Ch 19 Earthquakes Shake, Rattle, and Roll!

Lesson 7 Forces and Faults

Think About It… What happens to a rubber band that is stretched past its elastic limit?

Focus Question… What causes earthquakes?

A. Stress and Strain… What are earthquakes? natural vibrations of the ground caused by movement along gigantic fractures in Earth’s crust

Stress and Strain… 1. When do most earthquakes occur? when rocks fracture (break) deep within Earth 2. When do fractures form? when stress exceeds the strength of the rocks involved

Stress and Strain… 3. What is stress? … the forces per unit area acting on a material … There are three types of stress.

Stress Compression decreases the volume of a material – occurs at convergent boundaries

Stress! Tension pulls a material apart – at divergent boundaries

Stress! Shear (horizontal) causes a material to twist – at transform boundaries.

Strain! 5. What is strain? the deformation of materials in response to stress It is represented by the solid line on your diagrams.

Elastic Limit 6. A slab of rock’s elastic limit is… … the point at which it will undergo permanent deformation 7. Failure is… … when a material breaks! We call this failure an earthquake!

Faults… 1.Rocks will fail and form a fault…when stress is applied too quickly or when stress is great 2.A fault is the resulting fracture (or system of fractures) along which movement occurs.

Reverse Fault…  Is caused by… compression (at a convergent boundary)  Movement of crust… block above fault moves up and over ations/faults.htm

Reverse Fault – The Himalayas!

Normal Fault…  Is caused by… tension (at a divergent boundary)  Movement of crust… block above fault moves down

Normal Fault – The Sierra Nevadas

Strike-slip Fault…  Is caused by… horizontal shear (at a transform boundary)  Movement of crust… blocks slide past each other horizontal (no vertical movement)

The San Andreas Fault… 

Lesson 8 Seismic Waves and Earth’s Interior

Think About It… Is it possible to go to Earth’s core?

Focus Question… What are seismic waves and what can we learn from a travel-time graph?

The Focus of an Earthquake… 1.The focus of an earthquake is where the rocks break at least several miles beneath Earth’s surface. 2.The epicenter is the location on Earth’s surface just above the focus Draw the picture.

The Focus of an Earthquake…

Earthquake Waves… 1. What are seismic waves? vibrations of the ground during an earthquake Seismic Wave Rap! be.com/watch?v= x1tb6HwyaHg

Earthquake Waves… 2. How do the following types of seismic waves move rocks? a. Primary (P) waves – squeeze (push) & pull rocks in the same direction as the wave

Earthquake Waves… 2. How do the following types of seismic waves move rocks? b. Secondary (S) waves – cause rocks to move at right angles to direction of the wave

Earthquake Waves… c. Surface waves – move in 2 directions – up and down and side to side (slowest and most damaging!)

Seismic Waves and a Seismogram…  “So which wiggles are the earthquake? The P wave will be the first wiggle that is bigger than the rest of the little ones (the microseisms). Because P waves are the fastest seismic waves, they will usually be the first ones that your seismograph records. The next set of seismic waves on your seismogram will be the S waves. These are usually bigger than the P waves. The surface waves are the other, often larger, waves marked on the seismogram. Surface waves travel a little slower than S waves (which, in turn, are slower than P waves) so they tend to arrive at the seismograph just after the S waves.”

Seismogram (Add to notes) warning.com/pages/seismo graph#.VFpac3JdVps

Travel-Time Graph (not time travel!) 1. A travel-time graph is … shows average travel time of P & S waves 2. This graph is used to calculate… the distance to the epicenter (using the difference in arrival times of the p and s waves)

Travel-Time Curves (p. 501) Suppose the waves recorded on a seismogram at Station A are farther apart than they are at Station B… The epicenter is farther from Station A. Animation for Lab 8 on next slide 

Lab Lesson 8 Animation of Waves… ray.org/Labs/SeismicWaves/

Lesson 9 Measuring and Locating Earthquakes

Think About It… What is the strongest earthquake that has happened in your lifetime?

Focus Question… How are earthquakes measured and located?

Earthquake Magnitude and Intensity How is the amount of energy released by an earthquake measured? by its magnitude Haiti, 1/2010 (7)

The Richter Scale… a. The Richter scale is based on… size of the largest seismic waves generated by the quake (EQ) b. Each successive number on this scale represents… a 10 times increase in wave size c. Each increase in magnitude corresponds to… A 32-times increase in seismic energy d. A magnitude 8 EQ releases 32 times more energy than a magnitude 7 EQ.

The Richter Scale Haiti, 1/2010 (7) Japan, 3/2011 (9)

The Modified Mercalli Scale… a. The intensity of an earthquake can be determined by… amount of damage done to the structures involved (intensity) b. The modified Mercalli scale is used to determine the intensity of an EQ by… rate damage & other effects as noted by observers This scale uses Roman numerals from I to XII. It was developed by Giuseppe Mercalli in

Modified Mercalli Scale… Did you feel it? usgs.gov sgs.gov/earthquake s/eventpage/dyfi/?e nabled=false

Measuring Earthquakes: The Basics  SRtxA SRtxA

Modified Mercalli Scale… d. A seismic intensity map is made by… … compile the MMsI values (Modified Mercalli scale intensity values), plot them on a map, & join points of similar intensity. (See map on back.) Mercalli values at distances very far from the epicenter… Decrease to I

Seismic Intensity Map… Northridge, California Earthquake

Damage in Northridge, Ca…

More Damage in Northridge, Ca…

Depth of Focus… e. Another factor that determines the intensity of an earthquake is … The depth of an EQ’s focus Shallow-focus events will produce catastrophic quakes with high intensity values.

Locating an Earthquake… 1. The distance to an earthquake’s epicenter is determined by… the time difference b/tw the arrival of the P-wave & the S-wave 2. This distance is called… Epicentral distance 3. Three seismograph stations are needed to determine an EQ’s epicenter.

Locating an Earthquake…  5. A travel-time graph determines the exact time of an EQ. 3. Three seismograph stations are needed to determine an EQ’s epicenter.

Seismic Belts… p Most earthquakes are associated with… Tectonic plate boundaries 2. 80% of earthquakes occur in… The Circum-Pacific Belt 3. Another 15% of earthquakes occur at the Mediterranean-Asian Belt 4. Most of the remaining earthquakes occur at mid-ocean ridges

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Reinforcement 9…

Lab 9 USA Map…

Lesson 10 Earthquake Hazards

Think About It… Why do developing countries such as Haiti suffer such devastation from earthquakes?

Focus Question… How do earthquakes affect the four spheres of Earth?

Structural Failure… 1. The types of buildings that sustain the most severe damage from earthquakes are… Unreinforced, made of stone, concrete, or other brittle materials Typical building in Iraq Church, Armenia, 1988

Unreinforced Masonry Building: A Mission in California

Structural Failure… 2. The types of buildings that sustain the least amount of damage from earthquakes are… wooden high-rise, steel-framed Kobe, Japan 1995

Structural Failure… 3. Pancaking is… supporting walls of ground floor collapse causing upper floors to collapse Pancaked Building in Turkey

Structural Failure… 4. Building with stories may collapse because… their natural sway has the same vibration period of an EQ

Preventing Structural Failure, Golden Gate Bridge, CA

Land and Soil Failure… 5. Earthquakes in sloping areas can trigger… landslides! El Salvador, 2001, mag 7.6

Land and Soil Failure 6. Soil liquefaction subsurface materials liquefy & behave like quicksand due to EQ vibrations s/animation.php?flash_title=Liquefacti on&flash_file=liquefaction&flash_width =450&flash_height=200

Animation of Liquefaction…

Land and Soil Failure… 7. T here was much damage to structures in the Mexico City EQ of 1985 b/c... It is built on soft sediments.

Fault Scarps… 8. A fault scarp is… area of great vertical offset where the fault intersects Earth’s surface. 9. The fault scarp shown created a… waterfall

Tsunamis… 10. A tsunami is caused by… vertical motion of seafloor (during the EQ) bumps the water over the fault 11. A tsunami in the open ocean is usually… 1 meter high (3 ft) You wouldn’t notice it if you were there! Tsunami strikes Ao Nang, ThailandAo Nang

Tsunamis… 12. A tsunami is dangerous when it enters shallow water because… it moves very fast it can be very high – up to 30m (90 ft)! Sri Lanka, 2004

Tsunamis… 13. The most recent devastating tsunami was in… Japan, March 2011 Youtube Clip: e.com/watch?v=V2t aJExhV6g e.com/watch?v=V2t aJExhV6g

5H9oEQ One and a half minute clip of a tsunami drill in Oregon.

Tsunami Warning Sign in Monterey, CA

Tsunami Evacuation, Washington State

Warning Sign in Astoria, Oregon!

Seismic Risk… 14a. Five states with the greatest seismic risk… Alaska California Hawaii Utah Nevada b. The San Andreas Fault is a transform boundary.

Seismic Risk… 14c. The seismic risk of the NC Piedmont and mountains… moderate 14d. The seismic risk of the coastal plains of NC… low

Seismic Risk in the USA

Earthquake Prediction… 15. Earthquake recurrence rates indicate … Where EQs happen (occur) repeatedly (at regular intervals to generate similar quakes)

Earthquake Prediction… 16. Seismic gaps are sections of active faults that haven’t had big EQs for a while An earthquake is likely to happen here! The San Andreas Fault

Earthquake Prediction… 17. Why is earthquake prediction important? … to save lives and prevent property damage!! San Andreas Fault

Extra Slides that discuss Earth’s Interior…

F. Clues to Earth’s Interior (p. 503) 1. Where does the knowledge of Earth’s interior come from? The study of seismic waves 2. How do P-waves and S-waves move through the mantle? They follow fairly direct paths 3. What do P-waves do when they strike the core? They bend 4. Why don’t S-waves enter Earth’s core? They cannot travel through liquids

Clues to Earth’s Interior 5. What does the disappearance of S- waves tell us about Earth’s outer core? That it must be liquid 6. What shows us that Earth’s inner core is solid? Studies of how P waves are deflected deep within Earth

G. Earth’s Internal Structure…  Crust of lithosphere – granite (continental crust), basalt (oceanic crust)  Upper mantle – peridotite (intrusive, bumpy, igneous)  Asthenosphere – peridotite  Lower mantle – oxides of iron, silicon, and magnesium  Core – iron and nickel (magnetic field is generated here!

G. Earth’s Internal Structure …