High-resolution relocation of intraslab earthquakes beneath South America using global seismic data

The accurate location of intermediate-depth earthquakes has proven to be one of the more enduring problems in global seismic location studies.  Complicated in many cases by a paucity of near-field observational data, the determination of accurate source depths for such earthquakes, in particular, has proven to be elusive.  As a result, and despite improvements in recorded seismic data density and quality, the distribution and controls of these events remain poorly understood.

Depth phases (near-source surface reflections, e.g. pP, sP, sS) are crucial for the accurate determination of earthquake source depth using global seismic data. However, such phases are often difficult to detect, suffering from low signal-to-noise ratios, are disguised in the direct-wave coda, and often suffer from an ambiguity as to which depth phase has been observed.  Here, we draw on the vast expansion of seismic network coverage over the last few decades to develop an approach using adaptive medium-aperture teleseismic arrays to boost the detection, identification, and inclusion of depth phases, for both P and S waves. Our approach leads to a radical increase in the number of depth phases detected, particularly for smaller-magnitude events, down to a magnitude of 4.7. We then assess how the inclusions of increased depth phase observations impacts on the resolution and accuracy of global earthquake location algorithms. 

Using data from 30 years of earthquakes along the length of the South American subduction zone, we show the potential for such array-based observation to enhance current global location routines, producing higher-resolution earthquakes catalogues capable of imaging the complex distribution of intraslab seismicity.  With this enhanced earthquake catalogue, fine-scale variations in intraslab seismicity are detectable, shedding light on the geodynamic processes behind such earthquakes.