The low-frequency earthquake / Non-volcanic tremor system

We use data from the MesoAmerican Subduction Experiment to detect and locate low-frequency earthquakes (LFEs) in the Mexican subduction zone. We develop an algorithm that automatically detects LFEs based on network signal coherency. These detected LFEs are then used as templates in a matched-filter search; the group of LFEs found with a given template is considered a family of LFEs. Stacking the waveforms of all of the family's LFEs results in seismograms with clear P- and S-wave arrivals; these travel times are then used to locate the sources. The locations superpose a region of permanent NVT activity. The LFE family hypocenters have been located at a depth of 40 - 45 km in an area that is surrounding the upper slab-plate interface. We characterize their focal mechanisms by comparing their stacked seismograms to synthetic seismograms with varying moment tensors revealing a common low-dipping thrusting focal mechanism that reflects the subduction geometry. Recurrence interval analysis of the resulting LFE catalog reveals a steady background event rate underlying a non-periodic burst-like behavior. We develop a simple algorithm to generate a catalog of LFE bursts, separating the events that occur within bursts from the background events. We observe that the bursts of individual LFE families do not exhibit any characteristic recurrence interval and appear memory-less; however, using the entire catalog of all LFE families, the entire source region does exhibit a characteristic burst recurrence interval, suggesting interaction between individual LFE families.