train, or to step away from a window.
• 150 to 300 km: ten to thirty seconds. This is the regime SASMEX and Japan’s coastal alerts were built for, and it is why offshore subduction earthquakes are the systems’ best case.

Every system also trades speed against accuracy. Alert early and the magnitude estimate is rough, so some alerts are false or overstated; wait for certainty and the blind zone grows. Different countries set the balance differently, which is why Japan’s public alert is rare and loud while Google’s Be Aware alert is common and quiet.

Getting the alerts on your phone

You almost never need to install anything. Government cell broadcast reaches every compatible phone in the area as long as emergency alerts are enabled, and Android phones receive Google’s alerts as long as the earthquake-alerts setting is on. The step-by-step settings are in our guides for Android and iPhone and iOS.

Frequently asked questions

Sources and further reading

• USGS: earthquake early warning overview
• USGS: ShakeAlert earthquake early-warning system
• USGS: the blind zone of earthquake early warning
• Japan Meteorological Agency: Earthquake Early Warning
• CIRES: Sistema de Alerta Sísmica Mexicano (SASMEX)
• Central Weather Administration, Taiwan
• Natural Resources Canada: Earthquake Early Warning
• Google: Android Earthquake Alerts System
• MyShake, the ShakeAlert delivery app operated by UC Berkeley