They say a picture paints a thousand words. This is a screenshot of the NZ Geonet quake drum in McQueen’s Valley.
This image represents ONE day’s recordings from the quake drum closest to Christchurch. Here’s the explanation of what you’re seeing:
The timestamp shown at the top right of the seismograph drum shown below is the time when this image was last refreshed. Each horizontal line (or trace) represents 30 minutes, each vertical line is spaced 1 minute apart; 24 hours of recording are displayed in total. The most recent signal is drawn at the bottom right hand corner of the drum. Then read the traces from right to left, bottom to top, to get from the most recent to the oldest signals. The trace will appear red if the signals are very large; this means they have been clipped to stop them overwriting too much of the surrounding image. The scale auto-adjusts to give the clearest view of the bigger earthquakes when the ambient conditions are noisy due to bad weather, frequent small earthquakes or nearby human activity.
I tried to count the spikes – too many; then I tried to count the ones with red – I think there’s 23 of them!
Kia Kaha Christchurch.