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