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

234 PATA Days 2024 Scarps of the Hill Top Fault show variable west and east side up displacements, consistent with typical surface expression for a strike- slip fault. In many locations several sub-parallel scarps are present, suggesting a complicated structure. The fault primarily offsets Silurian aged bedrock, making measurements of total neotectonic displacement difficult to determine. However, scarps are also present across presumed Quaternary-age sediments (Figure 5), providing evidence for the fault being active in the current stress regime. R E S U LT S The four trenches on the Jindabyne Thrust all exposed evidence for multiple paleoearthquakes. In all trenches, weathered Silurian granodiorite was observed to have been thrust over Quaternary sediments. Trench C1 presented clear evidence of at least three past earthquakes (Figure 6). The scarp height (~10 m), the presence of sediments below the colluvial deposit associated with the ante-penultimate event, and a thick (>0.5 m) fault gouge zone all provide evidence for additional events prior to the most recent three. The lower two trenches on the alluvial fan (F2 and F3) contain evidence for two paleoearthquakes while the upper fan trench (F1) contains evidence of at least three paleoearthquakes. Fig. 6: Part of the north wall of trench C1 a) uninterpreted; and b) interpreted geology around the main fault zone, showing multiple slip planes, thick fault gouge and three faulted colluvial deposits associated with past earthquakes. Ages from single-grain optically stimulated luminescence (OSL) indicate a most recent event in trench F1 to between 10.9 ± 1.5 ka and 2.6 ± 0.4 ka (1 sigma uncertainty; assuming Central Dose Model) or to between 4.7 ± 0.7 ka and 0.73 ± 0.19 ka (1 sigma uncertainty; assuming Minimum Dose Model). Preliminary ages (derived from only a small number of grains, and hence presented without quantified uncertainties) for unfaulted sediments in trenches F2 and F3 are 4 – 5 ka. Assuming the most recent event ruptured all three traces, an early to mid-Holocene age is indicated. These ages confirm the first Holocene paleoearthquake rupture identified in a trench in Australia. Additional dates from trench F1 provide an age of ~37 ka for sediments at the base of the footwall trench exposure, constraining the time interval in which the three paleoearthquakes occurred. Combining available ages from trenches F1 and F3, an ante- penultimate event likely occurred between ~37 and 28.7 ± 2.3 ka, and a penultimate event between 28.7 ± 2.3 ka and 16.5 ± 2.0 ka.