No abstract

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.

Slow earthquakes in Mexico have been investigated independently in different areas. Here we review differences in tremor behavior and slow slip events along the entire subduction zone to improve our understanding of its segmentation. Some similarities are observed between the Guerrero and Oaxaca areas. By combining our improved tremor detection capabilities with previous results, we suggest that there is no gap in tremor between Guerrero and Oaxaca. However, some differences between Michoacan and Guerrero are seen (e.g., SSE magnitude, tremor zone width, and tremor rate), suggesting that these two areas behave differently. Tremor initiation shows clear tidal sensitivity along the entire subduction zone. Tremor in Guerrero is sensitive to small tidal normal stress as well as shear stress, suggesting that the subduction plane may include local variations in dip. Estimation of the energy rate shows similar values along the subduction zone interface. The scaled tremor energy estimates are similar to those calculated in Nankai and Cascadia, suggesting a common mechanism. Along‐strike differences in slow deformation may be related to variations in the subduction interface that yield different geometrical and temperature profiles.

Deep tectonic tremor in Guerrero, Mexico, has been observed using dense temporal seismic networks (i.e., the Meso‐American Subduction Experiment and Guerrero Gap Experiment (G‐GAP) arrays) during two different time periods. We apply a set of seismic waveform analysis methods to these data sets to constrain the locations of tremors and determine the associated moment tensors. First we detect and locate the tremors. Next, very low frequency (VLF) signals are identified by stacking waveform data during tremor bursts, and their moment tensors are determined. Finally, to better investigate the link between tremors and VLF earthquakes, we detect VLF events using a matched filtering algorithm to search continuous seismic records. None of the 11 VLF events detected by this method occurred in the absence of tremor bursts suggesting they are indeed part of the same phenomena. Unlike previous investigations, our results for the G‐GAP period reveal that downdip tremor activity (i.e., in the so‐called “sweet spot”) is segmented into two patches separated by 40 km in the along‐trench direction, indicating possible variations in the geometry of the plate interface and/or slab effective pressure. Moment tensors of VLF signals are consistent with shear slip on the near‐horizontal plate interface, but source depths are about 5 km deeper than the established plate interface. The slip directions of the VLF events are slightly (~10°) counterclockwise of the plate convergence direction, indicating that strain energy promoting left‐lateral strike‐slip motion may accumulate in the continental crust during the interseismic period.