#Earthquake Alerts

GlobalQuake includes a real-time alert system that monitors earthquakes and warns you when shaking may be expected at your home location. The system evaluates earthquakes against configurable distance and magnitude thresholds, estimates Peak Ground Acceleration (PGA), and displays severity-coded alerts with wave arrival countdowns.

#Alert Tiers

Alerts are color-coded by severity. When an earthquake meets alert conditions, the alert box appears at the bottom-center of the map with one of three colors:

The default threshold levels can be adjusted in Options > Settings > Alerts. You can use either the Modified Mercalli Intensity (MMI) scale or the Shindo scale (Japan Meteorological Agency).

#What You See

When an alert is active, the alert box displays the following information:

• Header bar — colored by the severity tier (blue, yellow, or orange).
• Max. Intensity — the estimated maximum intensity at your home location, shown as a Roman numeral level (e.g. "V") with the scale name (MMI or Shindo).
• Magnitude — the earthquake's magnitude (e.g. "M5.1").
• Distance — how far the epicenter is from your home location.
• Depth — the depth of the earthquake's hypocenter.
• P-wave countdown — a blue box showing the estimated time until the P-wave arrives (in seconds).
• S-wave countdown — a red box showing the estimated time until the S-wave arrives (in seconds).
• Flashing warning triangle icon — a visual indicator to draw your attention.

#Wave Countdown

The alert box includes countdowns for both P-waves and S-waves:

• P-wave (blue box) — the primary wave, which travels fastest but typically causes minimal damage. Arrives first.
• S-wave (red box) — the secondary wave, which is slower but carries more energy and is responsible for most shaking damage. Arrives after the P-wave.

The countdowns update in real-time as the earthquake's estimated location and timing are refined by the system. During the last 10 seconds before S-wave arrival, countdown.wav plays to alert you that shaking is imminent.

#Alert Sounds

GlobalQuake plays different sounds depending on what is happening:

#Configuring Alerts

All alert settings are managed in Options > Settings > Alerts. You can configure:

#Home Location

• Home Latitude / Home Longitude — set your approximate location for distance and PGA estimation.

#Intensity Scale

• Intensity Scale — choose between MMI (Modified Mercalli Intensity) or Shindo (Japan Meteorological Agency scale).

#Alert Thresholds

#Shaking Thresholds

#Other Options

#Alert Trigger Logic

The system evaluates each earthquake against the following conditions in order:

1. Local — within alertLocalDist (default: 200 km), regardless of magnitude.
2. Regional — within alertRegionDist (default: 1000 km) AND magnitude ≥ alertRegionMag (default: 3.5).
3. Global — magnitude ≥ alertGlobalMag (default: 6.0) OR felt-by population ≥ alertCountFelt OR strongly-felt population ≥ alertCountStronglyFelt.
4. Shaking expected — if the earthquake meets any of the above and the estimated PGA at your home location exceeds the configured shakingLevelIndex, the alert escalates to yellow or orange.