University of Cambridge > > Bullard Laboratories Wednesday Seminars > Validating the turbidite approach to paleoseismology using observations from the Mw7.8 Kaikōura earthquake, New Zealand

Validating the turbidite approach to paleoseismology using observations from the Mw7.8 Kaikōura earthquake, New Zealand

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Turbidite paleoseismology is based on the along‐strike correlation of deep-water turbidite deposits, formed in response to earthquake-triggered strong ground motions. The approach has produced some of the longest and most complete records of Mw7 to Mw9 earthquakes on subduction zones. However, the veracity of the technique is still vigorously debated due to uncertainty in the relationships between fault source, the spatial distribution of ground motions and turbidite emplacement for a given earthquake. The debate can only be resolved by direct observations of these relationships that remain extremely rare. The 2016 Mw 7.8 Kaikōura earthquake in New Zealand provides a unique opportunity to test the turbidite approach to paleoseismology because the fault source is relatively well defined, ground motion models are well calibrated and post-event sediment cores constrain the spatial distribution of turbidite emplacement. Turbidites revealed in sediment cores from along the Hikurangi margin demonstrate near ubiquitous triggering of turbidity currents in 11 discrete canyon systems along the slope margin up to 110 km north of the rupture tip. The spatial distribution of turbidite emplacement agrees well with ground motions predicted by physic-based simulations and shows that the threshold required to emplace turbidites is a PGV ≥ 18 cm/s. Moreover, grainsize pulsing at the base of turbidites correlates well with PGV amplitude peaks above the triggering threshold providing confirmation of the contentious hypothesis that turbidite pulsing records information on earthquake seismograms. Ultimately, the relationships between turbidite emplacement, ground motions and fault source observed during the Kaikōura earthquake support the use of earthquake-triggered turbidites as a reliable paleoseismic proxy.

This talk is part of the Bullard Laboratories Wednesday Seminars series.

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