Comparative study of tectonic tremor locations: Characterization of slow earthquakes in Guerrero, Mexico

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 40km 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 5km deeper than the established plate interface. The slip directions of the VLF events are slightly (similar to 10 degrees) 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.