coseismal adjective 1noun 1forms 1 adjective1 •Of or pertaining to a line on a map connecting places simultaneously affected by a seismic event. noun1 •A line on a map connecting places simultaneously affected by a seismic event.Now, the average distance between the two inner coseismals is 32 3/4 miles, between the two outer ones (so far as drawn) 35 1/6 miles, and between the first and third 67 1/6 miles. — 2013 formscoseismals
