Measuring Earthquakes

Seismograph

• Or seismometer, is an instrument used to detect and record earthquakes.

Seismogram

• A record written by a seismograph in response to ground motions produced by an earthquake, explosion, or other ground-motion sources.

Seismogram

• A record written by a seismograph in response to ground motions produced by an earthquake, explosion, or other ground-motion sources.

Amplitude

• The size of the wiggles on an earthquake recording.

P or Primary Waves

• The fastest type of seismic waves, can travel through liquid and solids. This is a body wave.

S or Secondary Waves

• The second fastest type of seismic wave; cannot travel through materials that are liquid. This is a body wave.

Body Waves

Surface Waves

• Move the ground roll up and down or shake from side to side as the waves travel along the surface. These cause the most destruction. P and S waves can turn into surface waves.

Richter Scale

Richter Scale

• Video:

• What scale do scientist use to measure the magnitude of an earthquake today? answer

Moment Magnitude Scale

• Video

• The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped.

Vocabulary

• Richter Scale & Moment Magnitude Scale (MMS): A quantitative (objective) measure of strength – how much energy the earthquake releases. MMS is the most accurate with 3.5 and higher quakes.

• Magnitude = size or amount of energy released

How many magnitudes

• Can there be for one specific earthquake?

A different type of scale

• For measuring the intensity of an earthquake

Modified Mercalli Scale

• Mercalli Intensity Scale: A qualitative (subjective) measure of earthquake’s effect on area – a measure of intensity.

• Magnitude vs. Intensity