Low-frequency earthquakes in the Mexican sweet spot

Abstract

We use data from the Meso?America Subduction Experiment to detect and locate low?frequency earthquakes (LFEs) in the Mexican subduction zone. We use visually?identified templates to perform a network waveform correlation search that produced ~17,000 robustly detected LFEs that form 15 distinct families. Stacking an LFE family's corresponding detections results in seismograms with high signal?to?noise ratios and clear P and S wave arrivals; we use these travel times to locate the sources. The resulting locations superpose a previously identified region of permanent non?volcanic tremor (NVT) activity. Husker et al. (2012) called this region a Sweet Spot, suggesting that the local conditions are adequate to continuously generate NVT. The LFE 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. This analysis reveals a common low?dipping focal mechanism.