Evidence for Synchronization in the Global Earthquake Catalog

Phase alignment (synchronization) is a generalized property of interacting oscillators. If such interactions apply to earthquakes, they should manifest as time-dependent variations in earthquake productivity organized according to a characteristic elastic loading period. Defining this period as renewal interval, the time required to accumulate the elastic potential energy released in a rupture, gives a consistent scaling property that can be used to search for temporal organization. We test for the expected structure in earthquake productivity using three different statistical tools optimized for different temporal sensitivities: Schuster spectra for events with short renewal intervals (0-25 years), Fourier power spectra for events with short and intermediate renewal intervals (0-100 years), and topological data analysis (TDA) for events with long renewal intervals (>100 years). All three indicate that earthquakes are organized in time according to renewal interval. Accounting for such unsteady temporal organization may improve forecasting skill by providing time-dependent event probabilities. Plain Language Summary Earthquakes can be thought of as elastic objects that store potential energy as they are loaded over time by tectonics and then release that stored energy during rupture. This loading and unloading cycle defines a characteristic timescale for an earthquake, its renewal interval. Generalized systems of many objects of this type are known to have nonlinear interactions over many cycles of loading and unloading that lead to patterns of events in time, such that events with similar natural periods become synchronized. We test for these interactions in earthquakes by sorting the global earthquake catalog by renewal interval and then testing whether events with similar renewal intervals tend to occur closer together in time than would be expected for independent event occurrence.