Periodicity and Clustering in the Long-term Earthquake Record

Instrumentally observed earthquakes sequences typically show clusters of earthquakes interspersed with periods of quiescence. These ‘bursty’ sequences also have correlated inter-event times (‘long-term memory’). In contrast, elastic rebound theory forms the basis of the standard earthquake cycle model, and predicts large earthquakes to occur regularly through cycles of strain accumulation and release (periodicity). In this model the conditional probability of future large earthquakes is reduced immediately following fault rupture, and inter-event times are independent. Here we use the burstiness and memory coefficient metrics to characterize more than 100 long-term earthquake records. We find that large earthquake occurrence on the majority of Earth’s faults is weakly periodic and does not exhibit long-term memory; earthquakes occur more regularly than a random Poisson process although inter-event times are variable. In contrast, clustering occurs in slowly deforming regions (annual rates < 2 x 10-4), and is not explained by elastic rebound theory. Citation: Griffin, J. D., Stirling, M. W., & Wang, T. (2020). Periodicity and clustering in the long‐term earthquake record. Geophysical Research Letters, 47, e2020GL089272. https://doi.org/10.1029/2020GL089272