A Kinematic Model of the Northeast Australian Plate Boundary Zone

Zhao Siyuan1, McClusky Simon1, Koulali Achraf2, Cummins Phil1, Miller Meghan1

1The Australian National University, Canberra, Australia; 2 Newcastle University, Newcastle upon Tyne, United Kingdom

The northeast Australian plate boundary zone encompasses a complex tectonic environment, characterised by the rapid convergence of the Pacific, Australian, Philippine Sea plates and the Sunda Block. The mechanism driving the oblique convergence in this region and the activity and partitioning of fault slip rate within this deformation zone have hitherto been conjectural. In this study, we perform a simultaneous inversion of 500 earthquake slip vectors and 236 GPS velocities to quantify the kinematics of block bounded faults within the deformation zone spanning the Sunda-Banda Arc, Irian Jaya region and Papua New Guinea. Our best fitting kinematic block model comprises 23 elastic blocks, for which we estimate the rotation rates, uniform horizontal strain rate tensor, and block boundary slip rates. The compressional component of the convergence between the Sunda Block and Australian Plate is largely accommodated by the Sunda-Banda forearc and back-arc, and ~34 % of the shear component is transferred to the eastern back-arc through the Semau Fault. The Bird’s Head block is rotating 2.642 ± 0.070 °/Myr anticlockwise with respect to the Australian plate, resulting in average 44.3 mm/yr motion across the Seram Trough and the formation of the Cendrawasilh Bay sphenochasm. The relative slip vectors across the New Guinea Fold-and-Thrust Belt indicate a transition in the regime of the block boundary from predominately thrust faulting at its western segment with an average convergence rate ~13.6 mm/yr, to the predominately left-lateral strike-slip in the middle segment with a slip rate of 7-8 mm/yr, then again to thrust in the eastern segment of New Guinea Highlands with an average convergence rate up to 10.0 ± 0.5 mm/yr. In the western part of the New Guinea Highlands, the fault-parallel slip rate decreases from 27.8 ± 0.7 mm/yr to 19.8 ± 0.6 mm/yr, and the average fault-parallel slip rates in the western New Guinea Highlands is greater than that of in the eastern segment (23.3 mm/yr and 5.5 mm/yr respectively), which implies some of the subsidiary movement of the highly active sinistral Tarera-Adiuna Fault may be accommodated within the Highlands thrust belt. The available GPS measurements of crustal motion suggest interseismic strain accumulation associated with normal faulting along the Banda detachment, and the low subsidence rates observed in the outer arc are consistent with weaker strain accumulation in the fold-and-thrust belt. In our model, the New Guinea Highlands thrust belt accommodates less than 13% of convergent and 17% of left lateral motion between the Australian and Pacific plates, and the rest of the convergence is largely accommodated by the New Guinea Trench with a slip rate up 84.2 ± 2.5 mm/yr. Our best-fit model also reveals 2.195 ± 0.117 °/Myr anticlockwise rotation of the Woodlark crustal block relative to the Australian Plate, which produces a seafloor spreading rate of 28.9 mm/yr in the Woodlark Basin and 15.9 mm/yr of extension in the continental rift in the Papuan Peninsula. Multiple normal structures located in the D’Entrecasteaux Islands accommodate the extensional deformation, slipping at high rates around 17.7 mm/yr.


Biography:

I did my Honours degree in the University of Adelaide, and finished my Masters degree in the Australian National University (ANU). Now, I am a PhD candidate in ANU. My research interest is using geodetic measurements (like GPS and InSAR) to investigate the active deformation of the Earth’s crust.

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