EARTHQUAKES! Video: Earthquakes 101 Chapter 12

Section 1 Earthquakes are caused by a sudden release of energy when rocks move along a fault. Elastic rebound is thought to cause the rocks to move.

Anatomy of an Earthquake Focus-location of first motion in Earth Epicenter-spot on surface above the focus The focus can be shallow or deep Shallow foci cause the most damage

Seismic Waves Body Waves: Travel through the Earth Made up of: -P waves: primary, fastest -S waves: secondary, second fastest, travel through solids only

Earthquake Waves & Earth’s Interior

Seismic Waves and the Earth’s Interior The speed and direction of seismic waves gives us information about the Earth’s structure Waves travel at different speeds through different materials Shadow Zones-areas where no body waves are detected

Comparing Seismic Waves

Seismic Waves (cont) Surface Waves Slowest moving waves May cause the greatest damage 2 Types: -Rayleigh -Love

Earthquakes and Plate Tectonics Most earthquakes occur at plate boundaries (converging and diverging) where the stress is the greatest

How Seismographs or Seismometers Work, TB pg. 217 -measures ground motion and can be used to determine the distance seismic waves travel https://www.youtube.com/watch?v=Gbd1FcuLJLQ http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

They use the lag time to calculate a distance to the epicenter How do scientists calculate how far a location is from the epicenter of an earthquake? Scientists calculate the difference between arrival times of the P waves and S waves (lag time) The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves They use the lag time to calculate a distance to the epicenter

Typical Seismogram- a graphical illustration of EQ waves http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Section 2 Seismographs record vibrations in the ground Magnitude: the strength of an earthquake, Richter scale or moment magnitude (more accurate) Intensity (amount of damage)-modified Mercalli scale-from I-XII, oldest measurement scale

How are Earthquakes Measured? Richter Scale

How are Earthquakes Measured? Mercalli Intensity Scale Click on the picture for a video clip Or Simulator link

Predicting Earthquakes-video clip: https://www. youtube. com/watch No reliable way to predict earthquakes: scientist use the following information Scientists are trying to detect changes that occur before an earthquake Seismic gaps are areas of low earthquake activity, but have a history of strong activity-might be spot for future earthquake Foreshocks-small earthquakes that precede a large earthquake

Soil Type *Type A having the least amplification and Type E the most. Type of soil can affect how a building responds to seismic waves. NEHRP has defined six different soil and rock types based on their shear-wave velocity, in order to determine amplification effects: Type A, hard rock (igneous rock). Type B, rock (volcanic rock). Type C, very dense soil and soft rock (sandstone). Type D, stiff soil (mud). Type E, soft soil (artificial fill). *Type A having the least amplification and Type E the most.

Section 3 Video: Tsunamis 101 Tsunamis can form when the epicenter is on the ocean floor Damage to structures depends on how they are built and what type of ground they sit on