MeasuringMeasuring

CH 5 Prentice Hallp.154-159

CH 5 Prentice Hallp.154-159

EarthquakesEarthquakes

Fault

• A break in Earth’s lithosphere (crust) where plates slide or move past each other.

Earthquake (Focus)

• The point of first movement (where the earthquake originates) usually underground is called the Focus.– Depth of the focus is related to the type of

boundary.• Subduction- Deep 700m• Divergent- 30m• Transform- Shallow

Earthquake (Epicenter)

• The point directly above the focus on the surface of the Earth is called the Epicenter.

Seismic Waves

• Vibrations caused by the energy of the earthquake that travel through the Earth’s interior and across the surface away from the focus.– P-Waves– S- Waves– Surface Waves

• .

Primary Waves

• First Wave to Arrive– Squeeze and stretch rock, (Accordion like)• Compressional Push/Pull

– Pass through• Solid rock• Magma• Ocean water• Air

Secondary Waves

• Arrive second after P-waves– Vibrate from side to side as well as up and down.– Shake the ground back and forth.– Can not pass through liquids or gasses.• Indicates that Earth has a liquid outer core.

Surface Waves

• Travel along the Earth’s surface• Produced by S and P waves that reach the

surface.– Produce severe ground movement• Most damaging waves

Locating an Epicenter Lab

• Purpose: Geologists who study earthquakes are called seismologists. If you were a seismologist, you would receive data from all across the country. Within minutes after an earthquake, seismographs located in Denver, Houston, and Miami would record the times of arrival of the P waves and S waves. You would use this data to zero in on the exact location of the earthquake’s epicenter.

Locating an Epicenter Lab

CityDenver,

COHouston,

TXMiami,

FLDifference in P & S

Wave Arrival Times

2min 10sec 4min 5min 40sec

• Seismograph Data:

Locating an Epicenter Lab

Locating an Epicenter Lab

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600 4800 5000 (km)

Seismograph

• An instrument used to detect and record waves produced by earthquakes.– seismic waves.

Seismograph

• Consist of a heavy weight attached to a frame by a wire.

• A pen is attached to a heavy weight.

• The pen stays in place, the drum moves during an earthquake.

Seismograph

• More than 10,000 Stations• Use Data to :– Determine an epicenter• Need 3 Stations

– Earthquake Magnitude

Seismogram

• The record sheet the pen records on as the drum rotates.– No movement=– Movement =

Locating an Epicenter

• Need 3 Seismograph stations to determine their distance from the epicenter.

• Determine distance by:– Dist = S-wave arrival time - P-wave arrival time.

Locating an Epicenter

• Each station draws a circle.– Where all three intersect is the epicenter.

• The measure of the amount of energy released in an earthquake.

– Three types• Mercalli• Richter Scale Magnitude – most commonly used• Moment Magnigude

Layers of

Earth Menu

Magnitude

• Rates earthquakes according to intensity. (the strength of the ground movement)

• Not a precise measurement

• 12 steps describe how earthquakes effect people, buildings, and the surface.

Mercalli Scale

Layers of

Earth Menu

• Developed in the 1930’s• Rates the size of the seismic waves.• Measures the intensity of ground movements– Provides accurate measurements for small,

nearby earthquakes, but does not work well for large or distant.

Richter Scale

Layers of

Earth Menu

Layers of

Earth Menu

Richter Scale

• Indicates the total energy released during earthquake’s more accurately.

• Used today.• can be used for any size earthquake, near or

far.

Moment Magnitude

Layers of

Earth Menu

• Combines the following to determine the moment magnitude:– The type of seismic waves produced and their

strength.– How much movement occurred on the fault.– Strength of the rocks that broke.• 5.0 Little damage• Above 5.0 major damage

Moment Magnitude

Layers of

Earth Menu

Layers of

Earth Menu

E. EpicenterE. Epicenter

A. FaultA. Fault

B. Seismic WavesB. Seismic Waves

C. Earth’s CrustC. Earth’s Crust

D. FocusD. Focus

The point under the surface directly where the Earthquake originates.

Layers of

Earth Menu

This scale measures total energy released.

E. MagnitudeE. Magnitude

A. Richter ScaleA. Richter Scale

B. Mecallie ScaleB. Mecallie Scale

C. Bathroom ScaleC. Bathroom Scale

D. Moment MagnitudeD. Moment Magnitude

Layers of

Earth Menu

How many seismograph stations are needed to locate an

earthquake?

E. 4E. 4

A. 5A. 5

B. 3B. 3

C. 1C. 1

D. 6D. 6

Layers of

Earth Menu

The wave that arrives first

E. Tsunami WaveE. Tsunami Wave

A. Secondary WaveA. Secondary Wave

B. Seismic WavesB. Seismic Waves

C. Sound WaveC. Sound Wave

D. Primary WaveD. Primary Wave

Layers of

Earth Menu

The point on the surface directly above where the Earthquake

originates.

E. EpicenterE. Epicenter

A. FaultA. Fault

B. Seismic WavesB. Seismic Waves

C. Earth’s CrustC. Earth’s Crust

D. FocusD. Focus