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Measuring Earthquakes
How are earthquakes measured?
Seismology
The study of earthquake waves is called Seismology
Earthquake waves can be detected at great distances by Seismometers
A seismometer’s record is known as a seismogram
Time-Travel Curves
Years of data collection has led to time-travel curves
The curves tell the time an S- and P-wave takes to reach a certain distance
P-waves arrive first The difference between waves on a
seismogram determines the distance from the epicenter
Time-Travel Curves
Locating Earthquakes
Epicenters are located by the separation between S- and P-waves on a seismogram
Cannot use one location to map epicenter
Need to use three or more seismic stations
Time can be measured in same way
Earthquake Intensity
The amount of energy released during an earthquake is known as its magnitude
Three scales measuring intensity Richter Scale Moment Magnitude Scale Modified Mercalli Scale
Richter Scale
The Richter Scale is based on the largest waves generated by the quake
Each number on the scale is an increase of 10 Ex: 8 is 10x larger than 7, 100x larger than 6
Moment Magnitude Scale
The Moment Magnitude Scale includes: Size of fault rupture Amount of movement along fault Rocks’ stiffness
Uses more data than Richter Scale – More accurate
Modified Mercalli Scale
The Modified Mercalli Scale assesses damage from a quake
Factors affecting Magnitude
Distance from epicenter
Depth of focus
Where do Earthquakes Occur?
Earthquakes are not randomly distributed Almost 80% of Earthquakes occur along the
Circum-Pacific Belt