Seismic Moment, Seismic Energy, and Source Duration of Slow Earthquakes: Application of Brownian slow earthquake model to three major subduction zones

Tectonic tremors, low‐frequency earthquakes, very low‐frequency earthquakes, and slow slip events are all regarded as components of broadband slow earthquakes, which can be modeled as a stochastic process using Brownian motion. Here we show that the Brownian slow earthquake model provides theoretical relationships among the seismic moment, seismic energy, and source duration of slow earthquakes and that this model explains various estimates of these quantities in three major subduction zones: Japan, Cascadia, and Mexico. While the estimates for these three regions are similar at the seismological frequencies, the seismic moment rates are significantly different in the geodetic observation. This difference is ascribed to the difference in the characteristic times of the Brownian slow earthquake model, which is controlled by the width of the source area. We also show that the model can include non‐Gaussian fluctuations, which better explains recent findings of a near‐constant source duration for low‐frequency earthquake families. Plain Language Summary Slow earthquake is a group of strange earthquake‐like phenomena recently discovered in many subduction zones. It can be called by different names such as tectonic tremors, low‐frequency earthquakes, very low‐frequency earthquakes, and slow slip events, but actually considered as a very broadband phenomenon with various characteristic periods from ~0.1 s to ~1 year. This paper provides a theoretical model to explain various characteristics of slow earthquakes and compare the model with real observations in three major subduction zones: Japan, Cascadia, and Mexico. The interpretation of slow earthquake as a broadband phenomenon is essential for understanding the relation between earthquake rupture process and slow deformation in subduction zones. Key Points The Brownian slow earthquake (BSE) model provides theoretical relationships among seismic moment, seismic energy, and source duration These theoretical relationships are compared with observations of slow earthquakes in the Japan, Mexico, and Cascadia subduction zones A BSE model with a non‐Gaussian fluctuation can explain the observation of near‐constant duration in isolated low‐frequency earthquakes