earthquakes and seismic waves. earthquake: shaking and trembling that results from the movement of...

Earthquakes and Earthquakes and Seismic WavesSeismic Waves

Earthquakes and Seismic Earthquakes and Seismic WavesWaves

Earthquake:•Shaking and trembling that results from the movement of rock beneath Earth’s surface.•The forces of plate movement cause earthquakes.•Stress increases along a fault until the rock breaks- resulting in an earthquake.


Building DamageRoad Damage

House Damage Bridge Damage


• The focus is the area BENEATH Earth’s surface where rock that is under stress breaks• The epicenter is the point on the SURFACE DIRECTLY ABOVE the focus.


Seismic Waves:•Vibrations that travel through Earth •Carry energy from an earthquake away from the focus, through the Earth’s interior, and across the surface.•3 main categories: P waves, S waves and surface waves.


Primary Waves (P waves):•First waves to arrive•Can travel through liquids AND solids•Pushes and pulls materials as they move through earth•2 important terms to describe P waves:

1. Compression: The compressed part of the wave. It’s the name of the region where the coils of the slinky are pushed together.

2. Rarefaction: The spread out part of the wave. As the wave travels, rarefactions takes turns with compressions. It’s the name of the region where the coils of the slinky are pulled apart.


http://www.youtube.com/watch?v=2rYjlVPU9U4

http://www.edinformatics.com/math_science/transverse_longitudinal_waves.htm




Secondary Waves (S waves);•S waves arrive second after P waves•Travels through solids ONLY•Vibrates side to side as well as up and down•Shakes structures violently•3 important terms to describe S waves:

1. Crest: The highest part of an S wave. 2. Trough: The lowest part of an S wave. 3. Amplitude: the distance from the middle

of the wave straight up to the top of a crest or straight down to the bottom of a trough


http://www.edinformatics.com/math_science/transverse_longitudinal_waves.htm

http://www.youtube.com/watch?v=en4HptC0mQ4


Surface Waves:•Moves more slowly than P waves and S waves•Produce severe ground movements•Makes the ground roll like ocean waves.•Shakes buildings from side to side.•Most destructive


• P Waves go through solids and liquids

• S Waves go through solids ONLY


Measuring Earthquakes:•Magnitude is a number that geologists assign to an earthquake based on the earthquake’s size.•Geologists determine magnitude by measuring the seismic waves and fault movement.•2 ways of measuring earthquakes – Richter Scale and Mercalli Scale


Richter Scale:•Rating of an earthquake’s magnitude based on the size of the earthquake’s seismic waves.•Here, the waves are measured by a seismograph•Provides accurate measurements for small, nearby earthquakes•Does not work well for large or distant earthquakes


Mercalli Scale:•Rates earthquakes according to the level of damage•12 steps that describe an earthquake’s effects•same earthquake can have different ratings due to different amounts of ground motion at different locations.•Uses Roman numerals to rank how much damage is caused


Locating the Epicenter:•Geologists use seismic waves to locate the epicenter•P waves arrive at a seismograph station first, with S waves following second•The difference between the arrival time of P waves and S waves is measured•Geologists draw three circles using data from different seismographs stations.•The center of each circle is the seismograph stations location•The radius of each circle is the distance from that seismograph station to the epicenter


Look at the diagram below – the point where the three circles intersect is the location of the epicenter.


Where do you see the epicenter?


Where do you see the epicenter?

http://www.youtube.com/watch?v=694yaY2ylTg


Seismograph: •A device that records ground movements caused by seismic waves as they move through earthHow does a Seismograph work?•a heavy weight attached to a frame by wire•A pen connected to the weight, rests its point on a rotating paper drum•As the paper drum rotates slowly the pen draws a straight line•Seismic waves cause the drum to vibrate, while the pens records the drum’s vibrations•http://www.youtube.com/watch?v=83GOKn7kWXM


This is what P waves, S waves and Surface waves look like on a seismograph.

earthquakes and seismic waves. earthquake: shaking and trembling that results from the movement of...

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