Travel-Time Curve

a curve describing the relation between the travel time of a seismic wave and the epicentral distance; it may be expressed in tabular or graphic form. Traveltime curves are used to determine the propagation velocity of seismic waves in the earth. A sharp change in the velocities of seismic waves indicates the existence of boundary surfaces (interfaces) within the earth. H. Jeffreys and K. E. Bullen’s traveltime curves (1940) are based on a standard model of the earth with boundary surfaces corresponding to the crust, mantle, and core. They are used in modern seismology to determine the position of earthquake foci. Regional travel-time curves account for local characteristics of regional structure and are used to interpret weak and nearby earthquakes.