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Here are some maps I've produced of the aftershock data from Sunday's great earthquake. Seismologists call all earthquakes over Magnitude 8.0 "great". As it happens this is the fourth largest ever recorded with an energy release approaching the limit of what is possible from a conventional earthquake.

The first map shows a zoomed in area around the main fault slip and aftershocks. Scientists will already be trying to determing which area of the megathrust fault slipped, and how far it slipped. The biggest piece of evidence is actually this map. The aftershocks usually map out the fault segment that slipped. As you can see from this map, a huge area of the fault slipped. The fault was dipping at a shallow angle (deepest in the north east), so the slipped zone is spread over a wide area.

The USGS are currently quoting an area of 1200km x 100km slipping with average displacement of 15 metres.

For comparison, in the 1906 San Francisco earthquake, approximately 260 miles of vertical fault slipped to a depth of about 10 miles-ish.



The following map is a regional map. Note that the scale for the earthquakes has changed so that they do not obliterate the map.
Japan also sits on a subduction zone, and has received some earthquakes iin the past 7 days - this is usual. There's also a small earthquake near Cyprus. Occasional medium sized earthquakes are usual for the East Mediterranean.



The data for the above maps came from the USGS at:

http://wwwneic.cr.usgs.gov/neis/bulletin/

This feed is regularly updated with the latest earthquakes worldwide, and lists them for seven days. (the above maps were taken with data from 9:30PM CST).

The USGS also have a preliminary report here:

http://neic.usgs.gov/neis/bulletin/neic_slav_ts.html


Richard Marsden

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