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Earthquakes & Earth’s Interior

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Presentation on theme: "Earthquakes & Earth’s Interior"— Presentation transcript:

1 Earthquakes & Earth’s Interior
Chapter 8 pg 217

2 Introduction to Earthquakes

3 Fun Facts Strongest Earthquake fingernail growth)
Valdivia, Chile fingernail growth) Magnitude 9.5 Florida and South Dakota least likely to have earthquakes Deaths 1,655 May 22, 1960 Largest Earthquake – America Ave. duration 30 seconds (California) 9.2 Longest earthquake Alaska 8 – 10 minutes March 28, 1964 9.1 – 9.3 magnitude Annual Occurrence “Great Sumatra-Andaman Earthquake” Magnitude /year Seahawks – 2013 7-7.9 – 15/year San Andreas Fault moves 2 in/yr (same as 137.6 db 1-2 on Richter Scale

4 Bill Nye on Earthquakes

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

6 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

7 e. Epicenter – place on surface directly above focus

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

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10 Imperial fault - displacement

11 2. Cause of Earthquakes (Elastic rebound hypothesis) a
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)

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

13 Elastic Rebound Page 220 figure 4

14 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

15 h. Foreshocks – small quakes before large earthquake i
h. Foreshocks – small quakes before large earthquake i. Fault segments behave differently 1) Fault creep – slow gradual movements 2) Regular slippage – small quakes 3) Stay locked for extended periods of time Fault creep – happens in a rather smooth manner Regular slippage – causes small quakes Locked faults – cause buildup of elastic energy for larger earthquakes

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17 B. Measuring Earthquakes
Intro Seismology – study of earthquake waves Seismographs – record earthquake waves Seismogram – recorded ground motion

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19 Seismographs Then Now

20 2. Earthquake waves a. Spread out in all directions b
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

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

22 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

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24 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

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

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

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30 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

31 4. Measuring Earthquakes a
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

32 Richter Scale and Magnitude

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

34 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

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

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

37 Factors Intensity Duration Material used in buildings Building design

38 Wood and steel frames = more flexible
Concrete needs to be reinforced

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

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

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

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

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

45 4. Predicting Earthquakes a
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

46 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

47 Nova – World’s Deadliest Earthquakes

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

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

50 2. Layers by composition a
2. Layers by composition a. Crust 1) Oceanic a) 7 km (4mi) b) Igneous rocks (basalt) c) Younger than continental rocks d) Ave. density 3.0 g/cm3

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

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53 b. Mantle 1) Middle layer 2) 1795 miles 3) Density 3. 4g/cm3 c
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

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

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56 c. Lower mantle 1) More rigid but still can flow 2) Bottom part is much more fluid from heat from core d. Outer core 1) Liquid 2) Flowing causes magnetic field e. Inner core – solid from pressure

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

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60 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

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63 S waves don’t go through core

64 E. Earthquake Safety Before Go over safety until it is instinctive
Teach everyone Have emergency supplies Battery radio Batteries First aid kit Water and food for 2 weeks Blankets

65 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)

66 e. Locate main turn-offs (water, gas, and electric) 2. During a
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

67 c. If cooking – turn off stove and take cover d
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

68 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

69 3. After a. Check for injuries b
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

70 The New Madrid Fault


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