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# Measuring & Locating Quakes - PowerPoint PPT Presentation

Measuring & Locating Quakes. Measuring and Locating Earthquakes. Objectives. Compare and contrast earthquake magnitude and intensity and the scales used to measure each. . Explain why data from at least three seismic stations are needed to locate an earthquake’s epicenter.

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### Measuring & Locating Quakes

Objectives

• Compare and contrast earthquake magnitude and intensity and the scales used to measure each.

• Explain why data from at least three seismic stations are needed to locate an earthquake’s epicenter.

• Describe Earth’s seismic belts.

Vocabulary

• magnitude

• Richter scale

• movement magnitude scale

• modified Mercalli scale

Measuring and Locating Earthquakes

• More than one million earthquakes occur each year.

• More than 90 percent of earthquakes are not felt and cause little, if any, damage.

A. Measurement Scales

• 1. Richter Scale measures the magnitude of an earthquake.

• Each successive number in the scale represents an increase in seismic-wave size, or amplitude, of a factor of 10.

• Each increase in magnitude corresponds to about a 32-fold increase in seismic energy.

2. Moment Magnitude Scale

• The moment magnitude scale, takes into account the size of the fault, the amount of movement along the fault, and the rock type.

3. Modified Mercalli Scale

- measures in human terms. Uses Roman numerals I.-XII to indicate the size of a quake in terms of damage done. The same quake could register differently in different areas, depending on the quality of structures in the area.

Earthquake Magnitude and Intensity

B. Earthquake Magnitude and Intensity

Depth of Focus- deeper quakes usually have less of an impact on the Earth’s surface.

D. Seismic Belts

• The majority of the world’s earthquakes occur on or near plate boundaries.

• Almost 80 percent of all earthquakes occur in the Circum-Pacific Belt.

• About 15 percent take place across southern Europe and Asia.

• Most of the remaining earthquakes occur in narrow bands that run along the crests of ocean ridges.

• A very small percentage of earthquakes happen far from tectonic plate boundaries and are distributed more or less at random.

Seismic Belts