Constraining the deformation history of the frontal wedge of Hikurangi Subduction Margin with analog modeling and bedding trends from borehole logging of IODP Expedition 372
Abstract
IODP Expeditions 372/375 were conducted at the Hikurangi Subduction Margin (HSM) off the eastern North Island, New Zealand, to investigate slow slip earthquakes (SSEs). At site U1518 a thrust fault in the frontal wedge was drilled in the region of at the deformation front of the subduction margin. This area of the frontal wedge includes the shallowest part of the plate boundary and experiences shallow SSEs. In addition, fault rupture propagation in the region has tsunamigenic potential to generate events such as the 2011 earthquake in Japan. Thus, it is important to consider the kinematics of how this frontal wedge was formed and subsequently deforms.
Analysis of bedding orientations defined using logging-while-drilling (LWD) resistivity imaging during Exp.372 shows that the hanging wall sediments at site U1518 have NE dip directions, except for the interval 170.5-229.5 mbsf where bedding dips SW and a number of conductive and resistive fractures are observed. In addition, the bedding trends of Exp. 375 core-result agrees well with the trends from the of Exp. 372 LWD resistivity images. We hypothesize that the thrust fault and associated folding in the hanging wall are related to seamount subduction and employ analog model experiments with the Digital Image Correlation (DIC) to test. DIC is the technique to visualize the fault activity in analog modeling. The experimental setup consists of a box of 25 x 90 x 30 cm with a moving wall, side-glass panes, and a Teflon-surfaced basement. The seamount model was set 55 cm from the model walls. For experiments, the initial sand thickness was 2 cm and color layers are installed inside to visualize and trace the development of bedding orientations and internal structure. Preliminary results show a rapidly growing the surface slope with the subduction of the seamount, followed by slope failure activating in the most frontal portion. The slope growth became active after the seamount passes through the front. The slope failure resulted in a mass transport deposit onto the footwall and consequently subducted. The position of this subducted deposits was just below the fore thrust with thick transported deposition. In addition, the development of a piggyback basin was observed. The change of bedding dip within the piggyback basin shows the similar trends to the bedding estimated using LWD data.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T51I0302K
- 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