Calibrating the marine turbidite palaeoseismometer using the 2016 Kaikōura earthquake

Turbidite palaeoseismology has produced arguably the most comprehensive multimillennial scale records of subduction-zone earthquakes but is underpinned by techniques that are vigorously debated in earthquake science. Resolving this argument requires new direct observations that test the approach’s essential assumptions. Here we present measurements from turbidites triggered by the 2016 Mw 7.8 Kaikōura earthquake in New Zealand, one of the most well-instrumented earthquakes in history. This natural experiment provides an ideal test for turbidite palaeoseismology because fault source, ground motions and turbidite deposition in discrete canyons are well-resolved by analysis of sediment cores combined with physics-based ground-motion modelling. We find that the Kaikōura earthquake triggered flows in ten consecutive canyon–distributary systems along a 200 km segment of the Hikurangi subduction margin where long-period (>2 s) peak ground velocities exceeded turbidity-current-triggering thresholds between 16–25 cm s−1. Comparison between ground motions and turbidite deposition confirm that there is a predictable relationship between earthquake source, ground motions and deposition of coseismic turbidites. We demonstrate that the patterns of triggering and resultant turbidite character may preserve evidence of fault-rupture direction along with the radiating patterns and amplification of earthquake ground motions. Marine turbidite deposition is confirmed to relate to earthquake ground motions by an analysis of turbidite deposits and simulations of ground motions from the 2016 Kaikōura earthquake.