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

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 - two are crustal reverse faults and one is the subduction interface. The 41 Mw ≥ 7.3 earthquakes occurred at an average recurrence interval of ∼400 yr over the last ∼16,000 yr. Among them, twenty are interpreted as subduction interface earthquakes that occurred at an average recurrence interval of ∼800 yr, with alternating periods of high activity and low return times (305-610 yr) and quiescence periods with high return times (1480-2650 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).