Earthquakes and Seismic Waves

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.

Earthquakes and Seismic Waves Building Damage Road Damage House DamageBridge Damage

Earthquakes and Seismic Waves 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.

Earthquakes and Seismic Waves

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.

Earthquakes and Seismic 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.

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Earthquakes and Seismic Waves 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

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Earthquakes and Seismic Waves 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

Earthquakes and Seismic Waves P Waves go through solids and liquids S Waves go through solids ONLY

Earthquakes and Seismic Waves 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

Earthquakes and Seismic Waves 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

Earthquakes and Seismic Waves 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

Earthquakes and Seismic Waves 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

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

Earthquakes and Seismic Waves Where do you see the epicenter?

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Earthquakes and Seismic Waves Seismograph: A device that records ground movements caused by seismic waves as they move through earth How 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 GOKn7kWXM GOKn7kWXM

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