Earthquakes & Earth’s Interior Chapter 8 pg 217

Bill Nye on Earthquakes 

A. What is an Earthquake? 1. Earthquakes a. A vibration of Earth produced by rapid release of energy within the lithosphere b. Happen along a fault c. Fault – fracture in the crust where movement occurs

d. Focus 1) Place where earthquake starts 2) Along a fault beneath surface 3) Energy goes out in all directions 4) Energy travels as seismic waves

e. Epicenter – place on surface directly above focus

f. Faults and change to earth’s surface 1) Vertical movement a) Known as uplifting b) Fault scarp – sharp edge ridge 2) Horizontal - displacement

Imperial fault - displacement

2. Cause of Earthquakes (Elastic rebound hypothesis) a. Convection currents move plates on both sides of fault b. Rocks bend and store elastic energy c. Resistance from friction is overcome d. Rocks slip at weakest point (fault)

e. Causes forces farther up fault resulting in more slippage f. Continues until energy is released and rock returns to previous state

Elastic Rebound Page 220 figure 4

g. Aftershocks 1) Smaller than original quake 2) Happen after original quake 3) Caused from additional movements along the fault 4) Cause damage to previously weakened buildings

Effects of initial earthquake

h. Foreshocks – small quakes before large earthquake i. Fault segments behave differently 1) Fault creep – slow gradual movements 2) Regular slippage 3) Stay locked for extended periods of time

B. Measuring Earthquakes 1. Intro a. Seismology – study of earthquake waves b. Seismographs – record earthquake waves c. Seismogram – recorded ground motion

Seismographs ThenNow

2. Earthquake waves a. Spread out in all directions b. Surface waves 1) Travel along earth’s outer layer 2) Up/down & side/side motion 3) Most destructive waves

4) Change volume of material temporarily by pushing/pulling 5) Slowest waves 6) Recorded by seismogram

c. Body waves 1) Travel through earth’s interior 2) P waves a) Push-pull waves (compress/expand) b) Push/pull rocks in direction wave travels c) Known as compression waves d) Fastest waves

3) S waves a) Shake particles at right angles to their direction of travel b) Transverse waves c) Change shape of material they pass through temporarily d) Gases and liquids will not transmit them b/c there is no elastic rebound to original shape

3. Locating an Earthquake a. Earthquake distance 1) Find time b/w 1 st P wave and 1 st S wave 2) Use a travel-time graph

b. Earthquake Direction 1) Need 3 seismic stations 2) Circles are distance of epicenter 3) Intersecting circles shows epicenter

c. Earthquake zones 1) Circum-Pacific belt a) Ring of fire b) Outer edge of Pacific Ocean c) 75% of world’s earthquake activity d) Philippines, Japan, Chile, Alaska 2) Mediterranean-Asian belt 3) Oceanic ridge system

4. Measuring Earthquakes a. Intensity – measures shaking based on amount of damage b. Magnitude – measures seismic waves c. Richter Scale 1) Based on amplitude of largest seismic wave 2) Logarithmic scale

Richter Scale and Magnitude

3) Only useful within 310 miles of epicenter 4) Scientists no longer use it, but the news does

d. Moment Magnitude 1) More accurate than Richter scale 2) Based on amount of displacement along fault 3) Only scale that estimates energy released by earthquakes

4) Calculating: a) Average amount of movement along fault b) Area of surface break c) Strength of broken rock

C. Destruction from Earthquakes Why does one building have almost no damage to it?

1. Factors a. Intensity b. Duration c. Material used in buildings d. Building design

1) Wood and steel frames = more flexible 2) Concrete needs to be reinforced

e. Liquefaction 1) Happens to loosely packed saturated soils 2) Soil turns into a liquid 3) Buildings settle, underground structures rise

2. Tsunamis a. Causes 1) Ocean floor is displaced vertically 2) Underwater landslide

b. Characteristics 1) Move quickly in open ocean 2) Can go unnoticed 3) Waves slow and increase in size as depth decreases

c. Warning system 1) Use water levels in tidal gauges 2) Provides about 1 hour warning Importance

3. Other dangers a. Landslides 1) Most damage 2) Landslides, slopes fail, ground collapses, gas and water lines break b. Fire

4. Predicting Earthquakes a. Short-range 1) Study uplift, strain in rocks, water levels, pressure in wells, radon gas emission, electromagnetic properties in rocks 2) Hasn’t been successful

b. Long-range 1) Probability of certain magnitude earthquakes happening w/in yrs 2) Important for building codes 3) Based on that earthquakes are cyclical 4) Study seismic gap – no activity for long periods of time 5) Limited success

D. Earth’s Layered Structure 1. Intro a. We have only drilled 7.5 miles b. How do we know what the inside looks like? - Studying earthquake waves

c. Waves speed up with depth b/c of pressure d. Pressure causes waves to refract

2. Layers by composition a. Crust 1) Oceanic a) 7 km (4mi) b) Igneous rocks (basalt) c) Younger than continentalrocks d) Ave. density 3.0 g/cm 3

2) Continental a) 8 – 75 km (5-47mi) b) Average 40 km c) Older than oceanic crust

b. Mantle 1) Middle layer 2) 1795 miles 3) Density 3.4g/cm3 c. Core 1) Iron-nickel alloy 2) Density 13 g/cm3 3) 2162 miles

3. Layers by physical properties 1) Lithosphere a) Rigid shell b) Crust and upper mantle 2) Asthenosphere a) Upper mantle b) Rocks near melting point c) Putty like substance

3) Lower mantle a) More rigid but still can flow b) Bottom part is much more fluid from heat from core 4) Outer core a) Liquid b) Flowing causes magnetic field 5) Inner core – solid from pressure

4. Discovering layers a. Finding crust/mantle 1) Moho discontinuity – place where seismic waves speed up 2) Named after Andrija Mohorovicic

b. Finding outer core (fig 16 pg 236) 1) P waves bend around liquid core 2) Shadow zone – p waves arrive minutes slower than expected through outer core 3) S waves can’t go through liquid

S waves don’t go through core

E. Earthquake Safety 1. Before a. Go over safety until it is instinctive b. Teach everyone c. Have emergency supplies 1) Battery radio 2) Batteries 3) First aid kit 4) Water and food for 2 weeks 5) Blankets

d. Arrange home for safety 1) Heavy things on bottom shelf 2) Breakables with latched doors 3) Don’t hang heavy things (mirrors, pictures, etc.) above where people sleep 4) Anchor heavy appliances 5) Flammable liquids away from ignition sources (water heaters, stoves, furnaces)

e. Locate main turn-offs (water, gas, and electric) 2. During a. Stay inside b. Move: 1) Under desk or table 2) Interior wall 3) NOT by windows, mirrors, fireplaces, and hanging objects

c. If cooking – turn off stove and take cover d. If outside 1) Move to open area 2) Get away from buildings, power lines, and trees

e. If driving 1) Stop on side of road 2) Don’t stop under bridges and overpasses, power lines, trees, large signs 3) Stay in car

3. After a. Check for injuries b. Check for damage to see if you are safe c. Smell gas – open windows and get outside d. Smell/see frayed wires – turn off electric and get outside

The New Madrid Fault 