Activity

Every cell is one hour, coloured by how much the ground was moving — the median of that hour’s four helicorder intervals. Pale blue is quiet, deep red is busy, and the colour also darkens the whole way, so the picture survives being printed or read by a colourblind eye. Times are local, not UTC, because this chart is about people: indexed by UTC the morning rush would land in the middle of the night.

Almost everything here is human. The quiet band across the small hours is the neighbourhood asleep; it lifts around 05:00, runs loud through the working day, and falls away again after dark. Roughly a 4× swing between 4 AM and mid-afternoon, and none of it is geology. That is also why this station detects smaller earthquakes at night — the same quake has to compete with four times less noise.

Collapsing every hour onto one week is the better portrait — it averages out one-off events and shows the weekday/weekend difference. It needs 14 days of settled configuration and the station has 13.5 since the last change on 12 August. This card fills itself in around 26 August, assuming nothing else is rebuilt before then.