Measuring CH 5 Prentice Hall p CH 5 Prentice Hall p Earthquakes

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 City Denver, CO Houston, TX Miami, FL Difference in P & S Wave Arrival Times 2min 10sec4min5min 40sec Seismograph Data:

Locating an Epicenter Lab

(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. Epicenter A. Fault B. Seismic Waves C. Earth’s Crust D. Focus The point under the surface directly where the Earthquake originates.

Layers of Earth Menu This scale measures total energy released. E. Magnitude A. Richter Scale B. Mecallie Scale C. Bathroom Scale D. Moment Magnitude

Layers of Earth Menu How many seismograph stations are needed to locate an earthquake? E. 4 A. 5 B. 3 C. 1 D. 6

Layers of Earth Menu The wave that arrives first E. Tsunami Wave A. Secondary Wave B. Seismic Waves C. Sound Wave D. Primary Wave

Layers of Earth Menu The point on the surface directly above where the Earthquake originates. E. Epicenter A. Fault B. Seismic Waves C. Earth’s Crust D. Focus