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

extends from near Hokitika, where the fault encounters the SW corner of the Marlborough Fault System (MFS), to at least The Big Bend (a major complexity) and on to the Wairau Fault, which is the northernmost of the MFS faults. A significant body of paleoseismic data exists for the Alpine Fault summarised in Howarth et al. (2018). Gaps exist for on-fault paleoseismic records along the AFNS. Here there is evidence to suggest that the most recent faulting event (MRE) post-dates the well-known date of 1717 CE applied to the southern and central sections. Therefore, further paleoseismic trenching studies are required to test against other records from off-fault proxies. The Marble Hill site on the AF-NS was introduced to the PATA Days community at the 8th PATADays in 2017 (Fig. 2; Langridge et al., 2017; Upton et al., 2017). Marble Hill is important as it provides insights into fault slip per event, slip rate, and paleoseismicity at the transition from the AF- NS into The Big Bend area and Awatere Fault. In addition, there is an interplay between earthquake geology and landscape change in the Springs Junction area whereby proxies and river avulsion provide useful insights to paleoseismicity. In this paper we review the displacements and slip rate at the Marble Hill site and then summarise results from trenches across the fault. We relate these on-fault paleoearthquake timings to proxy timings from lacustrine turbidites and landslide deposits. Based on these data we can qualitatively assess the slip per event during the last 3-4 paleo-earthquake ruptures at this site. These results contribute to a wider understanding of paleo-slip and rupture length along the AF-NS. This is particularly relevant given the 75% probability of rupture on the central section in the next 50 years of M≥8 (Howarth et al., 2021). Fig. 1: South Island tectonic setting. The central (bold black) and northern (yellow) sections of the Alpine Fault are highlighted. On-fault and off-fault (lakes; circles) paleoseismic sites are indicated. BB, Big Bend.