1. “Measuring Earthquakes”
Earthquake Scales
“Measuring Earthquakes”
3d - Students know why and how earthquakes occur and the scales used to measure their intensity and magnitude.

2. More than 1 million earthquakes occur each year
More than 90% of earthquakes are not felt and cause little to no damage
Magnitude
Average Annually
8 and higher
1 ¹
15 ¹
134 ²
1319 ²
13,000 (estimated)
130,000 (estimated)
1,300,000 (estimated)

3. The Richter Scale Charles Richter (1935)
Measures Magnitude (energy released)
Scale ranges from 1 – 10
Each increase in magnitude is 10 times stronger than the previous number (shaking strength)
Each increase in magnitude is 32 times the amount of seismic energy than the previous number
A wave one millimeter (1000 microns) high on a seismogram would have a magnitude of 3 because 1000 is ten raised to the third power. In contrast, a wave ten millimeters high would have a magnitude of 4. For reasons that we won't go into, a factor of 10 change in the wave height corresponds to a factor of 32 change in the amount of energy released during the earthquake. In other words, a magnitude 7 earthquake would produce seismogram waves 10 x 10 = 100 times as high and release energy 32 x 32 = 1024 times as great as a magnitude 5 earthquake.

5. 327 = 34,359,738,368
326 = 1,073,741,824
325 = 33,554,432
324 = 1,048,576
323 = 32,768
322 = 1024
321

7. Size of Amplitude depends on:
Distance from epicenter
Magnitude of the earthquake
Based on the amplitude of the largest seismic wave recorded on a seismogram
Amplitude is measured in millimeters (mm) from the center of the seismic record to the maximum on the trace.
In this case the amplitude is
Amplitude is measured in millimeters (mm) from the center of the seismic record to the maximum on the trace.
In this case the amplitude is 180 mm (you can also measure the maximum width of the trace and divide by 2.
180 mm

8. Large Amplitudes imply: Earthquake epicenter is very close
Earthquake is far away but very large
Richter scale is logarithmic

14. The Mercalli Scale I on end for Intensity! Measures Intensity (damage)
Uses roman numerals from I to XII (1 = low intensity and 12 = high intensity)

15. What does Intensity depend on?
Amplitude of Surface Waves
Most damage typically occurs in the region nearest the epicenter
Depth of Focus
Shallow – closer to surface
Deep – further from surface
A deep-focus earthquake produces smaller vibrations at the epicenter than a shallow-focus quake because it occurs further from the surface.

16. Solid rock – least damage
Types of Soil
Solid rock – least damage
Moderately consolidated soil (clay, sand) – intermediate damage
Unconsolidated soil (loose, not compact) – most damage
Left seismogram = soft soils
Right seismogram = harder rock

17. Mercalli scale data is used to make seismic intensity maps