ABSTRACT:

Tectonic processes along the northern boundary of the Australian plate affect the distribution and occurrence of geological hazards on the North West Shelf. The North West Shelf extends across a transition from an active collisional plate boundary in the north to a passive "Atlantic-type" continental margin along the west coast. The active collisional processes in the north have formed significant seismic sources along the collisional plate boundary zone and moreover have reactivated former rift related structures along the passive margin. These reactivated structures also are potential sources of future large magnitude earthquakes, and are potential mechanisms for warping and tilting of the seafloor, and eventual mass wasting. The broad scale regional northward tilting along the North West Shelf has resulted in the subsidence of former coastal depositional environments below the recorded late Quaternary sea-level minima.

INTRODUCTION

Australia is commonly viewed as a stable continental regional with little tectonic activity and few geological hazards. Although it is a relatively stable continent (Johnston et al., 1994), the northwestern part of the continent is characterized by two types of plate boundaries: a relict passive Atlantic-type margin on the west and an active collisional plate boundary on the north (Bird et al., 2002). This paper provides preliminary data and observations which demonstrate that the stresses imposed on the plate due to the collision in the north are causing regional lithospheric scale warping, surface faulting, and reactivation of former rift-related structures along the North West Shelf. We also show that significant geohazards, such as submarine slope failures, are occurring along the relict passive margin as rejuvenated features associated with reactivation and inversion of former rifted margin structures. The tectonic subsidence of these coastal depositional environments affects the nature of soils in the foundation zones typical for offshore infrastructure developments.

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