Brittle-Ductile Deformation and Fault Slip Behavior of a Shallow Subduction Thrust, Hikurangi Margin, New Zealand
Abstract
Shallow subduction thrust faults may accommodate displacement by a mixture of steady aseismic creep, transient slow slip events, post-seismic afterslip, and propagation of co-seismic slip. Spatial and temporal transitions between varied fault slip styles are reported from geophysical observations, but the geological signatures are unknown and underlying controls are not well understood. Here, we report on direct observations from an active thrust fault in the frontal wedge of the northern Hikurangi Margin, New Zealand, based on core samples recovered on International Ocean Discovery Program Expedition 375. This thrust is a splay fault that appears to have accommodated at least several kilometers of displacement, and is located in a region of the margin that has experienced both shallow historical tsunami earthquakes and repeated large slow slip events.
The recovered cores intersect the top of the fault zone at 304 m below the sea floor. The fault zone comprises a main upper, 18 m thick brittle-ductile fault and a deeper, less intensely fractured and brecciated, 10 m thick fault strand. These two brittle-ductile faults are separated by 30 m of less intensely ductilely deformed footwall with more faults and fractures than the undeformed footwall below the fault zone. The fault zone includes both wide breccias and well preserved ductile flow fabrics within hemipelagic sediments. This variation in structure is consistent with the fault zone hosting a range of deformation styles, possibly reflecting co-located seismic and aseismic slip. Possible controls on slip style in this case include temporal variations in strain rate, transient changes in fluid pressure, and/or stress state.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T54C..06F
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8170 Subduction zone processes;
- TECTONOPHYSICSDE: 8185 Volcanic arcs;
- TECTONOPHYSICS