According to catastrophe modeling firm AIR Worldwide, at 10:53 UTC this morning, the biggest earthquake to hit Victoria, Australia, in more than a century struck. The U.S. Geological Survey (USGS) issued a moment magnitude of 5.2 for the event and Geoscience Australia issued a moment magnitude of 5.3. Today’s earthquake struck near the southeast coast of Australia 10 km southwest of Moe, the closest population centre, and 120 km southwest of Melbourne, Australia’s second-largest metropolis with a population of more than 4.1 million. AIR does not expect significant insured losses from this event.
According to the USGS, the earthquake struck at a depth of 9.9 km, making this a shallow event. Shaking lasted for 30 to 40 seconds, according to local accounts.
“Australia is in a stable continental region, thus damaging earthquakes there are relatively rare,” said Dr. Bingming Shen-Tu, senior principal scientist at AIR Worldwide. “When they do occur, however, ground motion is typically felt over a large area. Although Australia exhibits comparatively low seismic activity, earthquakes have been recorded in almost all regions of the country. Seismicity in eastern Australia, where today’s earthquake occurred, is relatively low as compared to western and northwestern Australia.”
“However, for eastern Australia, the historic earthquake activity in the area that includes the southeastern coastal and offshore regions from Melbourne to Tasmania Sea is relatively high. This event occurred in a failed continental rift zone in southern Australia. A series of neotectonic faults have been mapped along the southwestern coastal areas and the northern margin of the failed rift. A couple of magnitude 5 – 5.3 earthquakes occurred in 1969 about 25km east of the epicenter. Most of the historical events in this region are relatively small in magnitude. However larger events of magnitude 6.5 to 7 have occurred in the eastern offshore area off Tasmania, about 250 to 300 km southeast of this event.”
According to AIR, building vulnerability varies across Australia, with regional disparities due to differences in building code implementation and enforcement, and construction practices and materials. Australia’s commercial building stock is dominated by masonry construction, while residential construction is a mix of wood frame and masonry. Australia has a number of residential construction types that are unique to the country, including cavity double-brick masonry, which is extremely vulnerable to ground shaking.
In Melbourne, residents reported windows rattling and floors rocking. Reports of minor damage include cracks in the walls of buildings and shelves falling over.