Synthetic earthquake rupture models as an aid in interpreting geological data, Bull. To appear in the December Issue. Observations of large earthquake ruptures, unfortunately, are always going to be spotty in space and time and I believe that the extent to which such information succeeds in contributing to a grander view of earthquakes is going to be borne not only by the quantity and quality of data collected, but also by the means by which it is interpreted. This paper addresses the need to more fully understand geological data through carefully tailored computer simulations of fault system ruptures. Dogtails and rainbows are two types of fault rupture terminations that can be recognized in the field and can be interpreted through these models.
Rainbows are concave down ruptures that indicate complete stress drop and characteristic slip.
Rainbow terminations usually coincide with fault ends or strong segment boundaries. Dogtails are concave up ruptures that indicate incomplete stress drop or stress increase and non-characteristic slip. Dogtail terminations can happen anywhere along a fault or fault segment. The dogtail implies that the displacement observed in the 1979 quake is not characteristic. Although the segmentation and strength of the Imperial fault are well constrained, modest changes in two friction law parameters produce several plausible histories.