Fig. 2

An example of digitization result. Comparison of the original (top) and digitized (bottom, snapshot of the SAC window view) long-period north–south seismogram containing seismic wave arrivals. Note that the x- and y-axes do not quite match for the two plots, although the SAC display has been stretched/shrunk to mimic the original image. The numbers “45” and “50” on the original image correspond to 21:45 and 21:50 on September 21, 1939. The seismic wave arrivals are associated with a magnitude 5.8 earthquake in the Gulf of California (International Seismological Centre 2022)