Events

Why earthquakes happen where they do

The Earth's outer shell is broken into large pieces called tectonic plates, which move a few centimetres a year, about as fast as fingernails grow. Where plates push together, pull apart or slide past each other, rock bends until it suddenly breaks and slips. That sudden slip is an earthquake. This is why most earthquakes line up along plate edges, such as the 'Ring of Fire' around the Pacific, which includes Taiwan and Japan.

Reading the magnitude

Magnitude measures the size of an earthquake on a logarithmic scale. Each step up means about 10 times bigger ground motion on a seismograph and about 32 times more energy: a magnitude 6 releases about 32 times more energy than a 5, and about 1,000 times more than a 4. Depth matters too: a shallow earthquake shakes the surface much harder than a deep one of the same magnitude.

Alerts

Set a radius around your favourite places and your location, a minimum magnitude and a minimum severity, and the app tells you when something matching happens. Alerts appear while the app is open.

What the toggles show

Volcanoes

Shows volcanoes from NOAA's catalogue as triangles, coloured by the last eruption it records: red since 1964, orange from 1900 to 1963, grey older or unknown. Tap one for its type, height or depth, and last eruption.

Depth

Colours each earthquake by its depth: red for shallow (less than 70 km), yellow for intermediate (70 to 300 km), blue for deep (more than 300 km). Deep earthquakes trace plates sinking into the mantle.