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Earthquake Early Warning

Earthquake early warning (EEW) detects an earthquake after it begins and attempts to notify locations before damaging shaking reaches them. It is not earthquake prediction.

Why warning can be possible​

Seismic waves travel through the Earth much more slowly than electronic messages. A system can detect early arrivals, estimate the event and expected shaking, and distribute a message while stronger waves are still traveling toward more distant locations.

Earthquake begins
      ↓
Stations detect initial motion
      ↓
Processing associates observations and estimates the event
      ↓
Expected shaking is evaluated for target locations
      ↓
Alerts are distributed
      ↓
Strong shaking reaches locations that are far enough away

Every step consumes time. Warning time depends on the earthquake, station geometry, detection thresholds, processing, communications, alert policy, and recipient's distance from the source. A fixed table of warning time by epicentral distance is misleading because depth, wave speeds, network layout, and latency vary.

Blind zone​

Locations close to the source can experience strong shaking before the system has enough observations to issue a useful alert. No network density or communications technology eliminates this blind zone completely.

Blind zone and warning timedistance from epicentretime after the earthquake startsstrong shaking arrivesalert sentblind zoneshaking before the alertwarning time
Near the epicentre, shaking arrives before an alert can go out. Farther away, the gap between the alert and the strong shaking grows.

Initial estimates change​

The earliest data represent only the beginning of a rupture. Automated estimates can change as:

  • More stations detect the event
  • The rupture grows
  • Noisy or incorrect picks are rejected
  • Magnitude calculations receive longer waveform windows

Alert design must account for late, missed, false, and updated messages. Automated actions should be based on an engineering risk assessment, not only a magnitude threshold.

Components of an EEW service​

Detection network​

Stations require suitable geometry, low enough noise, accurate timing, reliable telemetry, and known metadata.

Processing​

The system identifies candidate arrivals, associates stations, estimates source parameters, predicts expected shaking, and decides whether alert criteria are met.

Alert delivery​

Messages may be delivered through public warning channels, applications, sirens, or direct machine interfaces. Delivery latency and availability must be measured end to end.

Prepared response​

A warning is useful only when recipients know what to do. Procedures, training, accessibility, testing, and fallback behavior are part of the system.

Appropriate actions​

Depending on jurisdiction and engineering review, warnings can support actions such as prompting people to Drop, Cover, and Hold On or placing controlled systems into a safer state. Automatic control of trains, utilities, industrial processes, elevators, or medical systems requires specialist design, fail-safe behavior, and approval from the responsible operators.

Earthquake detection in Grillo Cloud​

Grillo sensors provide observations to a network. On the Seismic and Enterprise plans, Grillo Cloud turns those observations into automatic event information and shows detections on a live map for your team. It is not a public warning service: delivering alerts to the public needs its own delivery channels, governance, and testing.

Do not present a sensor installation as an operational EEW system until the complete detection, alerting, governance, and response chain has been validated.

Further reading​