1. EARTHQUAKES AND EARTH’S INTERIOR

2. Objectives
Explain the connection between earthquakes and plate tectonics.
Identify several earthquake-related hazards.
Define body waves and surface waves.
Explain how the materials in Earth’s interior affect seismic waves.
Define and describe the composition of Earth’s crust, mantle and core.

3. Megathrust earthquakes

4. Earthquakes and earthquake hazards
Seismology
The scientific study of earthquakes and seismic waves
Seismic waves
An elastic shock wave that travels outward in all directions from an earthquake’s source
Seismic creep

5. Earthquakes and plate motion
The elastic rebound theory
Continuing stress along a fault
Results in buildup of elastic energy in the rocks
Energy abruptly released when an earthquake occurs

6. Earthquakes and plate motion

7. Earthquake Hazards and Predictions
Primary hazards
Collapsing buildings, bridges and other structures
Aftershock
Secondary hazards
Landslides, fires, ground liquefaction, tsunamis

9. Earthquake hazards Landslide, Huascaran, Peru
Open fissure, Golcuk, Turkey

10. Earthquake hazards Fire, San Francisco, California
Ground liquification, Niigata, Japan

11. The Sumatra-Andaman Tsunami (2004)

12. Earthquake prediction
Short-term prediction and early warning
Precursor phenomena
Foreshocks
Long-term forecasting
Paleoseismology
The study of prehistoric earthquakes
Seismic gaps

14. Earthquake Readiness
Preparation and readiness to earthquakes key to reducing fatalities
Reinforced structures
Bolting wood-framed buildings to foundation
Protecting utility lines from movement
Education

15. The Science of Seismology
Seismograph
An instrument that detects and measures vibrations of Earth’s surface
Advanced seismographs detect vibrations 10-8 of a centimeter
Seismogram
The record made by a seismograph

16. The Science of Seismology

17. Seismic waves Body wave Surface wave Focus
Travels through Earth’s interior
Surface wave
Travels along Earth’s surface
Focus
Where rupture commences and an earthquake’s energy is first released

18. Locating earthquakes Compressional wave: Shear wave:
Wave consisting of alternating pulses of compression and expansion
Can pass through any medium (solids, liquids, gases)
P (or primary) wave
Shear wave:
Rock is subjected to side to side or up and down forces, perpendicular to wave’s direction of travel
S (secondary) wave
Not transmitted through water
Travel slower than P waves

19. Locating earthquakes

20. Locating earthquakes

21. Locating earthquakes Epicenter
The point on Earth’s surface directly above an earthquake’s focus

22. Locating earthquakes

23. Measuring Earthquakes
The Richter Magnitude Scale
A scale of earthquake intensity based on the recorded heights, or amplitudes, of the seismic waves recorded on a seismograph
A logarithmic scale—a 10 fold increase in amplitude for each unit
Moment Magnitude Scale
A measure of earthquake strength that is based on the rupture size, rock properties, and amount of displacement on the fault surface

24. Measuring Earthquakes
Richter magnitude 6
Richter magnitude 7
Richter magnitude 8

25. Studying Earth’s Interior
Seismic discontinuity
A boundary inside Earth where the velocities of seismic waves change abruptly

26. Studying Earth’s Interior

27. Studying Earth’s Interior
Three things can happen to seismic waves when they meet a boundary
Refraction: bent as they pass from one material to another
Reflection: some or all of the wave energy bounces back
Absorption: some or all of the wave energy is blocked

28. How geologists look into Earth’s interior
Seismic tomography
Allows geologists to image inside of Earth
Direct observation
Drilling
Xenoliths
Indirect observation
Magnetism
Density

29. Diamonds!

30. A Multilayered Planet Crust
The outermost compositional layer of the solid Earth, part of the Lithosphere
Thickness ranges between 8 kilometers (oceanic) and 45 km (continental)

31. A Multilayered Planet

32. A Multilayered Planet Mantle
The middle compositional layer of Earth, between the core and the crust
Comprised primarily of olivine and pyroxene
Asthenosphere: mantle where rock is near melting
Mantle-core boundary: mesosphere

33. A Multilayered Planet

34. A Multilayered Planet Core
Innermost layer, where the magnetic field is generated and much geothermal energy resides
Separated into outer core (liquid) and inner core (solid)

35. Critical Thinking
If you were on a ship in the ocean, would you be able to feel an earthquake that occurred below you, on the ocean floor?
Do you think there is no limit to the magnitude of earthquakes?
What kind of wave would you expect to travel faster: a seismic wave or a tsunami wave?