Figure  2 reviews the known historic seismicity of the region with Io ≥ 5.

Since it is a problem to locate epicenters accurately with only macroseismic data, Fig.  2 includes the range of uncertainty.

The series in Altdorf (1774, 10 known events) as well as two earlier series near Sarnen (1777, 11 known events but a contemporary observer speaks of 60 felt shocks, and 19 events in 1917) show a pattern similar to that of 1964 (Fig.  2 and Gisler et al.