Paleoearthquakes at Earth's surface often generate faults with variable displacement rates over short time intervals (e.g., <18 k.y.). The nature and origin of these variations and the extent to which they result from systematic, and therefore predictable, earthquake processes is unresolved. We examine the processes underlying fluctuations in displacement rates by charting the accumulation of displacement over the last 60 k.y. on 25 normal fault traces distributed across the Taupo Rift, New Zealand. Displacement rates become more stable with increasing fault size and are uniform when aggregated across the entire rift. The increased stability of fault displacement rates at greater spatial scales suggests that each fault is a component of a kinematically coherent system in which all faults interact and their earthquake histories are interdependent. Fault interdependencies generate short-term complex (<18 k.y.) fluctuations in the timing and magnitude of earthquakes, but also ultimately result in the stability of displacement rates on million-year time scales.