scales that represent earthquake magnitude

measuring earthquakes

People have always tried to quantify the size of and damage done by earthquakes. Since early in the 20th century, there have been three methods. What are the strengths and weaknesses of each?

mercalli intensity scale

Earthquakes are described in terms of what nearby residents felt and the damage that was done to nearby structures. What factors would go into determining the damage that was done and what the residents felt in a region?

moment magnitude scale is best

Which scale do you think is best? With the Richter scale, a single sharp jolt measures higher than a very long intense earthquake that releases more energy. The moment magnitude scale more accurately reflects the energy released and the damage caused. Most seismologists now use the moment magnitude scale. The way scientists measure earthquake intensity and the two most common scales, Richter and moment magnitude, are described in the video below. Click image to the left or use the URL below. URL:

log scales

The Richter scale and the moment magnitude scale are logarithmic scales. The amplitude of the largest wave increases ten times from one integer to the next. An increase in one integer means that thirty times more energy was released. These two scales often give very similar measurements. How does the amplitude of the largest seismic wave of a magnitude 5 earthquake compare with the largest wave of a magnitude 4 earthquake? How does it compare with a magnitude 3 quake? The amplitude of the largest seismic wave of a magnitude 5 quake is 10 times that of a magnitude 4 quake and 100 times that of a magnitude 3 quake. How does an increase in two integers on the moment magnitude scale compare in terms of the amount of energy released? Two integers equals a 900-fold increase in released energy.

moment magnitude scale

This scale measures the total energy released by an earthquake. Moment magnitude is calculated from the area of the fault that is ruptured and the distance the ground moved along the fault.

richter magnitude scale

Developed in 1935 by Charles Richter, this scale uses a seismometer to measure the magnitude of the largest jolt of energy released by an earthquake.

instructional diagrams

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questions

this scale is based on the strength of an earthquake by the damage done.

a) richter magnitude

b) moment magnitude

c) seismic scale

-->  d) mercalli intensity

what is the similarity between the richter scale and moment magnitude scale to measure an earthquake?

-->  a) both can measure all types of earthquakes.

b) both measure the total energy released.

c) both measure the largest jolt of energy released.

d) both measure the damage done.

there is not too much difference in magnitude of an earthquake between a 7.5 and an 8.5.

a) true

-->  b) false

this scale measures the total amount of energy released by an earthquake.

a) richter magnitude

-->  b) moment magnitude

c) seismic scale

d) mercalli intensity

the best scale to measure an earthquake is the mercalli scale.

a) true

-->  b) false

a scale in which each unit is an exponential increase over the previous unit.

a) richter

b) moment magnitude

-->  c) logarithmic

d) mercalli

how much more energy released in a moment magnitude quake of 8 than a 6?

a) 10 times

b) 30 times

c) 100 times

-->  d) 900 times

this scale measures an earthquake by the largest jolt made.

-->  a) richter magnitude

b) moment magnitude

c) seismic scale

d) mercalli intensity

the amplitude of the largest seismic wave of a magnitude 5 quake is 100 times that of a magnitude 4 quake.

a) true

-->  b) false

under what circumstances would the richter scale give a greater magnitude to a quake than the magnitude moment scale?

a) if there was more energy released.

b) if there was more damage done.

c) if the energy was released in jolts rather than a steady stream.

-->  d) if the quake had a single sharp jolt but otherwise did not release as much energy.

diagram questions

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