Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

(2020) that suggests that the curvature of slickenlines can record the direction of earthquake rupture propagation. Kearse and Kaneko (2020) use dynamic rupture models to show that in the shallow subsurface, the trajectory of slip is expected to follow a curvilinear path, and that the sense of this curvature should be opposite at either end of a propagating earthquake rupture. In this way, they demonstrate that the sense of convexity can indicate the direction of earthquake rupture. To evaluate this theory, they compare the curvature (or inferred curvature) of geologically observed slickenline tracks formed during 8 historical earthquakes with model-predicted curvature, and found that for each event the models and the observations agreed. To further test whether this theory can be applied to the study of paleoearthquake ruptures, we have un-earthed and documented curved slickenlines on the Kekerengu Fault (New Zealand), which last slipped during the 2016 Kaikōura earthquake (Fig. 1). This rupture had a northeast propagation direction, and slickenlines observed immediately after the earthquake on free faces had consistent senses of curvature consistent with the known propagation direction (Fig. 2). In the current study, we use this fault to test a new type of paleoseismic trenching approach that focuses on the exposure and documentation of buried slickenlines, be they historic or prehistoric. In a complementary study (Barth et al., these proceedings) we demonstrate how to modify natural fault exposures using hand tools to successfully un-earth and document paleoslickenlines on the plate boundary Alpine Fault. Fig. 1: Map of the 2016 rupture of the Kekerengu Fault (red) showing the locations of the 2023 trench sites where the data for this study were collected. Post-earthquake slickenline observations were available from the northern two sites (Glencoe Stream, Sawtooth Run) whereas no slickenlines were documented in post-earthquake reconnaissance at Shag Bend.