title: Pre-historic ruptures on 2016 Kaikōura earthquake faults and implications for seismic hazard
Creators: name: Langridge, Robert L.
name: Nicol, Andy
name: Barrell, David J A
name: Almond, P
name: Clark, Kate J
name: Stirling, Mark W
Publisher: name: GNS Science
Year: 2019

description:  The 14 November 2016 Mw 7.8 Kaikōura Earthquake was one of the largest and most complex on-land earthquakes ever observed globally and ruptured at least 14 faults with displacements of >1.5 m. The earthquake ruptured faults progressively from near the epicentre in the southwest on The Humps Fault in the North Canterbury (NCD) domain, northeast into the Marlborough Fault System (MFS) and on to Cape Campbell, including rupture of submarine faults and extensive uplift of the Marlborough coast.
NHRP- and EQC-funded research into the paleoseismicity of NCD faults has indicated that in general these faults, e.g. The Humps, Leader, Stone Jug, Conway-Charwell and Hundalee faults, each have had multiple Holocene earthquake ruptures with an average recurrence interval of 2500–4000 years (where long enough records exist). Slip rates of 0.5 mm/yr have been estimated for The Humps Fault.
This work has significantly advanced our understanding of the activity of faults in the NCD region. Results indicate that these faults may operate together in multi-fault earthquake ruptures, or rupture in a sequence over relatively short time periods (years to centuries) in a cluster of seismic release. The results also highlight that the NCD region that includes these faults was under-represented in the national seismic hazard model (NSHM-2012).
Paleoseismic studies undertaken on the Papatea Fault indicate that it is an important active plate boundary fault that has had at least three earthquake ruptures during the past 1000 years. The main and western strands of the Papatea Fault can rupture at the same time (and sometimes with the Corner Hill Fault as seen in 2016), and the timing of Papatea Fault earthquakes is also similar to the last few paleo-earthquakes on the Kekerengu Fault. The average recurrence interval of earthquakes on faults in the south-eastern part of the MFS, including the Hope, Jordan, Kekerengu and Papatea faults is 300–500 years, which is consistent with the high slip rates of these faults. Our results offer the possibility that this group of faults can rupture all together, as they did in 2016, or as a sequence of events spaced closely in time. Ongoing studies of the Hope Fault, and landscape impacts in the Clarence River valley may help elucidate when multi-fault or multi-segment ruptures versus single-segment/fault earthquakes have occurred in the past.
In summary, the recurrence interval of MFS and NCD faults is an order of magnitude different. Earthquakes occur on the main MFS faults approximately 10 times more often than they occur on the NCD faults. Multi-fault earthquakes have probably occurred in the past in both the NCD and MFS regions (individually). However, the occurrence of fault ruptures across both domains in the 2016 Kaikōura earthquake was a highly unusual event. Multi-fault ruptures spanning the NCD-MFS domains are being incorporated into the next generation of seismic hazard models, along with the other important outcomes of this research.
Preliminary results from this project have been communicated to stakeholders including NCTIR, the district councils and the public through several presentations. (auth)