Figure 4.18. Age differences between equatorial Pacific calibration (defined as 0) and North Pacific age ranges. The horizontal bar represents the suggested calibration for the single events. The events are divided into three groups, from left to right: the first, largest group includes events that are older in the North Pacific than they are in the Equatorial Pacific, the second group of events is synchronous in the equatorial and North Pacific, the third group includes events that are younger in the North Pacific. The number of sites included in the age range is written below the bar (from Spencer-Cervato et al. 1993).