This graph shows earthquakes that have happened in the past four days (approximately). 

The graph you are currently viewing (that is hidden by this help information) is showing the
total magnitude of recent earthquakes.

You can experiment with other ways of viewing this earthquake information by clicking on
the four different menu options to the left and top of the graph:

Data to Graph - Change this to be 'Number of Quakes' to see how many earthquakes
ocurred, to 'Total Strength' to see the absolute strengths of the earthquakes that
happened, or to 'Total Magnitude' to the sizes of earthquakes on the Ritcher scale.

Graph Style - This menu item allows you to see either the raw information (first option),
earthquakes, or to choose between two different ways of examining the trend over time.