EarthquakesEarthquakesChapter 8
What is an earthquake?• Vibration of Earth
produced by a sudden release of energy• Movements along the
fault line.
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
Elastic ReboundHypothesis
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
Foreshock vs. Aftershock
Foreshock – small quake that comes before a major earthquake
Aftershock – small quake that comes after a major earthquake
Seismology Seismology – study
of earthquake waves
Seismograph – instruments that record earthquake waves
Seismograms – the record made by a seismograph
Earthquake wavesSurface
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
Earthquake waves •P 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
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
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
The ScalesRichter 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
The ScalesMoment 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
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
Tsunami Seismic sea waves Triggered by an
earthquake occurring where a slab of the ocean floor is displaced vertically along a fault
Other DangersLandslides
Sinking of the ground triggered by the vibration
Greatest damage to structures
Fires Caused by ruptured
gas lines
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
Layers of the EarthLayers defined by
compositionCrust
Thin, rocky outer layer of Earth
Either oceanic crust or continental crust
Oceanic crust is 7 km thick
Mantle 82% of the Earth’s
volumeSolid rock at the top,
liquid at the bottom
CoreComposed of iron-nickel
alloyExtreme pressure found
in the center of the core
Layers defined by
Physical PropertiesLithosphere
The crust and uppermost mantle
Cool, rigid shell 100 km thick
Asthenosphere Soft, comparatively weak layer Below the lithosphere Rock close to melting
Outer CoreLiquid layer 2260 km thickMetallic iron generates
Earth’s magnetic fieldInner Core
Solid layer having a radius of 1220 km
High temperatures and high pressure
Nickel mostly
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