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

280 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E PATA Days 2024 K E Y W O R D S Alpine Fault, paleo-earthquake timings, paleo-slip, Marble Hill, New Zealand (1) Paleoseismology Team, GNS Science, PO Box 30-368, Lower Hutt, New Zealand. (2) School of Geography, Environment & Earth Sciences., Victoria University, PO Box 600, Wellington. (3) Formerly of Paleoseismology Team, GNS Science, PO Box 30-368, Lower Hutt, New Zealand (4) School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Parkville, VIC 3010, Australia (5) Dept. of Geography, University of Sheffield, Western Bank, Sheffield S10 2TN, England *Email: r.langridge@gns.cri.nz / jamie.howarth@vuw.ac.nz R. Langridge (1) J.D. Howarth (2) W. Ries (3) U. Cochran (3) M. Sagar (1) G. Coffey (1) M. Quigley (4) J. La Greca (4) E.J. Rhodes (5) PALEOSEISMIC EVENT DATES AND PALEO-SLIPS FOLLOWING RIVER AVULSION AT THE MARBLE HILL SITE, ALPINE FAULT, SOUTH ISLAND, NEW ZEALAND A B S T R A C T Marble Hill, near the Maruia River, is a well-known offset terrace site on the northern section of the Alpine Fault. Recent studies have included mapping using airborne LiDAR and chrono- stratigraphic investigation of pits and trenches. Offset risers and channels are used to characterise Late Holocene slip and slip rate. Several of these markers across a suite of degradation terraces are offset a similar amount and LiDAR indicates the river avulsed and rapidly degraded prior to these offsets occurring. Three new trenches have revealed up to four paleo-earthquake ruptures that occurred within the last ~1400 years. The exact timing of these events is poorly constrained in the trenches, but they correlate well with paleoearthquake proxies from nearby lacustrine turbidites and landslide deposits. An earthquake recurrence interval of 375- 417 yr is estimated for this period. These data highlight the power of combining on- and off-fault datasets to assess future earthquake potential along active faults. I N T R O D U C T I O N The reverse dextral Alpine Fault is the main plate boundary fault and forms the major seismic hazard in the South Island of Aotearoa New Zealand (Fig. 1; Berryman et al., 2012; Sutherland et al., 2007). Traditionally, the Alpine Fault has been divided into sections (southern, central, northern etc.) that are defined by differences in slip rate, strike, complexity and recurrence interval data coming from paleoearthquake studies (Norris & Cooper, 2001; Howarth et al., 2021). The northern section of the Alpine Fault (AF-NS)