![](img009.GIF) |
This means that we have to understand two
factors that characterize impact. Magnitude is an absolute measurement of
the size and power of an event. When we speak of a Moment Magnitude 6.5
earthquake, a Category IV hurricane, an old Fujita 3 tornado, a 70,000
barrel oil spill, or a railway accident that kills 152 persons, we are
attributing magnitude to the event. Intensity is a measurement of how the
effects of the event are felt in a specific place. To some degree the
Saffir-Simpson (hurricane) and Fujita (tornado) scales do this in that they
provide descriptions of the levels of damage and effects that will occur at
the point of greatest impact. However, the most commonly used intensity
scale is probably the Modified Mercalli Intensity scale for earthquakes.
This scale allows the plotting of lines of equal intensity in earthquakes,
characterizing the extent of impact within these lines. |