Accommodating ~9 m of dextral slip on the Kekerengu Fault through ground deformation during the Mw 7.8 Kaikōura Earthquake, November 2016

The Mw 7.8 Kaikōura earthquake of November 14th 2016 provided unprecedented opportunities to understand how the ground deforms during large magnitude strike-slip earthquakes. The re-excavation and extension of both halves of a displaced paleoseismic trench following this earthquake provided an opportunity to test, refine, and extend back in time the known late Holocene chronology of surface rupturing earthquakes on the Kekerengu Fault. As part of this thesis, 28 organic-bearing samples were collected from a suite of new paleoseismic trenches. Six of these samples were added to the preferred age model from Little et al. (2018); this updated age model is now based on 16 total samples. Including the 2016 earthquake, six surface rupturing earthquakes since ~2000 cal. B.P. are now identified and dated on the Kekerengu Fault. Based on the latest five events (E0 to E4), this analysis yields an updated mean recurrence interval estimate for the Kekerengu Fault of 375 ± 32 yrs (1σ) since ~1650 cal. B.P. The older, sixth event (E5) is not included in the preferred model, as it may not have directly preceded E4; however, if this additional event is incorporated into an alternative age model that embraces all six identified events, the mean recurrence interval estimate (considered a maximum) calculated is 433 ± 22 yrs (1σ) since ~2000 cal. B.P.   Comparison of structures on an identical trench wall logged both before and after the 2016 earthquake, and analysis of pre- and post-earthquake high resolution imagery and Digital Surface Models (DSMs), has allowed the quantification of where and how ~9 m of dextral-oblique slip was accommodated at this site during the earthquake. In addition to this, I analyse the coseismic structure of the adjoining segment of the 2016 ground rupture using detailed post-earthquake aerial orthophotography, to further investigate how geological surface structures (bulged-up moletrack structures) accommodated slip in the rupture zone. These combined analyses allowed me to identify two primary deformation mechanisms that accommodated the large coseismic slip of this earthquake, and the incremental effect of that slip on the structural geology of the rupture zone. These processes include: a) discrete slip along strike-slip faults that bound a narrow, highly deformed inner rupture zone; and b), distributed deformation within this inner rupture zone. The latter includes coseismic clockwise rotation of cohesive rafts of turf, soil and near-surface clay-rich sediment. During this process, these “turf rafts” detach from the underlying soil at a mean depth of ~0.7 m, shorten by ~2.5 m (in addition to shortening introduced by any local contractional heave), bulge upwards by