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