Isoseismal Maps

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 may learn more about the mechanisms for earthquakes in those areas.

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.

Below are some isoseismal maps from earthquakes in our area of operation.

	2009 Mar 06	Korumburra, VIC (pdf)			2001 Oct 27	Swan Hill, VIC (jpg)
	2008 Mar 01	Echuca, VIC (pdf)			2001 Aug 22	Tooradin, VIC (pdf)
	2006 Oct 22	Caulfield, VIC (pdf)			1999 Mar 17	Appin, NSW (pdf)
	2002 Jun 15	Lake Sorell, TAS (pdf)			1996 Sep 25	Mt Baw Baw, VIC (jpg)

Although seismographs have been operated in Australia for over 100 years, until about 1960 these were optimised to record large distant earthquakes. They were too insensitive, and there were too few of them to record most local earthquakes. The locations and magnitudes of most Australian earthquakes before 1960 were estimated using earthquake intensity reports. Many of these have been summarised in one of three earthquake atlases published by the Australian Geological Survey Organisation.

Atlas of Isoseismal Maps of Australian Earthquakes

Part 1, 1982, BMR Bulletin 214, compiled by I.B. Everingham, A.J. McEwin and D. Denham.

Part 2, 1987, BMR Bulletin 222, compiled by J.M.W. Rynn, D. Denham, S, Greenhalgh, T. Jones, P.J. Gregson, K.F. McCue and R.S. Smith.

Part 3, 1996, AGSO Record 1995/44, compiled by Kevin McCue.

On this web site, references to these are listed as Atlas 1, Atlas 2, and Atlas 3 respectively. Other publications on specific earthquakes are referenced individually.