As Australia does not sit anywhere near a fault line, how did it experience an earthquake today?
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It doesn’t sit anywhere near a tectonic boundary. It does have a number of fault lines.
Tectonic plates undergo a lot of stress. They can fracture quite far from their boundaries. These are fault lines. Through them stress can be released.
Tectonic plates also over time fracture into multiple new plates (they also fuse together).
I really liked the explanation given by Trevor Allen who is a seismologist with Geoscience Australia;
Imagine if you will, that a tectonic plate is analogous to a pavlova — with a thin brittle crust lying above a ductile, but mostly solid meringue mantle, the Australian continent would sit in the middle of our pavlova.
If you put your hands on the edge of the pavlova and start to squeeze, the crust around your hands will be the first to break, like those earthquakes at the boundaries of tectonic plates. But if you continue to squeeze, eventually strain builds up in the centre of the crust, and cracks will begin to appear.
This is similar to how we get earthquakes in Australia. The same forces that drive earthquakes on tectonic plate boundaries are at play — they just take a lot longer to manifest in the middle of our pavlova
You can have fault lines very far from the tectonic boundaries. These are caused by internal stresses in the tectonic plate. Quite often these stresses build up at the center of the plate as the different sides of the plate is moved in different directions by the surrounding plates and the current of magma under them. Most famous such fault in the volcanos of Hawaii which take place in the middle of the Pacific plate as far from any tectonic plate boundry as you get. But most tectonic plates do have internal fault lines.
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