CHAPTER 7 EARTHQUAKES

7.1 Notes What are earthquakes? earthquakes - movements or shaking of the ground when rock (plates) move suddenly and release energy. aftershock – a release in energy after an earthquake

Where do most earthquakes happen? On plate boundaries (page 232)

What causes earthquakes? Movement of the tectonic plates When the plates break at a fault located at a boundary

How do we know there are different layers of the Earth? Because of seismic waves from earthquakes Seismic waves travel through solids faster than liquids Seismic waves change direction when they change the material they are going through (from a solid to a liquid) elastic rebound – the sudden return of deformed rock to its normal undeformed shape. (i.e. rubber band)

7.1 Notes seismic waves – waves of energy that travel through and on the Earth 2 types of seismic body waves: 1. P-waves (primary waves) – the fastest seismic waves that travel through solids, liquids, and gases (the P-waves move like a slinky) 2. S-waves (secondary waves) – the second fastest seismic waves that travel through solids (the S-waves move like a snake) 1 type of seismic surface waves : 1. L-waves (land & last waves) – the slowest and most destructive seismic waves that travel only on the surface/land (the L-waves move in big slow circles)

7.2 Notes Earthquake Measurements epicenter – the point on the Earth’s surface directly above the earthquake’s starting point focus – the point inside the Earth where an earthquake begins

7.2 Notes seismograph – an instrument at or near the surface of the Earth that record seismic waves (machine) seismogram – is a tracing of earthquake motion created by a seismograph (paper)

How do you find an epicenter? 1. You need to find the S-P time difference and that is the distance from the seismograph to the epicenter. P-wave time minus the S-wave time 2. Draw a circle around the seismograph location. 3. Do this three times because you need three seismograph stations to find an epicenter. 4. Where all three circles intersect is where the epicenter is located.

To find an epicenter you need three seismograph stations. Where are three radiui interest is where the epicenter is located.

7.2 Notes The Richter scale measures the magnitude. magnitude – the strength of an earthquake The Mercalli scale measures the intensity. intensity – the amount of damage caused by an earthquake

How do we measure an earthquake’s intensity – the amount of damage caused by an earthquake? 1. Magnitude – how strong it is (measured by the Richter scale) 2. Population – the more people are around when it happens the more dangerous it is 3. How much money it costs to repair the damages – the more money it costs the more damage was done 4. Location – Where did it happen?

How does the magnitude compare to the other factors that measure the intensity? YearEarthquake Location MagnitudeLocation setting Cost to rebuild Number of deaths 1970San Fernando 6.6Los Angeles Area $510 million Northridge 6.7Los Angeles Area $40 billion San Simeon 6.5Small town $250 million 2

7.3 tsunami – a giant ocean wave that forms after a volcanic eruption, an earthquake in the ocean, a landslide, or a big asteroid hitting the ocean. What is the major problem with a tsunami? Coastal flooding. Homes are destroyed due to the water damage.