Map showing the seismicity in the vicinity of Yellowstone and the eastern Snake River Plain. Three colors represent the respective positions of the seismic parabola as assessed by several authors. Note that is an interior parabola that defines a zone of aseismicity called the collapse shadow (Anders, 1983). The pattern defined by Pierce and Morgan (1992) is based primarily on the location of active normal faults whereas the two parabolas defined by Anders et al. (1989) are based solely on the distribution of seismicity.