Thursday 4 December 2014

Magnitude 3.3 Earthquake in Victoria State, Australia.

The United States Geological Society reported a Magnitude 3.3 Earthquake at a depth of 10 km in the Shire of Cardinia in Victoria State, Australia, at about 6.05 am local time on Thursday 4 December 2014 (about 7.05 pm on Wednesday 3 December GMT). A quake of this size is highly unlikely to have caused any damage or injuries, but is large for the area, and people reported feeling it as far away as Melbourne, about 50 km to the northwest.

The approximate location of the 4 December 2014 Shire of Cardinia Earthquake. Google Maps.

Victoria is located far from any active tectonic boundary and is not an obvious place to expect earthquakes. The convergent boundary between the Pacific and Australian Plates is at its closest in South Island, New Zealand. The boundary with the Antarctic Plate far to the south is a divergent margin, which is slowly pushing Australia to the north, which accounts for some tectonic stress in the region.

More relevantly, the geology of the east of Victoria is dominated by ancient fold mountains, formed by pressure on the rocks during the assembly of the ancient supercontinent of Pangea during the Palaeozoic. This caused the flat layers of rock in the Earth's crust too fold up to form mountains, in much the same way as a piece of paper pushed from both ends. These mountains have largely eroded away today, but the layers of rock beneath eastern Victoria are still folded, stacked up against one-another rather than laid flat on top of one-another. This is a less stable arrangement, so tectonic pressures can lead to larger quakes here than might otherwise be expected.
See also...

http://sciencythoughts.blogspot.co.uk/2014/11/melbourne-woman-swallowd-by-3-m-sinkhole.html
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