Fig. 7
From: DigitSeis: software to extract time series from analogue seismograms
Curvature introduced by pen-type recording system. Comparison of a raw seismogram showing the beginning of surface-wave arrivals at station HRV from the November 30, 2018, Anchorage earthquake (cyan line), and a version with curvature as would be generated by a pen-type system introduced (red line). The pen (pencil in the figure) swings around a pivot point, making arcs for large-amplitude arrivals, even though for small-amplitude arrivals, the cyan and red lines are practically identical