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Submarine paleoseismology of the northern Hikurangi subduction margin of New Zealand as deduced from Turbidite record since 16 ka

Abstract : Paleoseismic studies seek to characterise the signature of pre-historical earthquakes by deriving quantitative information from the geological record such as the source, magnitude and recurrence of moderate to large earthquakes. In this study, we provide a w16,000 yr-long paleo-earthquake record of the 200 km-long northern Hikurangi Margin, New Zealand, using cm-thick deep-sea turbidites identified in sediment cores. Cores were collected in strategic locations across the margin within three distinct morphological re-entrants e the Poverty, Ruatoria and Matakaoa re-entrants. The turbidite facies vary from muddy to sandy with evidence for rare hyperpycnites interbedded with hemipelagites and tephra. We use the Oxal probabilistic software to model the age of each turbidite, using the sedimentation rate of hemipelagite deduced from well-dated tephra layers and radiocarbon ages measurements on planktonic foraminifera. Turbidites are correlated from one core to the other using similarity in sedimentary facies, petrophysical properties and ages. Results show that 46 turbidites are synchronous along the entire margin. Amongst them 41 are interpreted as originating from the upper continental slope in response to earthquake-triggered slope failures between 390 170 to 16,450 310 yr BP. Using well-established empirical relationships that combine peak ground acceleration, magnitude and location of earthquakes, we calculate that synchronous slope failures were triggered by the rupture of 3 of the 26 known active faults in the region, each capable of generating Mw 7.3 to 8.4 earthquakes e two are crustal reverse faults and one is the subduction interface. The 41 Mw 7.3 earthquakes occurred at an average recurrence interval of w400 yr over the last w16,000 yr. Among them, twenty are interpreted as subduction interface earthquakes that occurred at an average recurrence interval of w800 yr, with alternating periods of high activity and low return times (305e610 yr) and quiescence periods with high return times (1480e2650 yr). Based on turbidite paleoseismology, we propose that subduction interface earthquakes were of lower magnitude during active periods (Mw > 7.5) than during quiescence periods (Mw 8.2).
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Hugo Pouderoux, Jean-Noël Proust, Geoffroy Lamarche. Submarine paleoseismology of the northern Hikurangi subduction margin of New Zealand as deduced from Turbidite record since 16 ka. Quaternary Science Reviews, Elsevier, 2014, 84, pp.116-131. ⟨10.1016/j.quascirev.2013.11.015⟩. ⟨insu-00934455⟩

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