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Two example aftershock sequences, from southern California, that illustrate the three general rules of aftershocks. A circle shows each aftershock's time of occurrence (horizontal axis) and magnitude (vertical axis). The larger-magnitude M6.7 Northridge earthquake is followed by many more aftershocks than the smaller M5.1 La Habra earthquake. The rate of aftershocks in both sequences decreases as time passes. The magnitudes of the aftershocks don't change with time, meaning that large aftershocks are still possible later in the sequence, as happened following Northridge.