1. Earthquakes

2. What is an earthquake?
Vibration of Earth produced by a sudden release of energy
Movements along the fault line.

3. Focus, Epicenter and Faults
Focus – point within the Earth where the Earthquake starts
Epicenter – location on the surface of Earth directly above the focus
Fault- associated with earthquake activity where movement has occurred

4. Elastic Rebound Hypothesis
Release of built-up energy
Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces
When the strength of the rock is exceeded, it suddenly breaks, causing vibration of an earthquake

5. Foreshock vs. Aftershock
Foreshock – small quake that comes before a major earthquake
Aftershock – small quake that comes after a major earthquake

6. Seismology Seismology – study of earthquake waves
Seismograph – instruments that record earthquake waves
Seismograms – the record made by a seismograph

7. Earthquake waves Surface
Seismic waves that travel along Earth’s outer layer
Move up, down, and side to side
Most destructive earthquake waves
Last to arrive at the seismograph

8. Earthquake waves P waves S waves
They push (compress) and pull (expand) rocks in the direction the wave travels
Also known as compression waves
Can travel through solid, liquid, and gas
Fastest waves
S waves
Shakes particles at right angles to their direction of travel
Also known as transverse waves
Can only travel through solids
Slower than P waves but faster than surface waves

9. Locating an earthquake
The difference in velocities of a P wave and S wave provides a way to locate the epicenter
Use a travel-time graph
Need at least three seismograph station data

10. Intensity and Magnitude of Earthquakes
Two different types of measurements to describe the size of an earthquake (intensity and magnitude)
Intensity
A measure of the amount of earthquake shaking at a given location based on the amount of damage
Magnitude
A measure of the size of seismic waves or the amount of energy released at the source of an earthquake

11. The Scales Richter Scale Measures the magnitude of an earthquake
Based on the amplitude of the largest seismic wave
10-fold system (ex: The amount of shaking for a 5/0 earthquake is 10 times greater than the shaking produced by an earthquake of 4.0 on the Richter Scale

12. The Scales Moment Magnitude
More precise means of measuring earthquakes
Amount of displacement that occurs along a fault zone
Calculated using several factors
Average amount of movement along the fault
Area of the surface break
Strength of the broken rock
Most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakes

13. Destruction from Earthquakes
Seismic Vibration- Damage to building depend on several factors
Intensity and duration of vibration
Nature of the material on which the structure is built
Design of the structure
Liquefaction
Stable soil turns into a liquid that is not able to support buildings or other structure

14. Tsunami Seismic sea waves
Triggered by an earthquake occurring where a slab of the ocean floor is displaced vertically along a fault
tsunami videos

15. Other Dangers Landslides Fires
Sinking of the ground triggered by the vibration
Greatest damage to structures
Fires
Caused by ruptured gas lines

16. Predicting Earthquakes
Short range
Methods for short range predictions of earthquakes have not been successful
Long range
Based on the idea that earthquakes are repetitive
Seismic gap: an area along a fault where there has not been any earthquake for a long- period of time

17. Part of the Earth Layers defined by composition Crust
Thin, rocky other layer of Earth
Either oceanic crust or continental crust
Oceanic crust is 7 km thick

18. Mantle Core 82% of the Earth’s volume
Solid rock at the top, liquid at the bottom
Core
Composed of iron-nickel alloy
Extreme pressure found in the center of the core

19. Layers defined by Physical Properties
Lithosphere
The crust and uppermost mantle
Cool, rigid shell
100 km thick
Asthenosphere
Soft, comparatively weak layer
Below the lithosphere
Rock close to melting

20. Outer Core Inner Core Liquid layer 2260 km thick
Metallic iron generates Earth’s magnetic field
Inner Core
Solid layer having a radius of 1220 km
High temperatures and high pressure
Nickel mostly