Earthquakes Oct 11, 2010

Objectives I will be able to describe an earthquake’s features such as epicenter, focus, magnitude, and intensity I will be able to analyze the energies of seismic earthquake waves I will be able to determine earthquake location from a travel-time graph

Key Points To describe the location of earthquakes, we use the terms focus and epicenter When analyzing how earthquakes travel, we talk about the 3 main types of earthquake waves: s, p, and surface – These waves travel at different speeds and cause differing amounts of destruction – The magnitude of an earthquake measures the amplitude of the largest wave Major earthquakes can be preceded by foreshocks and followed by aftershocks The intensity of an earthquake describes the amount of shaking at a specific location

What are Earthquakes? Earthquake video Take note of at least 4 facts 1.______________________ 2.______________________ 3.______________________ 4.______________________

Cause of Earthquakes What causes earthquakes to occur? Where do we usually find earthquakes occurring?

Cause of Earthquakes Earthquakes are the vibration or shaking of the Earth produced by the rapid release of energy When rocks are subjected to large forces, such as those associated with plate movement, the rocks are stressed and strained When rocks cannot withstand the stress any longer, they break or shift and energy is released Faults are fractures in the earth where movement has occurred Energy release  Vibrations  Earthquakes

Earthquake features 1. Location – Focus: the place where the earthquake starts- the source Energy radiates out in all directions – Epicenter: the location on the surface of earth directly above the focus

Earthquake features 2. Foreshocks: smaller earthquakes that precede or come before major earthquakes 3. Aftershocks: smaller earthquakes that occur after major earthquakes 4. Intensity: the amount of shaking produced by an earthquake at a given location 5. Magnitude: the “size” of the earthquake - Richter magnitude: determined from the amplitude (height) of the largest seismic wave - Moment magnitude: determined from the displacement (movement) of the fault zone

Earthquake Waves All of the above features are a result of the earthquake waves that transport the energy from the focus outward in all directions Two general categories – Surface waves: travel along Earth’s surface – Body waves: travel from the focus through Earth’s layers

Earthquake Waves Surface waves – Travel along Earth’s outer layer – Their motion is complex Like waves move a ship on the ocean Up/down and side-to-side motion – The most destructive type of earthquake wave Because they travel along the ground they cause anything resting on the land to move

Earthquake Waves Body waves- 2 types 1. P-waves Primary waves- they arrive first Travel the fastest Classified as “compressional waves”- push-pull motion Can travel through solids, liquids, and gases

Earthquake Waves Body waves 2. S-waves Secondary/seismic waves- they arrive after P-waves Travel more slowly than P-waves Travel at right angles to the direction they move Travel through solids only

Check In – Answer the following on a SEPARATE piece of paper in COMPLETE sentences: 1.What is the epicenter of an earthquake? 2.What is the source of an earthquake called? 3.What are the smaller earthquakes that precede major earthquakes called? 4.Which type of seismic wave travels the fastest? 5.Which type of seismic wave travels the slowest? 6.Which type of seismic wave causes the most destruction? 7.What is the amount of shaking produced by an earthquake at a given location?

Locating Earthquakes- Part I Because P-waves and S-waves travel at different speeds we can use the difference in their arrival times at a given location to figure out the distance to the earthquake’s epicenter This information is presented in a travel-time graph

Reading Travel-time graphs A. Time in minutes for the arrival of the waves B. Distance from the recording station to the epicenter - kilometers at the top - miles at the bottom

To find when a wave will be received when given the distance between the seismic station and epicenter… 1. Find the distance along the x-axis ** make sure you are using the correct units ** look at the top and bottom 2. Follow the distance line up to where it meets the S-wave or P-wave curve. 3. Go across to the y-axis to find the time

When will the first P wave be received if an earthquake epicenter is approximately 3000 kilometers from the seismic station? _____________ _____________

To find the distance between the seismic station and epicenter given the arrival time of one wave… 1. Find the arrival time along the y-axis. 2. Follow that time across until you hit the wave curve line. 3. Go down/up to the distance – make sure you check your distance units!

If the first S wave arrives after 9 minutes, what is the distance between the epicenter and seismic station? ____________

To find the distance between the seismic station and epicenter given the difference in arrival times between s-waves and p-waves… 1. Look at the S-wave curve and P-wave curve to find where they are separated by the amount of time given. 2. Follow that line down/up to the distance in the appropriate units Ex: difference in p wave and s wave arrival time is 5 min. How far is the seismic station from the epicenter in miles?

What would the difference in travel times between the first P-wave and first S-wave be if the seismic station is 1500 miles from the epicenter? ____________

To find the difference in wave arrival time given the distance between the seismic station and epicenter… 1. Find the distance along the x-axis 2. Follow the distance line up to the P-wave and S-wave curves. 3. Using the times on the y-axis, calculate the difference in arrival times of the two waves

What would the difference in travel times between the first P-wave and first S-wave be if the seismic station is 4000 km from the epicenter? ____________

Warm-Up 10/13/10 The Richter magnitude of an earthquake is determined from the ___. A.Duration of an earthquake B.Intensity of an earthquake C.Arrival times of P waves and S waves D.Measurement of the amplitude of the largest seismic wave What is the epicenter of an earthquake? Which seismic waves travel the most rapidly? Which are the most destructive? O

Objectives Today I will be able to: – Analyze the number of seismic stations necessary to locate an earthquake epicenter – Describe other natural side effects of earthquakes – Analyze how earthquake waves provide information about earth’s interior – Describe earthquake safety measures

Locating Earthquakes- Part II Using earthquake waves to locate an epicenter ESSENTIAL QUESTION WHILE YOU’RE WATCHING… HOW MANY SEISMIC STATIONS WOULD YOU NEED TO ACCURATELY LOCATE AN EARTHQUAKE EPICENTER? _____________

Other useful information from earthquake waves Earthquake waves tell us the location of an earthquake’s epicenter and focus Earthquake waves also tell us about the make up of the Earth’s interior – This information is available because s- waves and p-waves travel at different speeds and are able to pass through different materials

Effects of Earthquakes Main effect of earthquakes… A lot of destruction Side effects: – Tsunamis- “seismic sea waves” triggered by earthquakes occurring underwater Ocean waves caused by submarine earthquakes – Landslides- ground movement and liquefaction – Fires- broken gas lines and electrical wires

Effects of Earthquakes San Francisco Earthquake 1989 Look at how widespread the effects of the Earthquake are!

Effects of Earthquakes Where did you see the earthquake affecting people? At some of these locations and other locations in the area, people were seriously injured… At other location people were alright. Watch this next clip to figure out why Destruction in California Earthquake

Earthquake Safety Structures that withstood the shaking… – Candlestick park Built on reinforced bedrock Structures that did not withstand the shaking… – Bay Bridge- too stiff and not well reinforced – Freeway in Oakland- not flexible or reinforced – Landfill Soft land Buildings sank and collapsed, water and gas lines broke

Earthquake Safety Buildings can sink!? – The process is known as liquefaction – Let’s see how it works – Liquefaction Liquefaction Bottom line: The safest location during a major earthquake would be an area with solid bedrock… and if possible a location that has been reinforced

Recent Earthquakes Listen as I describe and we watch footage from recent earthquakes in Haiti and Chile. Both suffered devastating Earthquakes this year, while you watch thing of things they have in common and things that are different about them. – n_haiti.html n_haiti.html – n_chile.html n_chile.html

Venn Diagram 1.On a half sheet of paper, create a Venn Diagram comparing the earthquakes. – 4 things only about haiti – 4 things only about chile – 4 things in common 2.WRITE A PARAGRAPH (5-8 sentences long) describing the earthquakes and their destruction using key terms from yesterday and today IN YOUR OWN WORDS on the back of the diagram.