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**Inside Earth Chapter 2.2 Pages 64-70**

Measuring Earthquakes Inside Earth Chapter 2.2 Pages 64-70

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

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**Focus Focus: the starting point of an earthquake, usually underground**

Depth of the focus is related to the type of boundary. Transform: Shallow <300m Divergent: 300m Subduction: Deep 700m

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

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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

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**Primary Waves First Wave to Arrive Passes through…**

Squeeze and stretch rock, (Accordion-like) Compression / tension stress Passes through… Solid rock Magma Ocean water Air Everything!

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**Secondary Waves Arrive second, after P-waves**

Vibrate from side to side, up and down Shake the ground back and forth Can not pass through liquids or gasses Indicates that Earth has a liquid outer core.

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**Surface Waves Travel along the Earth’s surface**

Produced by P and S waves that reach the surface Produce severe ground movement Most damaging waves.

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Seismograph An instrument used to detect and record the seismic waves produced by earthquakes.

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**Seismograph Consists 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.

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Seismogram The record sheet the pen records on as the drum rotates.

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**Seismograph More than 10,000 Stations Use Data to…**

Determine an epicenter Need 3 Stations Earthquake Magnitude

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**Locating an Epicenter r**

Need 3 Seismograph stations to determine their distance from the epicenter Determine distance by: D = S-wave arrival time - P-wave arrival time. r

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**Locating an Epicenter Each station draws a circle.**

Where all three intersect is the epicenter.

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Magnitude The measure of the amount of energy released in an earthquake Three types Mercalli Richter Scale Moment Magnitude.

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Mercalli Scale 12 steps describe how earthquakes effect people, buildings, and the surface Rates earthquakes according to damage dealt to people and structures Not a precise measurement.

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**Richter Scale Developed in the 1930’s by Charles Richter**

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.

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Richter Scale

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Richter Scale

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**Moment Magnitude Total Energy MM =**

Indicates the total energy released during earthquake’s more accurately Scale used by scientists Can be used for any size earthquake, near or far. Total Energy MM =

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Moment Magnitude 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

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Moment Magnitude

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**The point under the surface directly where the Earthquake originates is…**

A. Fault B. Seismic Waves C. Earth’s Crust D. Focus E. Epicenter

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**The point on the surface above where the Earthquake originates.**

A. Fault B. Seismic Waves C. Earth’s Crust D. Focus E. Epicenter

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**The wave that arrives first is the…**

A. Secondary Wave B. Seismic Waves C. Sound Wave D. Primary Wave E. Tsunami Wave

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**The scale that measures the total energy released is the…**

A. Richter Scale B. Mecallie Scale C. Bathroom Scale D. Moment Magnitude E. Magnitude

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**How many seismograph stations are needed to locate an earthquake?**

B. 3 C. 1 D. 6 E. 4

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**What to Work On DUE: Friday, October 21st Read textbook pages 64-69**

Answer the Section Review questions on page 69 (#’s 1-4) DUE: Friday, October 21st

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**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.

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**Locating an Epicenter Lab**

Seismograph Data: City Denver, CO Houston, TX Miami, FL Difference in P & S Wave Arrival Times 2min 10sec 4min 5min 40sec

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**Locating an Epicenter Lab**

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**Locating an Epicenter Lab**

(km)

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