We now have a map showing two weeks of seismic activity in southern California immediately following the Landers mainshock. To turn this into a useful diagram for our blink comparison, we will have to remove all those epicenters that can be considered aftershocks of the Landers and Big Bear earthquakes. To do that, we need to designate an "aftershock zone".
First, find the epicenters of the Landers and Big Bear earthquakes. They are the two partially "transparent" circles in the huge mass of overlapping epicenter symbols. Now, note that the epicenters around them -- their aftershocks -- form a continuous "mass" of circles on the map. A good way to designate an aftershock zone would be to simply outline this continuous cluster of epicenters, and any nearby epicenters that fall inside this general area. This will be done for you when you move your mouse over the box labelled "Draw outline now". To see the map without the outline, move your mouse over the box labelled "Remove outline". When you're ready to move on, click either box, or the map itself, to continue.
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