Here's a good explanation on Australia's rocks, nothing formal but simple:
"You are right. Australia is not near a tectonic plate boundary and so it does not suffer earthquakes directly from that source. Australia is an "old" continent made up of deep layers of old rocks which date back to Precambrian times. These old rocks form thick slabs of rock called cratons - eg the Yilgarn craton in Western Australia. These huge areas of cratons act like thick, massive slabs of rock which are less prone to deformation and failure under crustal stresses. The Earth's crust is much thicker in such areas.
In many areas of Australia upwelling granite magma over time has solidified to "weld" the thick granitic crust togetrher thus further reinforcing it."
"You are right. Australia is not near a tectonic plate boundary and so it does not suffer earthquakes directly from that source. Australia is an "old" continent made up of deep layers of old rocks which date back to Precambrian times. These old rocks form thick slabs of rock called cratons - eg the Yilgarn craton in Western Australia. These huge areas of cratons act like thick, massive slabs of rock which are less prone to deformation and failure under crustal stresses. The Earth's crust is much thicker in such areas.
In many areas of Australia upwelling granite magma over time has solidified to "weld" the thick granitic crust togetrher thus further reinforcing it."
My religion is the understanding of my world. My god is the energy that underlies it all. My worship is my constant endeavor to unravel the mysteries of my religion. 
