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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.
Instead of just displaying the points normally on the graph, what you see below is
a 'smoothed' graph. This means that we have tried to place the points on the graph
into a smooth curve. This shows us the overall trend of earthquakes over time. If
earthquakes have increased for several hours in a row, the line will start to curve
upwards. If earthquakes have decreased for several hours in a row, the line will start
to curve downwards.
(Note that this form of analysis is much less reliable on hourly earthquake information.)
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.