Spatiotemporal patterns of earthquakes and their implications for earthquake hazards

[EMBARGOED UNTIL 5/1/2023] This work focuses on characterizing spatiotemporal patterns of earthquakes, their possible causes, and their implications for seismic hazard assessment. I studied both local and global earthquakes in the view of complex fault systems. Specifically, I studied the background seismicity and long-lived aftershock activities in intraplate North China and the Central and Eastern United State (CEUS), and characterized the correlation between strain rate and seismicity and evaluated the prediction power of strain rate in different tectonic settings. I found that periodic or quasiperiodic earthquake recurrence on individual faults, as predicted by the elastic rebound model, is not common in nature. Instead, most earthquake sequences are complex and variable, and often show clusters of events separated by long but irregular intervals of quiescence. The common earthquake clustering may be caused by earthquake-induced viscoelastic relaxation and fault interaction. Most earthquake sequences are burstier than the Poisson model, implying a higher probability of repeating events soon after a large earthquake. Possible long-lived aftershocks are found in intraplate North China and the CEUS. Background seismicity in intraplate regions may vary with time, highlighting the complexity of intraplate seismicity. Mistakenly identifying long-lived aftershocks as background earthquakes may overestimate seismic hazard in intraplate regions. The correlation between strain rate and seismicity varies between different tectonic settings and is time-dependent. Good strain rate-seismicity correlations are found in plate boundary regions and during seismically active periods, while no correlations are found in stable continents and during inactive periods. All these variations need to be considered in hazard assessment.