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Abstract : The 1000 km-long Hikurangi subduction margin, where the Pacific plate subducts beneath the North Island of New Zealand, is the country’s largest earthquake and tsunami hazard. The seismic behaviour of the subduction interface includes interseismic coupling on the subduction thrust and the occurrence of slowslip events. The potential hazard, however is largely unknown because of the short (< 170 years) historical record of seismicity relative to the likely recurrence of great earthquakes. Marine turbidite paleoseismology provides a means to build long-term event records. We first used a series of deep sediment cores collected along the 200 km-long northern section of the Hikurangi Margin. Stacks of cm-thick turbidites, interbedded with hemipelagite and tephra beds, provide great potential for age control through radiocarbon dating and chronostratigraphy. Core correlations across the northern margin using similarities in sedimentary facies, lithostratigraphy, physical properties and ages indicate the synchronicity of 19 turbidites since 7500 yr BP. Analyses indicate that 17 are the distal expression of synchronous earthquake-triggered submarine landslides that occurred on the continental slope. This paleoearthquake record includes events from the upper plate and the plate interface. Empirical relations that combine Peak Ground Acceleration and earthquake characteristics helped us to deduce the earthquake’s source and magnitude. Compared to the present active fault catalogue, this approach identifies 17 synchronous turbidites deposited from 390±170 to 7480±120 yr BP which recorded the rupture of three active faults, including the subduction interface, all triggered by earthquakes ≥ Mw 7.3. The temporal distribution of events suggests an erratic tectonic regime of the subduction interface with periods of high earthquake frequencies and periods of low earthquakes frequencies. In November 2016, an RV Tangaroa voyage acquired 50 sediment cores (< ~5.5 m) along the southern half of the Hikurangi Margin. Sites were selected using multibeam bathymetric and backscatter data, subbottom profiles, archived sediment samples, and results from numerical modelling of turbidity currents. Sites fell into three categories: turbidite distributary systems; small isolated slope-basins; and Hikurangi Channel, levees and basin floor. Typical of the margin, the terrigenous-dominated sequence included layers of gravel, sand, mud and volcanic ash. Some cores contain up to 25 individual turbidites, potentially earthquaketriggered. This library of turbidites provides the basis of extending the paleoseismic records to the entire Hikurangi Margin. Strong ground shaking beneath the NE South Island associated with the 14th November 2016 (NZDT) Mw 7.8 Kaikoura Earthquake occurred during the voyage. Within five days of the earthquake, we recovered with a multicorer what appeared to be a very recently emplaced co-seismic turbidite about 10-20 cm thick over a region extending c. 300 km from the Kaikoura coast. This offers a rare opportunity to calibrate paleoseismic data and to test hypotheses of turbidite triggering and emplacement. Analysis of the five cores that detected this highly fluidised layer overlying the pre-earthquake seabed clearly visible as an oxidised layer is ongoing. Integrating earthquake records along the entire margin will be critical to single out events sourced from the plate interface from the large number of those from the upper plate.
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Submitted on : Tuesday, February 27, 2018 - 9:19:39 AM
Last modification on : Tuesday, October 19, 2021 - 9:07:58 PM


  • HAL Id : insu-01718036, version 1



Geoffroy Lamarche, Alan Orpin, Philip Barnes, Jamie Howarth, Hugo Pouderoux, et al.. SEARCHING FOR GREAT EARTHQUAKE RECORDS FROM RUPTURE OF THE HIKURANGI SUBDUCTION PLATE INTERFACE USING TURBIDITE PALEOSEISMOLOGY. International Meeting of Sedimentology 2017, Oct 2017, Toulouse, France. pp.482. ⟨insu-01718036⟩



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