1. Inside Earth, Chapter 2, Section 2
Earthquakes
Inside Earth, Chapter 2, Section 2

2. Cause of Earthquakes Why do earthquakes occur?
An earthquake occurs when rocks break along a fault. This sudden release of energy causes seismic waves. The spot underground where the rock breaks is called the focus, and is deep in Earth’s crust.

3. Seismograph What is a seismograph? How does it work?
A device used to record the ground movements caused by seismic waves as they move through Earth.
How does it work?
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4. Three Types of Scales
There are three types of scales used to measure the magnitude/intensity of an earthquake:
Mercalli scale – not a precise measurement, describes how earthquakes affect people, buildings, and the land
Richter scale – was used when mechanical seismographs were used; measures earthquakes that are small and nearby

5. Scale Used Today Moment Magnitude Scale
Geologists use this today because it is the most accurate.
Estimates the total energy released by an earthquake.
Rates earthquakes of all sizes, near and far
article on high magnitude earthquakes
article about the Richter scale