Analysing maps of seismic activity to determine plate
motion
Step 1
Much information can be obtained about plate motion by examining the patterns of depth of
earthquakes at and adjacent to subduction zones. Go to
http://earthquake.usgs.gov/regional/world/seismicity/
Take a careful look at the pattern of earthquakes on the world seismic map.
Focussing question
Is there a trend in depth of earthquakes across subduction zones in terms of depth of
earthquakes? If so describe it.
Hint: To assist you to see the trend it may be beneficial to use the magnifier built into Accessories.
To learn how to use this feature go to Teacher Tips.
This will enable you to magnify areas across subduction zones.
World Seismicity Maps
http://earthquake.usgs.gov/regional/world/seismicity/
Assessment


Examine and describe the pattern of earthquake depths along and across subduction
zones.
Is this pattern present across midocean ridges? Explain your answer?
Step 2
Select the Australia, Indonesia and New Zealand map. This will give you a more detailed picture of
the pattern of earthquakes across active plate boundaries around the Australian plate.
World Seismicity Maps
http://earthquake.usgs.gov/regional/world/seismicity/
Activity
Examine the map and the pattern of earthquakes at the plate boundaries. Based on the evidence of the
depths of earthquakes identify the direction of plate motion at each plate boundary surrounding Australia
and describe it.
World Seismicity Maps
http://earthquake.usgs.gov/regional/world/seismicity/australia.php
Activity
1. Choose another area you can identify as a subduction zone and establish the direction of plate
motion based on earthquake depth at that subduction zone. Collaborate with other students to
determine the direction of plate motion of as many plates as you can based on the evidence of
earthquake distribution and depth.
2. Download or obtain a print copy of a world map and draw on the map the location of plate
boundaries you can identify from earthquake data and your best guess of plate motion at those
boundaries based on the evidence you have collected. Annotate your map with reasons for the
plate motion you are suggesting. A good physical map of the world can be downloaded at
http://www.mygeo.info/karten/802802.jpg . This map can then be manipulated, drawn on and
annotated in Photoshop.