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Term | Definition |
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Magnitude |
Related to the amount of energy released during an earthquake. It is determined from parameters of the seismic waves recorded on seismographs e.g. amplitude, period, duration. A magnitude of 7.0 on the Richter Scale is a major earthquake. Each whole number on the scale represents an increase of about 10 times more energy released than the previous whole number represents. Therefore, an earthquake measuring 7.0 is about 100 times more powerful than one measuring 5.0. |
Mangrove Forest |
A community of salt-tolerant trees and shrubs, with many other associated organisms that grows on some tropical and sub-tropical coasts in a zone roughly coinciding with the intertidal zone. |
Mean Height |
Average height of a tsunami measured from the trough to the crest after removing the tidal variation. |
Mean High Water (MHW) |
The average height of the high water over a 19-year period. For shorter periods of observations, corrections are applied to eliminate known variations and reduce the results to the equivalent of a mean 19-year value. All high water heights are included in the average where the type of tide is either semi-diurnal or mixed. |
Mean Low Water (MLW) |
The average height of the low water over a 19-year period. For shorter periods of observations, corrections are applied to eliminate known variations and reduce the results to the equivalent of a mean 19-year value. All low water heights are included in the average where the type of tide is either semi-diurnal or mixed. |
Mean Sea Level (MSL) |
The average height of the surface of the sea for all stages of the tide over a 19-year period, usually determined from hourly height readings. Not necessarily equal to mean tide level. It is also the average water level that would exist in the absence of tides. |
Mean Tide Level |
A plane midway between mean high water and mean low water. Not necessarily equal to mean sea level. Also referred to as half-tide level. |