earthquakes and earth’s interiorhomepages.wmich.edu/~kehew/geos1000/ch05_earthquakes.pdf•explain...

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EARTHQUAKES AND

EARTH’S INTERIOR

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.

Megathrust earthquakes

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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

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

Earthquakes and plate motion

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Earthquake Hazards and

Predictions

• Primary hazards

– Collapsing buildings, bridges and other structures

– Aftershock

• Secondary hazards

– Landslides, fires, ground liquefaction, tsunamis

Earthquake hazards

Landslide, Huascaran, Peru Open fissure, Golcuk, Turkey

Earthquake hazards

Fire, San Francisco, California Ground liquification, Niigata, Japan

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Tsunami (Seismic Sea Wave)

The Sumatra-Andaman Tsunami

(2004)

Earthquake prediction

• Short-term prediction and early warning

– Precursor phenomena

– Foreshocks

• Long-term forecasting

• Paleoseismology

– The study of prehistoric earthquakes

– Seismic gaps

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When did the last

earthquake

occur?

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

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

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The Science of Seismology

Seismic waves• Body wave

– Travels through Earth’s

interior

• Surface wave

– Travels along Earth’s surface

• Focus

– Where rupture commences

and an earthquake’s energy is

first released

• Epicenter-

– surface point above focus

Locating earthquakes• Compressional 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

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Locating earthquakes

Locating earthquakes

Locating earthquakes

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Locating earthquakes

• Epicenter

– The point on Earth’s

surface directly above an

earthquake’s focus

Three measuring

stations are

necessary to locate

an epicenter

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

Measuring Earthquakes

Richter magnitude 6Richter magnitude 6 Richter magnitude 7Richter magnitude 7

Richter magnitude 8Richter magnitude 8

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Studying Earth’s Interior

• Seismic discontinuity

– A boundary inside Earth

where the velocities of

seismic waves change

abruptly

S waves cannot pass

through the outer core

because it is liquid.

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)

• 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

• Core

– Iron-nickel alloy

– Outer core is molten, inner core is solid

A Multilayered PlanetCompositional layers

Different rock

properties

and behavior

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• Core

– Innermost layer,

where the

magnetic field is

generated and

much geothermal

energy resides

– Separated into

outer core (liquid)

and inner core

(solid)

A Multilayered Planet