Assessing the impact of automatically derived depth phases on the determination of earthquake hypocentres – application to the South America subduction zone

Alice Blackwell, Timothy J Craig, Sebastian Rost, Thomas Garth, Ryan Gallacher

Accurate earthquake hypocentres are fundamental to a wide range of geophysical studies, yet source depth remains poorly constrained in teleseismic earthquake catalogues. Near source surface reflections such as pP, sP, and sS (known as depth phases) provide critical information for resolving hypocentral depth, particularly for intermediate-depth earthquakes. The number of depth phases reported by global earthquake monitoring agencies has declined significantly in recent decades, potentially reducing the precision of resolved earthquake depths. To address this, we automatically detect P, pP, sP, S and sS phase arrivals using teleseismic ad-hoc arrays. We detect these phases for earthquakes in the South American Subduction Zone (SASZ) at depths of 40–350 km and between mb 4.7 to 6.5. The identified phases are integrated with the phases reported to the ISC Bulletin, and used to relocate earthquakes with ISCloc. We assess the impact of incorporating automatically detected, ad-hoc array-derived depth phases on earthquake relocations across the SASZ, and find an improvement in depth resolution for 88.8% of earthquakes. Using this enhanced catalogue we investigate the structure of the Wadati-Benioff zone, focusing on two significant earthquakes: the 2005 Mw 7.7 Tarapacá and 2019 Mw 8.0 Peru events. Finally, we successfully apply our methodology to deep focus earthquakes (350-700 km), which further define the deepest portion of the seismogenic slab. Our results demonstrate the potential for automatically detected, ad-hoc array-derived depth phases to substantially improve the accuracy of teleseismic earthquake hypocentres, and offer further constraint upon slab geometry and seismogenic structure.