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Withdrawn: Quantitative Lacustrine Paleoseismology May Reveal the Rupture Direction of the 1717 CE Alpine Fault Earthquake.

The spatial distribution of earthquake ground shaking is controlled by the location, magnitude and rupture direction of an earthquake. Paleoseismic investigation can provide invaluable information on the location and magnitude of prehistoric large earthquakes but reconstruction of rupture direction has proved challenging. Recent work comparing the spatial distribution of ground motions to turbidite emplacement associated with the 2016 M_w7.8 Kaikōura earthquake has shown that turbidite paleoseismology may provide a tool for reconstructing rupture direction. Here we use a network of seven lakes throughout the northern South Island of New Zealand to constrain the spatial distribution of ground motions and rupture direction of the most recent M_w>8.0 earthquake on the Alpine Fault that occurred in ~1717 CE. Precise chronologies developed from a combination of ²¹⁰Pb, biostratigraphic and ¹⁴C dating were used to identify the sedimentary signatures (ranging from in-situ deformation structures to deposits resulting from subaqueous mass-wasting and earthquake-related processes in the lake catchments) of historic earthquakes in the lakes to constrain the relationship between ground motions and the observed earthquake signatures. These calibrations were used to reconstruct the spatial distribution of ground motions associated with the 1717 CE Alpine Fault earthquake by identifying deposits formed by this earthquake using the precise chronologies and assigning ground motions based on the type of sedimentary signature associated with the earthquake. Preliminary comparison of the reconstructed spatial distribution of ground motions and physics-based ground motion simulations that account for rupture direction show that the 1717 CE rupture most likely had a south to north rupture direction. Ongoing work aims to establish whether the Alpine Fault has a preferential rupture direction by examining the shaking distributions of preceding earthquakes. Our work shows the potential of lacustrine paleoseismology for reconstructing the location, magnitude and now rupture direction of past earthquakes.

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Presentation Time: Pacific

Presenting Author: Jamie D. Howarth

Student Presenter: No

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