About Earthquakes
What Causes an Earthquake?
Unlike many other areas where a shift in tectonic
plates is the sole cause of an earthquake, 95% of earthquakes
in Hawaii are linked to volcanic activity. These earthquakes can
occur before or during eruptions, or as molten rock travels underground.
How is an earthquake measured?
Earthquakes are generally measured in terms of magnitude
and intensity.
The Richter Scale measures magnitude. An earthquake
of 5.0 is a moderate event, 6.0 is a strong event, 7.0 is a major
earthquake, and a "great quake" exceeds 8.0. For each whole number
increase there is a 10-fold jump in seismic wave amplitude (or,
a 30-fold gain in energy released). For example, a 6.0 earthquake
generates 30 times more energy than a 5.0 quake and 900 times
(30*30) greater than a 4.0 earthquake.
In the United States, the Modified Mercalli Intensity
Scale (MMI) measures intensity - the effects of an earthquake
felt by people. MMI ranges from I (faintly registered by instruments)
to XII (nearly total destruction). Ratings decrease with increasing
distance away from an earthquake's source.
Seismic Hazard Zones In Maui
County
It is difficult to assign earthquake hazard zones
to Hawaii because ground-shaking during an earthquake varies within
a small area, depending on the nature of the underlying ground
(e.g., lava bedrock or soil). Local topography also affects earthquake
hazards. Steep slopes composed of loose material may produce large
landslides during an earthquake. The type of construction also
affects the risks of damages to a property. For these reasons,
earthquake hazards are highly localized and difficult to assign
regional earthquake boundaries that share the same relative degree
of hazard.