New Nature Communications publication on unraveling the riddles of the 2016 Kaikōura, New Zealand earthquake

Surprising insights on the 2016 Magnitude 7.8 Kaikoura, New Zealand earthquake, one of the most puzzling and well recorded earthquakes ever, are gained from earthquake models of unprecedented degree of realism now published in Nature Communication. The Kaikōura earthquake posed scientists many riddles giving rise to speculation. The event did not break the suspected faults and stopped unexpectedly - why? At the surface, some ruptured faults are far apart. Were there hidden fault connections at depth? On average, the rupture was slow. Is this the effect of a tortuous rupture path? The earthquake induced a much higher than expected tsunami, the biggest in the region since 1947. Was this caused by a rare occurrence of an earthquake starting on-land and crossing to numerous faults off-shore? What was the role, if any, played by the Hikurangi subduction interface, situated below the network of crustal faults apparent at the surface? Previous studies of the Kaikōura earthquake based on geological, geodetic, tsunami and seismic data led to competing hypotheses to answer to these questions. Geophysicists from LMU Munich, Université Côte d’Azur and the Hong Kong Polytechnic University collaboratively used high-quality observations to inform an earthquake simulation done on the Supercomputer SuperMUC in Garching, Germany. Importantly, the model incorporates the physics of how rocks below Earth’s surface break suddenly, producing seismic waves and shaking the ground. The researchers find, that the cascading earthquake’s riddles can be resolved assuming a very low resistance of the complex fault system caused by combined weakening mechanisms: silent creep of deeper parts of the faults over thousands of years, fluids under high pressure surrounding the fault and rapid frictional weakening during the event. Thomas Ulrich, lead author and PhD student at the Geophysics Institute of the Department of Earth and Environmental Sciences at LMU Munich, states: “Earthquake modeling is now approaching a state of maturity and computational efficiency that will soon make it an important part of the rapid earthquake response toolset, by delivering physics-driven interpretations that can be integrated synergistically with established data-driven efforts within the first days after an earthquake.” Reference: Dynamic viability of the 2016 Mw 7.8 Kaikōura earthquake cascade on weak crustal faults, T. Ulrich, A.-A. Gabriel, J.-P. Ampuero, W. Xu, Nature Communications, doi:10.1038/s41467-019-09125-w, 2019.