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

Although event timings are not tightly constrained by presently available OSL data, recurrence intervals appear to be on the order of 10 kyr. Further dating including cosmogenic radionuclides (CRN) will help to constrain these dates and recurrence. Single-event displacements measured in trench C1 provide minimum estimates due to erosion of the fault tip on the overthrust hanging wall. The measured single-event displacements exceed 1 m, which is only a portion of actual displacement. Combined scarp heights of ~2.5 m for the outboard two scarps excavated in trenches F2 and F3, which are interpreted to have formed by the two most recent events, suggest single-event displacements exceeding 2 m. Using scaling relations for shallowcrustal reversefaultdisplacements (Leonard, 2014; Yang et al., 2021) and assuming 2 m of displacement suggests a causative earthquake on the order ofMW~7.0. Considering fault dimensions, a complete rupture of the presently mapped Jindabyne Thrust would have a length of 100 km, suggesting a magnitude of MW ~ 7.6 for a full- length rupture (Leonard, 2014; Thingbaijam et al., 2017; Stirling et al., 2023). Further work will be required to better resolve the potential for full-length rupture of the Jindabyne Thrust and hence constrain the maximum credible earthquake, however it is likely greater than MW 7.0. The trench across the Hill Top Fault exposed a ~2.5 - 3 m thick pile of alluvial sediments, with Silurian granodiorite bedrock encountered towards the base of the trench. Near the western end of the trench a vertical fault plane was exposed in the bedrock, with a clear fault gouge, overlain by sediments that were folded across the fault (Figure 7). An apparent vertical offset of 20 cm was measured across the faulted bedrock surface and overlying sediments. Near the top of the fault, the apparent vertical offset reduced to 3 cm. This may indicate more than one event since deposition of the basal sediments, or simply vertical tapering of slip near the free surface (McCalpin, 2009). PreliminaryOSL ages indicated that basal sediments above bedrock were deposited at ~ 24 ka, with unfaulted overlying sediments deposited at ~20 ka, implying a most recent event around the time of the last glacial maximum. This overlaps with the timing of the penultimate event on the Jindabyne Thrust, however it is not possible to determine whether the two faults ruptured at the same time. Fig. 7: Part of the north wall of the Hill Top Fault trench a) uninterpreted; and b) interpreted geology around the fault. Red lines show near-vertical fault offsetting bedrock and overlying sediments (with bedding indicated by black lines).