co·seis·mal 
(kō-sīzməl, -sīs-) also co·seis·mic (-mĭk)
(kō-sīzməl, -sīs-) also co·seis·mic (-mĭk)adj.
Relating to or designating a line connecting the points on a map that indicate the places simultaneously affected by an earthquake shock.
n.
A coseismal line.