Temporal Evolution of Seismicity in the Central Southern Alps, New Zealand: Evidence for Rainfall-Triggered Seismicity

Understanding the conditions and mechanisms that produce earthquakes is of high scientific relevance. The central Southern Alps/Ka Tiritiri o te Moana of New Zealand is an active orogen that offers a unique opportunity to study the processes that drive seismogenesis. A new high-quality, matched-filter-based microseismicity catalog has been constructed by following a fully automated detection and location process. The catalog spans from 2009 to 2020 with local magnitudes between M-L -1.81 and 3.42. Our results indicate a seasonal pattern in earthquake occurrence, with a notable correlation between shallow-depth earthquakes (similar to 6 km hypocentral depths) and large, mostly summer, rainfall events beneath three separate glaciers. We hypothesize that a combination of seasonal snowmelt and heavy rainfall events raises the water table during spring and summer, changing pore-fluid pressure in the upper crust and triggering earthquakes. Our findings highlight the role of extreme rainfall and glacier dynamics in triggering shallow earthquakes, which can improve hazard assessment in the central Southern Alps/Ka Tiritiri o te Moana and similar alpine regions worldwide.