Earthquakes

Section 1:Forces within Earth SWBAT define stress and strain as they apply to

rocks.SWBAT distinguish among the three types of faults.SWBAT contrast the three types of seismic waves.

Earthquakes: Natural vibrations of the ground

caused by movement along gigantic fractures in Earth’s crust, or sometimes by volcanic eruptions.

Forces Within the Earth

Forces within Earth

Focus: the point where an earthquake originates.

Epicenter: the point on the Earth’s surface directly above the focus.

Movement along faults causes most earthquakes.

When rocks fracture or break deep within

Earth’s crust, earthquakes occur. Stress: the forces per unit area acting on a

material Fractures form when stress exceeds the

strength of the rock. Three types of stress acts on Earth’s rocks:

Compression Tension Shear

Forces Within Earth

Compression: is stress that decreases the volume of a material.

Tension: stress that pulls a material apart.

Shear: Stress that causes a material to twist.

Three Types of Stress

Stress-Strain Curve

Strain: The deformation of materials in response to stress.

Stress-Strain Curve: A graph that shows when stress applied to rocks is plotted against strain. Two Segments:

Straight Segment – produced by low stresses (elastic strain) Curved Segment – produced by high

stresses (ductile deformation)

Stress-Strain Curve

Elastic Strain: causes a material to

bend and stretch; material can return to its original size and shape.

Ductile Deformation: when stress exceeds a certain value; this type of strain causes permanent deformation.

Stress-Strain Curve

Three Types of Faults

Three types of faults

Three Types of Faults

Many kinds of rock fail when stress is applied too quickly.

The resulting fracture or system of fractures, along which movement occurs is a fault.

Three Types of Faults

Reverse Faults: fractures that form as a result of horizontal compression. Compressional force results in horizontal shortening of the crust.

Three Types of Faults

Normal Fault: fractures caused by horizontal tension. The movement is partially horizontal and partially vertical. This results in extension of the crust.

Three Types of Faults

Strike-Slip Fault: fractures caused by horizontal shear. Movement is mainly horizontal; motion along this fault has offset features that were originally continuous along the fault.

Seismic Waves: vibrations of the

ground during an earthquake. Every earthquake generates 3 types of

seismic waves: Primary waves (P-waves) Secondary waves (S-waves) Surface Waves (Love and Rayleigh waves)

Seismic Waves

P-waves (primary): “push-pull” waves that travel

through solids and liquids. P-waves squeeze and pull rocks in the same direction as the wave travels. P-waves travel faster than S-waves or surface waves.

Seismic Waves

S-waves (secondary): “shake” waves travel slower

than P-waves and travel only through solids; causes rock particles to move at right angles in relation to the direction of the waves.

Seismic Waves

Surface waves: (Love and Rayleigh waves)

move in two directions as they pass through rock. An up-and-down movement like and ocean wave occurs, as well as a side-to-side movement.

Seismic Waves

Seismic Waves

Love and Rayleigh Waves are the two types of surface waves.

Seismic Waves

Earthquakes

Section 2: Seismic Waves and Earth’s Interior

SWBAT describe how a seismograph works.

SWBAT explain how seismic waves have been used to determine the structure and

composition of Earth’s interior.

Seismometer (also called a seismograph):

instrument used to detect and record seismic waves. A frame is anchored to the ground with a mass and pen suspended from a spring or wire. When the ground shakes, the frames shakes causing the pen to record the seismic waves on paper surrounding a rotating drum.

Seismogram: record produced by a seismometer.

Seismic Waves and Earth’s Interior

Seismic Waves & Earth’s Interior

For ANY distance

from the epicenter, P-waves always arrive first at a seismic facility.

With increasing travel distance, the time separation between P-waves and S-waves increases.

Seismic Waves & Earth’s Interior

Travel-Time Curves

Most of what is known about Earth’s interior

comes from the study of seismic waves. Seismic waves change speed and

direction when they encounter different materials.

P-waves and S-waves follow fairly direct paths when traveling through the mantle.

When P-waves strike the core, they refract or bend, creating a P-wave shadow zone between 11,000km and 16,000 km from the epicenter.

Seismic Waves & Earth’s Interior

Seismic Waves & Earth’s Interior

Earthquakes

Section 3: Measuring & Locating Earthquakes SWBAT Compare and Contrast earthquake magnitude and

intensity and the scales used to measure each. SWBAT explain why data from at least three seismic

stations are needed to locate an earthquake’s epicenter. SWBAT describe Earth’s seismic belts.

Magnitude: the amount of energy

released during an earthquake. Measured using the Richter Scale and Moment Magnitude Scale.

Richter Scale: based on the size of the largest seismic waves generated by the earthquake.

Moment Magnitude Scale: (most seismologists today use this scale) values are estimated from the size of several types of seismic waves. Size of fault rupture, amount of movement along the fault, and the rock’s stiffness are also taken into account.

Earthquake Magnitude & Intensity

Magnitude Scales

Magnitude ScalesMoment Magnitude Scale

Intensity: the measure of

the amount of damage done to the structures involved. Intensity depends primarily on the amplitude of the surface waves generated.

Intensity decreases as the distance from the epicenter increases.

Intensity values from the Modified Mercalli Scale can be compiled to make a seismic-intensity map.

Measuring Intensity

Modified Mercalli

Scale: used to measure intensity; scale uses roman numerals from I to XII. Specific effects or damage corresponds to specific numerals; the higher the numeral, the worse the damage.

Measuring Intensity

Both magnitude and intensity reflect the

size of seismic waves generated by the earthquake.

Intensity is also determined by the depth of the earthquake’s focus.

Shallow-focus earthquakes often cause more damage than deep-focus earthquakes.

Deep-focus earthquakes produces smaller vibrations at the epicenter than a shallow-focus earthquake.

Magnitude Vs. Intensity

The distance to an

earthquake’s epicenter (epicentral distance) can be determined by plotting three seismic stations on a map. A circle whose radius is equal to the corresponding epicentral distance is plotted around each station. The point of intersection of these circles is the earthquake’s epicenter.

Distance to an Earthquake

The epicentral distance can also be calculated

using the P-S separation on a seismogram and the distance on a travel-time graph at which the P-curve and S-curve have the same separation.

Distance to an Earthquake

Distance to an Earthquake

Locating Epicenters

Distance to an Earthquake

Recording Seismic Waves

The majority of the world’s earthquakes

occur in relatively narrow seismic belts that separate large regions with little or no seismic activity.

Seismic Belts

Earthquakes

Section 4: Earthquakes and SocietySWBAT discuss factors that affect the amount of damage done by an earthquake. SWBAT explain some of the factors considered in earthquake possibility studies. SWBAT discuss some of the hazards associated with earthquakes. SWBAT define seismic gaps.

The damage produced by an earthquake

is directly related to the strength or quality of the structures involved.

Severe Damage Occurs to Unreinforced Buildings: Concrete Stone Brick

More resistant to structural failure: Wood high-rise steel-frame buildings

Earthquake Hazards

Pancaking: when the supporting walls of

the ground floor fail causing the upper floors to fall and collapse as they hit the lower floors or ground floor.

Another type of structural failure is related to the height of the building. When shaking caused by the quake has the same vibrations of the natural sway of the building, it collapses.

Structural Failure

Structural FailurePancaking

Areas with fluid-saturated sand, seismic

vibrations cause subsurface materials to liquefy and behave like quicksand. This can generate landslides even in areas with low relief.

Soil liquefaction can cause trees and houses to fall over or they may sink into the ground. Underground pipes and tanks may rise to the surface.

Land and Soil Failure

Soil Liquefaction

Fault Scarps: areas of great vertical

offset produced by fault movements associated with earthquakes.

Fault Scarps

Tsunami: an ocean

wave generated by vertical motions of the seafloor during an earthquake.

Tsunami

Seismic Risk Maps

Earthquake prediction is based on probability

studies. Probability Studies are based on two factors:

The history of earthquakes in an area The rate at which strain builds up in the rocks

Probability studies also take into considerations seismic gaps.

Seismic Gaps are sections of active faults that haven’t experienced significant earthquakes for a long period of time.

Earthquake Prediction

Add notes to each major earthquake as I tell

you more about it or of I show a video clip

Earthquake Case Studies

Earthquakes and Society

Nepal Earthquake: April 2015

https://www.youtube.com/watch?v=949TICL4MMc

Japan March 2011

Japan March 2011

Japan March 2011

https://www.youtube.com/watch?v=K6cJo_gD8TU

Earthquakes and Society

Indonesia Earthquake 2004

Earthquakes and Society

Sir Lanka Tsunami after Indonesia Earthquake 2004

Earthquakes and Society

:

Sir Lanka Tsunami after Earthquake

Earthquakes and Society

Sir Lanka Tsunami after Earthquake: https://www.youtube.com/watch?v=b9DMiy_DVok (part 1) https://www.youtube.com/watch?v=UMQEgJR0FcA (part 2) https://www.youtube.com/watch?v=uAB4zvMlhNo (part 3) https://www.youtube.com/watch?v=Z3pp-kFNnbs (part 4) https://www.youtube.com/watch?v=viWgtap2_IM (part 5) https://www.youtube.com/watch?v=Db5hB2mugvg (part 6) https://www.youtube.com/watch?v=KBsQAIyVWn0 (part 7) https://www.youtube.com/watch?v=fu2aWPXpiWo (part 8)

Earthquakes and Society

Haiti Earthquake: January 2010 Pictures is of Port au Prince

Earthquakes and Society

1994 Northridge, Ca

Earthquakes and Society

1989 San Francisco Earthquake

Earthquakes and Society

San Francisco Earthquake: 1906 Pictured below is City Hall

Earthquakes and Society

San Francisco Earthquake: 1906

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