Seminar Series

Title: Controls on Earthquake Induced Landslides and Lessons from the 2016 Mw 7.8 Kaikōura Earthquake


Colin Bloom - PhD student in palaeoseismology.


Time & Place

Thu, 28 Apr 2022 16:00:00 NZST in ER263 and Zoom


Abstract: Globally, significant effort has gone into developing better regional landslide forecasts using machine learning modeling, but there remains a surprising amount of uncertainty regarding the predictive parameters used to train these models and the physical processes that these parameters represent. The 2016 Mw 7.8 Kaikōura earthquake on the northeast South Island of New Zealand triggered more than 30,000 landslides in one of the most complex rupture sequences ever recorded. Here, I provide an overview of regional controls on coseismic landslides from the 2016 Kaikōura earthquake and examine two factors in detail: (i) the attenuation of landslide density with distance from surface fault ruptures and (ii) concentrations of coastal cliff failure in areas with low modeled ground motion that, while rarely considered in modeling, still represent a relevant coseismic hazard. Three-dimensional surface displacements from photogrammetric point clouds are used to constrain the width of off-fault deformation (OFD) around fault ruptures. Landslide density is generally higher within OFD zones and the attenuation of landslides with distance from the fault does not mirror the attenuation of regionally-modeled peak ground accelerations. This suggests that slope stability is, in part, controlled by decreased rock mass strength and/or amplification of strong ground motions near surface rupturing faults. Eight historical image sets are used to constrain the last 72 years of coastal cliff collapse at Conway Flat, an 8 km section of coastal cliffs south of Kaikōura exposed to wave-action at high tide. Over the historic record at Conway Flat, infrequent strong ground motion including the 2016 Kaikōura earthquake, appears to dominate the rate of cliff retreat. Debris, that would otherwise serve as evidence of widespread failure, is quickly evacuated within one to two decades of the event. The cliffs at Conway Flat are similar to other coastlines around the globe. Given a relatively low ground motion threshold for cliff collapse at Conway Flat, the influence and risk of earthquakes may be underestimated under similar conditions elsewhere.



Zoom link