How Far Did the Kumamoto Earthquake Travel?

About This Chart

Data Visualization Method

• Data: Official per-station seismic intensities from the Japan Meteorological Agency for the 28 July 2026 Kumamoto mainshock. Station readings are observed; grid values are interpolated from them.
• Moment and area: A single mainshock (16:27 local time, Mj 7.1, depth ~10 km), shown over an animated timeline across Japanese land.
• Selection: Of 1,058 station records, the 1,050 with both a numeric intensity level and coordinates were used. Four "not yet received" records and four stations without matched coordinates were excluded.
• Processing: A ~5 km land grid, each cell interpolated by inverse-distance weighting of its 12 nearest stations — held to about 20 km, then tapered from 20 to 65 km. Sparse cells were dropped and an isolated distant station was kept to a small local footprint.
• Chart form: An animated point map. Color encodes interpolated intensity; two thin rings expanding from the epicenter stand for the P and S waves.

Creator's Note

The aim was to set human perception aside and ask a narrower question: where, and in what shape, did instruments actually record the shaking? Rather than reducing the event to a single magnitude number, it places the observed intensities on one comparable surface.

What stands out is that the shaking did not radiate as a clean circle. It concentrates near the epicenter and fades along the shape of the archipelago toward the northeast — a reading of distribution, not a ranking of places.

Data Sources

• Japan Meteorological Agency — Seismic Intensity Stations — official station intensities and coordinates used for the grid.

Limitations

Each grid color is an interpolated estimate from surrounding stations, not a direct measurement at that spot. The official values belong to the stations themselves; cells with almost no nearby observations were left out, and a lone distant station was handled locally so it would not spread into a wide patch.

The two rings are an editorial layer that conveys the direction and order in which the shaking unfolded — not real per-station arrival times or wave speeds. The color and point-size inputs are chosen for legibility, not as physical units of energy or acceleration.

A maximum intensity of 7 is a peak at particular sites, not a nationwide figure. Open sea and areas outside Japan fall outside this grid, and the softened northeastern edge is a deliberate choice to avoid cutting the observation boundary with a hard line. This is a map of recorded shaking, not of damage or casualties.