To start our construction of a proper "blink diagram" for this investigation, we need to start with a map of seismic activity from a standardized period of time after the Landers mainshock. For this example, we will use two weeks (14 days). Below is a background map of southern California, covering an area from 32° to 36° North latitude and from 114.75° to 121° West longitude. Some towns and major highways are shown. Three areas of fault rupture are depicted in reddish-orange. They represent the Landers earthquake and the Big Bear earthquake (an aftershock of the Landers earthquake), both of which struck on June 28, 1992, as well as the Joshua Tree earthquake of April 22. Aftershocks of the Joshua Tree earthquake were still occurring when the Landers earthquake happened. Only the Landers rupture broke through to the surface, so the other two ruptures are approximated, and shown with dashed lines. Below the map are two "control boxes" that you can use to change the image, as outlined below.
We will overlay symbols marking the epicenters of the first two weeks of earthquake activity immediately following the Landers mainshock -- that is, the activity in all of southern California for 14 continuous days, starting on June 28, 1992, at 4:53 am. When you are ready to overlay these symbols, move the mouse pointer over the control box that reads "Overlay epicenters". To remove these and see the "clean" background map, move the mouse over the box that reads "Restore background". When you're ready to move on, click on either box, or the map image itself.
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