EARTHQUAKES When good rock goes bad!

EARTHQUAKES Shaking of the ground caused by sudden release of energy stored in rocks.

STRESS! A force that acts upon a rock to change its shape or volume

Compression - pushing together Stress Types Add compression…

Tension - pulling apart Stress Types Add tension…

Shearing – pushing in opposite directions Stress Types Add shearing…

Fault Terminology

Types of Faults Normal Fault – results from tensional stress, hanging wall moves down relative to foot wall

Types of Faults Reverse Fault – results from compressional stress, hanging wall moves up relative to foot wall

Types of Faults Strike-Slip Fault – results from shearing stress, rocks on either side of fault slip past each other sideways with little motion up or down

Offset produced by 1906 San Francisco quake

When you finish your “It’s My Fault” lab activity, staple and turn in your completed lab and work on your vocabulary. The last question of each section is basically asking how will the river change, and how will the landscape be altered as a result of that change.

Fault review Associated with divergent boundaries; motion is tensional; hanging wall drops down relative to foot wall Associated with convergent boundaries; motion is compressional; hanging wall moves up relative to foot wall Associated with transform boundaries; motion is lateral; hanging wall moves right or left relative to foot wall; no up or down motion of foot wall/hanging wall

Focus and Epicenter

Types of seismic waves: Primary Waves (P-Waves) Secondary Waves (S-Waves) Surface Waves (Love and Rayleigh)

Primary Waves (P-Waves) The fastest wave, they arrive 1st Compressional motion in the wave (push-pull) Vibration is parallel to the direction of wave propagation

Shear waves (side-side) Vibration is perpendicular to the direction of wave propagation Secondary Waves (S-Waves)

Slowest and most destructive – Rayleigh Waves: elliptical motion – Love Waves: horizontal motion (perpendicular to travel) Surface Waves

Seismographs How are earthquakes detected?

Seismograph A sensitive instrument that detects earth movements. Seismogram Produced by a recording seismograph, a seismogram is a graphical record of the movement of the earth over time.

Reading a Seismogram

Calculating lag time (oh no, more math!) 7:14.27:17.4 To calculate lag time, simply subtract arrival time of S-wave from arrival time of P-wave. P-wave arrival time S-wave arrival time S - P = 7:17.4 – 7:14.2 = 3.2 minutes

3:004:005:006:007:008:009:0010:0011:0012:0013:0014:0015:00 1:002:003:004:005:006:007:008:009:0010:0011:0012:0013:00 9:0010:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:00

5:006:007:008:009:00 P wave arrival = S wave arrival = L wave arrival = Lag time =

Finding the Epicenter

Finding the Epicenter of an Earthquake – Extra Credit Use class code “ ” Follow the directions, do the activity, complete the quiz, and print out your certificate of completion. I’ll verify your score and put in 10 extra test points. Start with the “Demonstration” and “Travel Time” links, and then go to “Epicenter & Magnitude”. There are also a couple of tutorials available for extra help. Certificate due Monday, April 27th

How damage occurs in an earthquake SHAKING some areas shake more than others unconsolidated sediments landfill wetlands LIQUIFACTION water rises to Surface of sediments

August 31, 1886 Charleston, SC

~ magnitude over 60 people died felt from NEW YORK to CUBA; from BERMUDA to MISSISSIPPI RIVER Wooden houses did better than brick - why? Damage greatest on ‘made ground’ - why? Sand/mud volcanoes common; some fissures Charleston, SC August 31, 1886

Fissures

Offset Rail Road Tracks

Broad Street

East Bay Street

College of Charleston

Destruction was random

Need to know: ~ Wegener’s Theory – what started him thinking, what clues and evidence did he have? ~ The theory Harry Hess put forth – What did he find? What other evidence added to the idea that the seafloor was spreading? ~ The 4 basic layers of the Earth – physical nature of each (e.g. outer core is liquid, etc.) ~ Features associated with plate tectonics (Boundary types and related features such as trenches, ridges, etc.) ~ What drives plate motion ~ What causes earthquakes and where they occur (do not need to know seismic wave types, fault types or stress types for this test) ~ Review Chapters 5 & 6 (pp ) STUDY!

S – P = approx. 6 minutes Find that lag time difference between the S & P arrival time from seismic velocity graph, then come straight down to find the distance that station was to the earthquake Approximately 6 minutes

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