Paleoseismicity of the western Humps fault on the Emu Plain, North Canterbury, New Zealand

ABSTRACT The 2016 MW 7.8 Kaikōura Earthquake nucleated on The Humps fault, which ruptured across the Emu Plain in North Canterbury. The paleoearthquake history of the fault was poorly constrained prior to the 2016 earthquake. To determine the timing and single-event displacements (SED) of earthquakes on the fault we use Optically Stimulated Luminescence (OSL) and radiocarbon dates of faulted stratigraphy and analysis of faulting (i.e. geometry and slip) at the McLean-1 trench site. At the trench the fault trace trends east–west and primarily accommodated right-lateral strike-slip in 2016 (2 ± 0.2 m strike slip and 0.35 ± 0.05 m vertical slip northside downthrow). The Humps fault is more seismically active than previously thought and accrued slip during at least six surface rupturing paleoearthquakes. The timing of these earthquakes was: 9.8–15.3 ka BP (Event 1), 8.6–11.5 ka BP (Event 2), 8.1–10.9 ka BP (Event 3), 6.0–8.6 ka BP (Event 4), 1840 AD to 4.5 ka (Event 5), and 2016 AD (Event 6). These earthquakes have a mean recurrence interval of 1.8–3.4 kyr and could have recurrence intervals up to ~9 kyr. Kaikōura-type ruptures could occur as frequently as every ∼2 kyr and maybe longer if The Humps fault rupture geometries are not characteristic.