Isochron 2
Isochron 2 : In seismology, a line on a map or a chart connecting points of equal time or time interval, e.g., arrival times of the onset of seismic waves from a source. In geochronology, a line connecting points of equal age. In marine geophysics, the magnetic lineation with equal age, often abbreviated as chron. See Cox (1973), Uyeda (1978), and Duff (1993)