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