Earthquakes Shake, Rattle, and Roll!

Lesson 7 Forces and Faults

What causes earthquakes? Focus Question… What causes earthquakes? Where are they located?

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… … the forces per unit area acting on a material http://www.empireonline.com/images/features/100greatestcharacters/photos/25.jpg Stress and Strain… 3. What is stress? … the forces per unit area acting on a material … There are three types of stress…

Stress Compression (squeezed material) decreases the volume of a material – occurs at convergent boundaries (& reverse faults) http://rst.gsfc.nasa.gov/Sect2/05-01_reverse_fault-jyougashima_DSC8766.jpg

Stress! Tension (stretched material) pulls a material apart – at divergent boundaries (& normal faults)

http://rpmedia. ask. com/ts http://rpmedia.ask.com/ts?u=/wikipedia/commons/thumb/b/b1/Boudin_vein.jpg/180px-Boudin_vein.jpg Stress! Shear (twisted material)causes a material to twist – at transform boundaries (& strike-slip faults).

Strain! the deformation of materials in response to stress 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 material breaks! We call this failure and earthquake!

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

Reverse Fault… Is caused by… Movement of crust… compression Movement of crust… block above fault moves up and over convergent boundary http://www.iris.edu/gifs/animations/faults.htm http://homepage.ufp.pt/biblioteca/GlossarySaltTectonics/PlatesJPG/Fig.R018-ReverseFault.jpg

Reverse Fault – The Himalayas! http://www.geographicguide.net/earth/pictures/himalayas-asia.jpg http://img.wylio.com/flickr/500/494666903

Normal Fault… Is caused by… tension (at a divergent boundary) http://geology1a-1.wikispaces.com/file/view/NormalFault.gif/90969209/NormalFault.gif Normal Fault… Is caused by… tension (at a divergent boundary) Movement of crust… block above fault moves down Divergent boundary)

Normal Fault – The Sierra Nevadas http://fela2fela.files.wordpress.com/2012/02/sierra-nevadas.jpg http://www.pbs.org/weta/thewest/places/states/california/ca_sierra.jpg

Strike-slip Fault… Is caused by… horizontal shear Movement of crust… http://7bcore3.wikispaces.com/file/view/StrikeSlipLLFault%5B1%5D.gif/193098468/StrikeSlipLLFault%5B1%5D.gif Strike-slip Fault… Is caused by… horizontal shear Movement of crust… blocks slide past each other horizontal (no vertical movement) http://www.iris.edu/gifs/animations/faults.htm Transform boundary

The San Andreas Fault… http://www.sanandreasfault.org/

Draw and label these Faults Define “Fault” in your own words

Seismic Waves and Earth’s Interior Lesson 8 Seismic Waves and Earth’s Interior

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

The Focus of an Earthquake… The focus of an earthquake is where rocks break beneath (Earth’s) surface. The epicenter is the location on Earth’s surface just above the focus. http://www.em.gov.bc.ca/Mining/Geoscience/SurficialGeologyandHazards/Earthquakes/PublishingImages/eq-2b.gif

Depth of Focus… The depth of an EQ’s focus 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. (closer to the dynamite!)

Earthquake Waves… vibrations of the ground during an earthquake http://gomyclass.com/geology10/files/lecture9/html/web_data/file22.htm Earthquake Waves… 1. What are seismic waves? vibrations of the ground during an earthquake “seismo-” means shaking!

Earthquake Waves… 2. How do the following types of seismic waves move rocks? Primary (P) waves – squeeze (push) & pull rocks in the same direction as the wave http://www.youtube.com/watch?v=2rYjlVPU9U4 http://allshookup.org/quakes/wavetype.htm

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 http://www.youtube.com/watch?v=en4HptC0mQ4

Earthquake Waves… Seismic Wave Rap! c. Surface waves – move in 2 directions – up and down and side to side (slowest and most damaging!) Seismic Wave Rap! http://www.youtube.com/watch?v=x1tb6HwyaHg

Seismic Waves and a Seismogram… http://www.geo.mtu.edu/UPSeis/reading.html “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.”

Travel-Time Graph (not time travel!) 1. A travel-time graph is … shows average travel time of P & S waves This graph is used to calculate… the distance to the epicenter (using the difference in arrival times of the p and s waves) http://mtweb.mtsu.edu/cribb/100eq.html

Travel-Time Curves 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 

F. Clues to Earth’s Interior 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 http://www.columbia.edu/~vjd1/ray_paths.gif

Measuring and Locating Earthquakes Lesson 9 Measuring and Locating Earthquakes

What is the strongest earthquake that has happened in your lifetime? Think About It… What is the strongest earthquake that has happened in your lifetime? When was the last earthquake in NC? Murphy NC

How are earthquakes measured and located? 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)

1. The Richter Scale… An 8 is 10 times bigger than a 7 The Richter scale is based on… size of the largest seismic waves generated by the quake (EQ) Each successive number on this scale represents… a 10 times increase in wave size An 8 is 10 times bigger than a 7 An 8 is 100 times bigger than a 6

1. The Richter Scale… Each increase in magnitude corresponds to… A 32-times increase in seismic energy An 8 releases 32 times more energy than a 7 An 9 releases 1024 times more energy than a 7 Bill Nye Richter scale

The Richter Scale Haiti, 1/2010 (7) Japan, 3/2011 (9) http://sahanasingh.wordpress.com/2011/05/17/failing-to-prepare/

2. The Modified Mercalli Scale… The intensity of an earthquake can be determined by… amount of damage done to the structures involved (intensity) 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 1902. http://www.geo.mtu.edu/UPSeis/intensity.html

Modified Mercalli Scale… Did you feel it? usgs.gov http://earthquake.usgs.gov/earthquakes/eventpage/dyfi/?enabled=false http://scearthquakes.cofc.edu/images/MercalRichtscale.gif

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

Seismic Intensity Map… Northridge, California Earthquake

Look at the text page Where do most earthquakes occur in California? Intensity Map of the Northridge Earthquake.

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

Locating an Earthquake… 3. Three seismograph stations are needed to determine an EQ’s epicenter. 5. A travel-time graph determines the exact time of an EQ. http://www.geo.mtu.edu/UPSeis/images/triangle.gif

Seismic Belts… 80% of earthquakes occur in… Most earthquakes are associated with… Tectonic plate boundaries 80% of earthquakes occur in… The Circum-Pacific Belt Another 15% of earthquakes occur at the Mediterranean-Asian Belt Most of the remaining earthquakes occur at mid-ocean ridges http://earthquake.usgs.gov/

Lesson 10 Earthquake Hazards

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

How do earthquakes affect the four spheres of Earth? Focus Question… How do earthquakes affect the four spheres of Earth? What are the 4 spheres again?

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 http://www.siampinoy.net/forum/55-ano-ba-ang-latest-post-it-here/88292-chile-earthquake-may-have-shortened-days-on-earth.html

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

Structural Failure… 4. Building with 5-15 stories may collapse because… their natural sway has the same vibration period of an EQ EQ Proof Building – Futures Channel http://www.wbdg.org/resources/seismic_design.php

Land and Soil Failure… landslides! 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 http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Liquefaction&flash_file=liquefaction&flash_width=450&flash_height=200 http://en.wikipedia.org/wiki/Soil_liquefaction

Land and Soil Failure… It is built on soft sediments. 7. Soft materials have no resistance to deformation. There was much damage to structures in the Mexico City EQ of 1985 b/c... It is built on soft sediments. http://seismo.berkeley.edu/blogs/seismoblog.php/2008/09/19/title

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

Tsunami strikes Ao Nang, Thailand 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! http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami

Tsunamis… Sri Lanka, 2004 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.)!

Tsunamis… 13. A recent devastating tsunami was in… Japan, March 2011 Youtube Clip: https://www.youtube.com/watch?v=V2taJExhV6g 13. A recent devastating tsunami was in… Japan, March 2011

Seismic Risk… 14a. Five states with the greatest seismic risk… Alaska California Hawaii Utah Nevada b. The San Andreas Fault is a transform boundary. http://pubs.usgs.gov/fs/2005/3052/images/map.jpg

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

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

Earthquake Prediction… http://upload.wikimedia.org/wikipedia/commons/8/8d/San_Andreas.jpg Earthquake Prediction… 16. Seismic gaps are sections of active faults that haven’t had 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!! http://www.youtube.com/watch?v=_YLjIvJXhpg San Andreas Fault

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!