11:30 〜 11:45
[SCG52-10] Geometry, tectonics and earthquakes at the southern termination of the Hikurangi subduction margin
★Invited Papers
キーワード：Subduction interface, upper plate faults, great earthquakes
The active Hikurangi subduction margin extends for over 1000 kms and terminates east of central New Zealand. The southern Hikurangi subduction interface hosts great earthquakes (Mw>8) about every 500 years and is inferred to have ruptured historically. At the termination of the southern Hikurangi margin oblique subduction transitions across the Marlborough Fault System (MFS) to transpression on the Alpine fault. This transition is distributed across many faults in the upper plate, while the southern extent of active subduction is a topic of debate. While some studies suggest that subduction ceases northeast of the MFS, seismicity and InSAR data indicate an active interface beneath the northern South Island. GPS, focal mechanisms and coastal uplift during the 2016 Kaikōura earthquake are consistent with slip on the interface (and/or related thrusts), which diminishes southwards. Earthquake hypocentres define a Benioff zone with subduction extending at least 80 km south of the seafloor expression of the subduction thrust. Paleoearthquake studies indicate co-rupture and/or sequences of earthquakes closely spaced in time on subduction interface and upper-plate faults. Earthquake clustering is consistent with geometric intersection and/or stress interactions between upper-plate faults and the subduction interface.