Tectonics Measuring Flashcards
Mercalli Scale
I - XII
Measures the experienced impacts of an earthquake.
relative scale because people
experience different amounts of shaking in different
places.
3: Tremors or noticed by many often do not realise it is an earthquake
6 felt by all many people running outdoors. Furniture is moved
10 many structures, were destroyed, ground badly cracked
12 total destruction Waves seen at ground surface
BUT:
stronger the magnitude of an earthquake the higher the intensity, but local conditions may modify this correlation through secondary hazards
no use for remote area or under ocean
Richter Scale
Richter scale, one to 10 logarithmic
the arrival times of the P and S waves, the amplitude of the S wave, and the distance from the
epicentre. A measurement of the height (amplitude) of the
waves produced by an earthquake.
Absolute Measure not relative
4-5 is lights 5 - 6, moderate, 6-7, strong, 7-8, major, 8-9 great
BUT
quantitative scale, being based on numerical measurement - impacts dep on human side as well
The magnitude becomes unreliable for measurements taken at a distance of more than about 600 kilometres from the epicentre.
Moment Magnitude
Scale (MMS)
0-9
describe earthquakes in terms of energy released. the amount
of slip on the fault, the areas affected and an Earth–
rigidity factor.
EVAL:
more accurate than the Richter Scale as it
uses the energy released by all shockwaves as well as
the area of rupture and movement.
there is no upper
limit to the possible measurable magnitudes - so scale may diverge for smaller eqs
VEI
0-8 Volc Eruption - logarithmic
a relative measure of the explosiveness of a volcanic
eruption, which is calculated from the volume of products (ejecta), the height of the eruption cloud and
qualitative observations.
EVAL
more difficult when the
eruption occurs in a remote area
estimation problems occur in calculating ejecta
volumes for ancient eruptions.
