Modelling subduction sources for probabilistic seismic hazard analysis

Abstract Subduction zones are highly productive seismic sources both at the interface and within the slab, and have produced many of the highest-impact earthquakes throughout history. Several current probabilistic seismic hazard analyses model interface sources as faults with rates constrained by only seismicity or tectonics singularly, and intraslab sources as gridded points, sometimes smoothing rates according to former occurrences. Here, we propose a subduction source modelling methodology that improves on current standards for both source types. We use cross-sections of earthquake catalogues, focal mechanisms and geophysical models to define the locked subduction interface and slab volume, and to classify seismicity. We divide these geometries along-strike to impose segment boundaries. For the interface, we combine tectonic and seismicity components to assign occurrence properties, considering fault area, convergence rate and seismic coupling. We use ruptures that are confined to the slab volume to demarcate intraslab sources, enhancing their utility with ground motion prediction equations that use site-to-rupture distance. We demonstrate the proposed approach on the Nazca subduction zone of South America, validating the source model parameters against observed earthquakes and palaeoseismic information when available, and showing that the resulting magnitude–frequency distributions better fit the observed occurrences than traditional approaches.