Earthquake Scales Measuring Earthquakes 3 d Students know

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

• More than 1 million earthquakes occur each year • More than 90% of earthquakes are not felt and cause little to no damage Average Annually Magnitude 8 and higher 1¹ 7 - 7. 9 15 ¹ 6 - 6. 9 134 ² 5 - 5. 9 1319 ² 4 - 4. 9 13, 000 (estimated) 3 - 3. 9 130, 000 (estimated) 2 - 2. 9 1, 300, 000 (estimated)

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

34, 359, 738, 368 1, 073, 741, 824 33, 554, 432 1, 048, 576 32, 768 1024

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 180 mm

Large Amplitudes imply: • Earthquake epicenter is very close • Earthquake is far away but very large

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)

What does Intensity depend on? a) Amplitude of Surface Waves • Most damage typically occurs in the region nearest the epicenter b) Depth of Focus • Shallow – closer to surface • Deep – further from surface

c) Types of Soil • Solid rock – least damage • Moderately consolidated soil (clay, sand) – intermediate damage • Unconsolidated soil (loose, not compact) – most damage

• Mercalli scale data is used to make seismic intensity maps