Chapter 19 - Earthquakes 19.1- Forces within Earth

1/5/16, Tuesday To-Do Bellringer: What causes Earthquakes? Get a copy of the Learning Target Inventory off of the front stool. Rate yourself on each learning target. If you have not taken your semester 1 exam yet, I’ll be giving it to you tomorrow.

1/5/16 Tuesday Often, you may hear people say that the animals and fish seemed to sense there is an earthquake coming. Why/how do you think that may be possible?

To-Do 1/4/16, Monday Bellringer: What would you do during an earthquake?

Bellringer: 1/6/16 Wednesday *Define what you think Stress and Strain is as they apply to rocks. Get a copy of the guided notes off of the front stool. We’ll Finish reviewing earthquake safety and take notes on stress and strain.

Earthquakes: Earthquake = vibrations caused by movement in crust Are the result of movement of crust produced by Plate tectonics Stress = total force acting on crustal rocks Builds up overtime Overcomes strength of rocks and causes movement along fractures in rock

http://earthquake.usgs.gov/learning/kids/sciencefair.php Stress Three types Compression – decrease volume of material Tension – pulls material apart Shear – causes material to twist Strain = deformation of material in a response to stress

Deformation Elastic – when a material is compressed, bent, or stretched at low stress Material can return to “normal” when stress is zero Example: Pulling on a rubber band

Deformation Plastic – stress builds up past elastic limit Permanent deformation – stays changed even when stress is zero Point of Rupture = failure Example: Pulling rubber band until it breaks

Deformation Most materials exhibit varying degrees of plastic and elastic deformation http://www.uwsp.edu/geo/faculty/ritter/images/lithosphere/Earth_Structure/plastic_deformation.jpg

Bellringer: Compare and contrast the movements of each of the three types of faults. Page 531 in your book.

Faults notes: Any fracture or system of fractures along which Earth moves Happens along weak regions Fault plane = surface along which movement takes place

Fault Animation: Fault Motion: http://www.iris.edu/gifs/animations/faults.htm Examine animations of fault motion: http://www.classzone.com/books/earth_science/terc/content/visualizations/es1103/es1103page01.cfm

What kind of fault is it?

Fence offset produced by 1906 San Francisco earthquake Right-Lateral Strike-Slip Faults The fence was offset 2.6 m by the magnitude 8.2 earthquake of April 18, 1906, San Francisco, California. The section of the San Andreas fault shown here is 0.8 km north of Woodville. The photo is looking northeast. The lateral or strike-slip fault offset is large; however, the trace is nearly invisible. This earthquake, together with the fire that followed, resulted in more than 3,000 deaths and 400 million dollars of property damage. [Photo credit: G.K. Gilbert, U.S. Geological Survey. Photo has been colorized.] 

What kind of fault is it?

The footwall is on the left The footwall is on the left. Since the beds indicate that the hanging wall has risen relative to the footwall, this is a reverse fault.

What kind of fault is it?

If you stood on the fault plane, the block on the right would be under your feet. This is thus the footwall. The red line marks equivalent layers on opposite side of the fault. Since the hanging wall dropped relative to the footwall, this is clearly a normal fault.

http://facweb.bhc.edu/academics/science/harwoodr/Geol101/study/Images/ReverseFault.gif Faults Reverse Fault – form as a results of horizontal and vertical compression that squeezes rock Seen near convergent plate boundaries Two areas end up closer together after faulting

Faults Normal fault – movement partly horizontal and partly vertical http://facweb.bhc.edu/academics/science/harwoodr/Geol101/study/Images/NormalFault.gif Faults Normal fault – movement partly horizontal and partly vertical Horizontal movement pulls rocks apart and stretches crust Vertical movement causes one side of rock to move down relative to the other side Two areas end up farther apart after faulting

Faults Strike-slip fault – caused by horizontal shear http://facweb.bhc.edu/academics/science/harwoodr/GEOL101/Study/Images/StrikeSlipRLFault.gif Faults Strike-slip fault – caused by horizontal shear Movement is mainly horizontal in opposite direction Example: San Andreas Fault Creates offset features after movement

Discuss: Evaluate how earthquake intensity is related to the type of fault.

Bellringer: Contrast the three types of seismic waves.

Earthquake waves Seismic waves = vibration of the ground produced during an earthquake Primary waves = squeeze and push rocks in same direction wave is traveling Secondary waves = cause rocks to move at right angles relative to wave direction Slower than P waves Surface waves = cause most destruction and take longest to past Slowest wave, only travel of Earth’s surface

Seismic Waves http://www.seismo.unr.edu/ftp/pub/louie/class/100/waves.GIF

Earthquake Focus = point where waves originate Epicenter = point on surface directly above focus http://stevekluge.com/geoscience/images/epicenter.jpg

In-Class Assignment/Homework