3D seismic investigation of sedimentation and deformation in the Tuaheni Basin, Hikurangi Margin, New Zealand
Abstract
Forearc and trench slope basins provide crucial information on tectonic deformation and sedimentation processes at subduction margins. Along the northern Hikurangi margin, frequent and unusually shallow slow slip events along the megathrust fault have inspired many recent geological and geophysical studies. We investigate the evolution of the accretionary prism, using newly acquired 3D seismic reflection and refraction data offshore Poverty Bay. We focus on the ~14 km wide Tuaheni basin. It is the location of IODP drill site U1519 and lies above the slow-slip earthquake source region. During the acquisition on R/V Marcus Langseth, we deployed four 6-km streamers, and fired two 3300in3 18-gun source arrays over a total area of 14.7km x 60km. Additionally, we deployed 100 ocean bottom seismometers and used first arrival tomography to produce a 3D P-wave velocity model that enabled us to convert the 3D post-stack migrated data to depth. We examined the 3D geometry of three slope basin units, previously identified at drill site U1519. The deepest, Seismic Unit 3 forms the basement of the basin and consists of landward dipping reflector packages in the hanging walls of thrust faults that produce variations in basement topography. Some thrusts have remained active during deposition, causing uplift and folding of the seaward-most basin strata. The seaward edge of the basin is formed by uplift of strata along one of the thrust faults. Unit 2 is a seaward-dipping sedimentary sequence up to 1km thick at the basin edge that onlaps Unit 3 in the NW and underlies the North Tuaheni slope. The youngest unit, Unit 1, is a flat-lying sequence up to 600m thick comprising recent turbidites and mass transport deposits that sequentially onlaps the North Tuaheni slope to the northwest. Along-strike variations in the basin are caused by differential movement of thrust fault blocks of Unit 3. The offset in these fault blocks is mostly covered by the thick, basin fill sediment of Units 1 and 2. However, west of the basin, a thrust ridge, the Tuaheni Bank, cuts the basin and separates it into two 2-5 km-wide sub-basins. This study provides the first look at the Tuaheni basin in 3D and provides insight into the past deformation above the Hikurangi megathrust.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T42C..01T
- Keywords:
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- 8045 Role of fluids;
- STRUCTURAL GEOLOGY;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS;
- 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS