2 FaultA break in Earth’s lithosphere (crust) where plates slide or move past each other.
3 Focus Focus: the starting point of an earthquake, usually underground Depth of the focus is related to the type of boundary.Transform: Shallow <300mDivergent: 300mSubduction: Deep 700m
4 EpicenterThe point directly above the focus on the surface of the Earth is called the Epicenter.
5 Seismic WavesVibrations caused by the energy of the earthquake that travel through the Earth’s interior and across the surface away from the focusP-WavesS-WavesSurface Waves
6 Primary Waves First Wave to Arrive Passes through… Squeeze and stretch rock, (Accordion-like)Compression / tension stressPasses through…Solid rockMagmaOcean waterAirEverything!
7 Secondary Waves Arrive second, after P-waves Vibrate from side to side, up and downShake the ground back and forthCan not pass through liquids or gassesIndicates that Earth has a liquid outer core.
8 Surface Waves Travel along the Earth’s surface Produced by P and S waves that reach the surfaceProduce severe ground movementMost damaging waves.
9 SeismographAn instrument used to detect and record the seismic waves produced by earthquakes.
10 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.
11 SeismogramThe record sheet the pen records on as the drum rotates.
12 Seismograph More than 10,000 Stations Use Data to… Determine an epicenterNeed 3 StationsEarthquake Magnitude
13 Locating an Epicenter r Need 3 Seismograph stations to determine their distance from the epicenterDetermine distance by:D = S-wave arrival time - P-wave arrival time.r
14 Locating an Epicenter Each station draws a circle. Where all three intersect is the epicenter.
15 MagnitudeThe measure of the amount of energy released in an earthquakeThree typesMercalliRichter ScaleMoment Magnitude.
16 Mercalli Scale12 steps describe how earthquakes effect people, buildings, and the surfaceRates earthquakes according to damage dealt to people and structuresNot a precise measurement.
17 Richter Scale Developed in the 1930’s by Charles Richter Rates the size of the seismic waves.Measures the intensity of ground movementsProvides accurate measurements for small, nearby earthquakes, but does not work well for large or distant.
20 Moment Magnitude Total Energy MM = Indicates the total energy released during earthquake’s more accuratelyScale used by scientistsCan be used for any size earthquake, near or far.Total EnergyMM=
21 Moment MagnitudeCombines the following to determine the moment magnitude:The type of seismic waves produced and their strengthHow much movement occurred on the faultStrength of the rocks that broke5.0 Little damageAbove 5.0 major damage
23 The point under the surface directly where the Earthquake originates is… A. FaultB. Seismic WavesC. Earth’s CrustD. FocusE. Epicenter
24 The point on the surface above where the Earthquake originates. A. FaultB. Seismic WavesC. Earth’s CrustD. FocusE. Epicenter
25 The wave that arrives first is the… A. Secondary WaveB. Seismic WavesC. Sound WaveD. Primary WaveE. Tsunami Wave
26 The scale that measures the total energy released is the… A. Richter ScaleB. Mecallie ScaleC. Bathroom ScaleD. Moment MagnitudeE. Magnitude
27 How many seismograph stations are needed to locate an earthquake? B. 3C. 1D. 6E. 4
28 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
29 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.
30 Locating an Epicenter Lab Seismograph Data:CityDenver, COHouston, TXMiami, FLDifference in P & S Wave Arrival Times2min 10sec4min5min 40sec