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

248 PATA Days 2024 Fig. 4: Example of curved slickenlines on the Kekerengu Fault. (A) Stereonet plot of the orientation of slickenlines from this study (orange) and slickenlines from free faces of the 2016 Kaikōura earthquake (red). (B and C) photographs of slickenlines from the 2016 earthquake. (D) photograph of slickenlines exhumed during this study. R E F E R E N C E S Kearse, J., Y. Kaneko, T. Little, R. Van Dissen, (2019). Curved slickenlines preserve the direction of earthquake rupture propagation. Geology 47 (9), 838-842. Kearse, J., Y. Kaneko, (2020) On- fault geological fingerprint of earthquake rupture direction. Journal of Geophysical Research: Solid Earth 125 (9), e2020JB019863. D I S C U S S I O N A N D C O N C L U S I O N S We have presented a new approach to fault trenching to preserve, expose, and document slickenlines. In our trenching investigations we find that excavator- assisted removal of near-faultmaterialwas successful in preserving the fault plane. By carefully exposing fault surfaces using hand tools we were able to preserve and document slickenlines without removing or disturbing them. Slickenline observations were gathered by incrementally exposing small 25 x 25 cmwindows of fault surface. Our new slickenline observations from the Kekerengu Fault align with other observations of slickenlines from global historical earthquakes, and together show that coseismically-inscribed curved slickenlines are both widespread and typical. Our excavations of the Kekerengu Fault revealed slickenlines of the same sense of convexity as those found on free faces following the 2016 Kaikōura earthquake; this sense of convexity is consistent with the observed and modelled northeast-directed rupture propagation during the 2016 earthquake. The agreement between both datasets demonstrates that both the kinematics and the dynamic motion of the Kekerengu fault during the 2016 earthquake are preserved in the geological record on the Kekerengu fault plane at shallow depth. Based on this research, we infer that shallow excavations can be used to constrain the rupture direction of recent large paleoearthquakes on faults worldwide. We suggest that this approach can be used to fill a knowledge gap regarding the rupture direction of paleoearthquakes on faults that lack historical surface rupturing earthquakes. This is potentially a big advance towards better characterization of earthquake ground shaking hazard. A C K N O W L E D G E M E N T S This research is supported by the Royal Society of New Zealand Marsden Fund (20-GNS-006; PI: Van Dissen; additional collaborators: Y. Kaneko, J. Howarth, C. Orchiston).