An isoseismal map shows the Modified Mercalli Intensities (MMI) reported from a particular earthquake. To use the metaphor of a lightbulb; an earthquake has a fixed magnitude (the Watt rating of the bulb), but the intensity varies with distance (the brightness of the light). By plotting intensities we can learn more about the direction and distance energy waves travel through the crust, which can help us determine the types of fault on which the earthquake occurred.
Isoseismal maps are derived from felt reports – accounts from people who felt the earthquake. We also ask people to fill in these reports when they are in the earthquake area and did not feel it, as this may reveal something about the local geology.
The image shows earthquakes that have occurred in southeastern Australia (up to 2012) for which the SRC has generated isoseismal maps. Click on the place name in the list below to download the PDF isoseismal map report.
Tamworth, 2012, magnitude 4.4
Appin, 1999, magnitude 4.5
Swan Hill, 2001, magnitude 4.8
Echuca, 2008, magnitude 3.4
Caulfield, 2006, magnitude 2.5
Tooradin, 2001, magnitude 3.7
Korumburra, 2009, magnitude 4.7
Moe, 2012, magnitude 5.5
Mt Baw Baw, 1996, magnitude 5.0
Lake Sorell, 2002, magnitude 4.4
Woods Point, 2021, magnitude 5.8
We’ve generated a contoured isoseismal map from over 40,000 reports submitted to Geoscience Australia for the magnitude MLv5.8 (Mw5.9) Woods Point earthquake that occurred at 9:15am AEST on 22 September 2021. This was the largest earthquake to occur in Victoria since record-keeping began.